Linus Pauling Interview, December 27, 1990

THOMAS HAGER: Interview with Linus Pauling. December 27th, 1990.

LINUS PAULING: Hello?

TH: Hi, Linus?

LP: Yes.

TH: Linus, this is Tom Hager.

LP: Well, hello, Tom.

TH: Well, hello. Merry Christmas.

LP: Thanks for that book that you sent me.

TH: Oh, you got it. Good.

LP: Yes, I've enjoyed reading it.

TH: Well, I hoped it would get there in time. I remember when I was down there before I had asked you if you had that, and I remembered you saying you hadn't, so I hope it's not a duplicate.

LP: Yes.

TH: Good.

LP: I've checked up on almost all the places in Oregon where I've spent time, some time.

TH: Well, I find that it's sort of a useful thing to have when you're driving around, or just for fun, just to look up the names of places. And of course, with your grandfather being in there...

LP: Yes.

TH: ...too, that makes it kind of interesting also, as well. Now listen, when we 00:01:00spoke last, we had talked about setting aside some time today for a talk. Does that still look good to you?

LP: Yes, that's all right.

TH: Okay. I wanted to pick up from where we left off. The last time that I spoke to you, we'd sort of covered things up until you were getting ready to go to Caltech from Oregon Agricultural College, and I kind of wanted to pick things up from about that time, if that's okay with you.

LP: Yes.

TH: But when I was going over things, Linus, I was interested in trying to trace back the- you know, through your education, before you went to Caltech and started doing crystallography work with Dickinson, I wanted to sort of pinpoint when your thinking started to turn from chemical engineering and sort of a straightforward approach to chemistry at that time to the idea of structure. 00:02:00That move away from engineering and toward the kind of structural work that you started doing with Dickinson. I know that you were interested in metallography, and you did some of that at Oregon Agricultural College, and of course, that involves some sort of structural thinking, but still, it seemed like quite a leap from that into sort of the theme of structural thinking that you carried throughout your career.

LP: Well, I remember that in the course in metallography, we had a textbook - I don't remember, and I don't think I have the textbook anymore - in which there was a discussion with a theory of malleability and ductility of metals. Metals differ from many other substances, salts, and organic compounds, in that these 00:03:00other substances tend to be brittle. If you hit them with a hammer, hit a crystal of salt or sugar, or most crystals, they fracture into a lot of small pieces. But a metal and alloy, most alloys, when they are hit with a hammer, just flatten out which means they are malleable. Or if you take iron and pull it through a smaller hole, a dye, it stretches to a longer wire, they're ductile. The theory that they gave was the theory that a slip occurs along planes of atoms. Essentially, you have a hole where there isn't any atom, and that an atom 00:04:00next to that hole moves into it, and then the next one moves into it, and so on, in the direction determined by the stress to which the metal is exposed. So, that was a discussion of a property of metals that was based on structure, the property being malleability and ductility based upon structure. Well, I'm not sure, I think I had that course in my junior year, the start of my junior year.

TH: And prior to that, had you- I know that it was in that break in-between sophomore and junior year that you were looking, and you first were exposed to-

LP: Yes. Well, I've told you- I think I may have told you that my office was in the chemistry library, along with Prof. Fulton's stenographer. She had a desk with a typewriter, and I had a desk there. Well, my teaching load was so heavy that I wasn't in the office very much, but the hours when I wasn't teaching, I often read the journals, the chemical journals that came. So, I read, in 1919, the 1919 papers by Irving Langmuir on the electronic theory of valence and went back, got out the 1917 issue containing G.N. Lewis's paper, which Langmuir 00:06:00referred to. He was careful to give credit to Lewis. And I became very interested in the electronic theory of metals, of valence, G.N. Lewis's shared electron bond ends, also Langmuir's expansion, application with the theory, and additions to it. And I gave a seminar, chemistry seminar, at which I talked about the electronic theory of valence. So, that was during that year, 1919, 1920. There were only two seminars, as I recall, two chemistry seminars 00:07:00[laughs]. I gave one of them.

TH: Now, did you-when you started thinking then about this problem of the ductility of metals, did you do more than think about it? Did you actually do some experiments along those lines to-?

LP: No. But the next year, or during my senior year, I decided to do some chemical research. It may have been just the last term. And I may have got credit for it. I'm not sure. I did it under Graf's supervision. I had the idea that if you crystalized iron, grew crystals of iron in a magnetic field, the crystals would be oriented. And to grow the crystals of iron, I was going to use 00:08:00electrolysis. Well, and metallographic methods of polishing a sample and then etching it and looking at the etch figures to see how the little crystallites are oriented. Well, of course, I was doing a lot of other things the same time and I carried out the experiment of depositing iron electrolytically on a piece of a bar of copper. But when I tried to polish the deposits, it just came off. The iron, my deposit of iron, was not coherent enough for me to be able to 00:09:00polish it. So, nothing came of that effort on my part to carry out a sort of crystallography experiment.

TH: This, and of course involving magnetism. Now, your interest in magnetism went back a ways too. Didn't you- you tried, I think when you were doing some of that summer work on the road crews, weren't you looking at the magnetic properties of elements in the periodic table and thinking about-

LP: Yes. Well, that started the summer before this year. That had been my sophomore year while I was down at Grave Creek. I kept an eye on the paving plants and the materials that they were using, and the mix of materials and the temperature, and so on. But I had time enough so that I could do some reading 00:10:00too, and I remember that I had a copy, early edition of the Handbook of Chemistry and Physics, which had tables of properties of substances. So, I would amuse myself, spend time just looking at the numbers in these tables. Or the words, such as red or black, or the color, you know. Or soluble. Solubility in water, and other solvents.

And one of the tables that interested me, or two or three of the tables that interested me, were about magnetic properties. So, I tried to understand why some substances are ferromagnetic and some aren't ferromagnetic, and some are 00:11:00diamagnetic. But I didn't have a background of knowledge of theory, so that this effort - pertinent theory - so, this effort was completely unsuccessful. It wasn't until I got to Caltech and took their courses, mainly with Tolman, that I began to understand what the magnetic properties were and what their structural origin was.

TH: It sounds like you have a little cold today.

LP: I don't have a cold, but [laughs], well, I don't have a cold in the sense of being troubled by it, because I've been taking my vitamin C as usual. But the 00:12:00cold weather here has caused me to have some nasal secretions, especially in the morning when I get up and it's cold.

TH: Yeah. Now listen, to get back to the question of metals and working with metals, I've looked at some of your notebooks from Oregon Agricultural College, and you had kept some of the papers from the metallography class in it, and some of the things that you had written there. It certainly looked like you were enthusiastic. I mean, without knowing anything else about it, about that field. Now, had you considered sticking with metals at one point and sort of heading in that direction?

LP: Well, when I was nominated by OAC for the...

TH: For the Rhodes.

LP: ...the Rhodes Scholarship, it was a requirement that the person write to 00:13:00someone associated with the college at Oxford and get permission to come. And I found that there was a man - and I don't remember his name - doing metallography at Oxford. So, I wrote to him. Well, I may have got an answer from him too, but I just asked, [sighs], Jeff [sic] Mead, Cliff Mead, to check through, and he sent me all of the Rhode Scholarship stuff, and these letters aren't in it. I've looked for the letters before.

TH: To see what you had asked him about?

LP: Well, I wrote to him saying I was interested in metals and alloys and if I 00:14:00got a Rhodes Scholarship, could I come and work with him? Well, later on when I was at Oxford, or even earlier before I went there, I learned about a man at Oxford, who's dead now, who was working in this field. That was Hume-Rothery. And, well, I didn't ever ask him who this fellow might have been that I'd written to earlier. I don't think he was on the staff.

TH: So, there was, had you gotten the Rhodes, you might have ended up going in that direction more.

LP: Maybe. Well, I probably wouldn't have accepted it because I don't think the money was enough. I think a Rhodes Scholar had to have some extra money to get along on what he would get from the Rhodes Trust.

TH: Was that perceived, at the time - of course, now the Rhodes Scholarships 00:15:00have a certain panache. I mean, they're considered prestigious. Was it, at that point in time, was that also considered quite an honor, to be nominated for a Rhodes?

LP: Oh, yes.

TH: Yeah. Were you- what were your feelings when you learned you didn't get it?

LP: What is it?

TH: What were your feelings when you learned that you didn't get the Rhodes Scholarship?

LP: Well, I was relieved because, [laughs], that I wouldn't have to decide whether to accept it or not. [Both laugh].

TH: And of course, Paul Emmett was nominated too, wasn't he? At the same-

LP: Yes. He and I, two chemical engineers [laughs], were the ones that were nominated by OAC.

TH: Yeah. When you decided to go to graduate school, tell me first, why didn't you just stop with your undergraduate degree and go into chemical engineering? 00:16:00What was your motivation at that point for even considering graduate school at all?

LP: Well, there was much talk about going to graduate school then. There were only a few members of the faculty who had Ph.D. degrees, but there were some. And about that time, or a little later, there was a sort of faculty club, a club of faculty members called The Order of the Spoon. When I went back in 1933 to get my honorary doctorate, I was initiated into The Order of the Spoon, which consisted just in giving me a big wooden spoon about three feet long, or 30 inches long. And The Order of the Spoon had been set up by a few of the faculty members who had doctor's degrees. To be eligible for it, you have to have your 00:17:00doctor's degree. Well, that was, of course, 11 years later than when I went to Caltech. But about 1920, there came a new professor of chemical engineering. Haven't I told you about him?

TH: Yeah, Floyd Rowland.

LP: Floyd Rowland.

TH: Yes. And no, you had mentioned that he was very, very-that he promoted graduate school.

LP: That's right. So, I think when I graduated there were about 12 chemical engineers who got their bachelor's degrees, and something like seven of them went off for graduate work. And he was largely responsible. In my case, I remember during this year when I was full-time teaching, before Floyd Rowland 00:18:00came, I believe, Johnny Fulton, the head of the Chemistry Department, showed me a flyer that he had received from Caltech.

TH: Oh, that's right. You had written them even in- this was in-between your sophomore and junior years. You had written Caltech asking to come down as an undergraduate. Is that correct?

LP: That's right, yes. And Stuart Bates answered the letter. A. A. Noyes was away, I think at the time. Stuart Bates answered me, and he said that I had said that I would have to earn my living, and it just wasn't possible for an undergraduate at Caltech.

TH: Yeah. Now, you had- that break in-between your sophomore and junior years was basically for the purpose of earning money. Is that right?

LP: Yes, that's right.

TH: And you-

LP: Well, I had to take a cut in salary. I was getting $125 a month as a paving 00:19:00plant inspector. OAC offered me - and I accepted - $100 a month.

TH: You had mentioned in a previous interview that I came across, you had said, about that period of time at the end of your sophomore year, you'd been sending money back to your mother, and that she had- I was unclear about what happened at the end of your sophomore year. It seemed the implication from the interview was that you'd been sending money back to your mother and that she had had to use it. Was she supposed to be saving money for you, for college?

LP: Well, presumably she was, yes. That's what she had done the previous summer. You see, I had made money living at home and then given my salary to her, and 00:20:00then she sent me $25 a month, I think, each of the two previous years. So, I had made money during the summer and given it to her, and then she had sent it back to me. Some of it, anyway. Or perhaps even more than I had made. I'm not sure.

But I was making $125 a month as paving plant inspector and spending almost nothing, in that... of need. This was an isolated place at Grave Creek. There was no place to eat and no place to live [laughs]. So, the contractor allowed me to live in a tent, along with the workmen. A good size tent with perhaps a dozen 00:21:00men, with cots in it. And I'd wash in the creek, Grave Creek, in the morning. And I got my meals at the cookhouse for the crew. There was a cook who provided breakfast, lunch, and dinner every day. And it didn't cost me anything. But then, when September came, I was planning to leave the job and go to Oregon State, and my mother wrote saying that she just couldn't send me money. So, another month or six weeks went by and I got a telegram offering me the job at Corvallis.

TH: I see. And what was her reason for not being able to send you money? Was it simply-?

LP: That she didn't have any money.

TH: I see. And including the money that you had sent her?

LP: Yes, yes.

TH: I see, I see.

LP: Well, I'm sure she had a very hard time. When I went to Pasadena in 1922, I had borrowed some money at OAC from Johnny Fulton, and I borrowed $1,000 and gave it to my mother at that time.

TH: You borrowed the $1,000 from who? From Fulton?

LP: No, I borrowed that from my Uncle Jim.

TH: Oh, from Judge Campbell.

LP: Yes. And I paid him back during the next year or two and paid Johnny Fulton back too. It may have- may be that it took three years to pay off this debt.

TH: And that was at the time you left OAC and went down to Caltech, that you borrowed that money?

LP: Yes.

TH: Okay. Now, when you were deciding where to go to graduate school, you applied to six different places or so, I understand?

LP: Yes.

TH: Including Harvard and Berkeley and Caltech. Do you remember what the other places were?

LP: Well, Illinois. I remember Rowland, Floyd Rowland had got his Ph.D. at Illinois. It was the leading American university in organic chemistry at that time. Well, I wasn't especially interested in organic chemistry. Not at all interested, in fact, but I applied there. And I may have applied- that makes four places. Possibly I applied somewhere else. I don't remember.

TH: Did you- you know, now, often when people go to graduate school, they have a pretty- many students will have at least a general direction in mind for their studies. I mean, they'll apply to places that fall in line with what they perceive to be their career path. Now, I know that Illinois was heavily oriented and best known for its organic chemistry, where Berkeley was of course where Lewis was. And you knew of Lewis, and you had mentioned to me that you'd been very impressed by him just through his writings. But they're two very different programs. Did you have an idea about the direction that you wanted to go in in mind, or were you just applying to the most pres- these are certainly the most prestigious programs.

LP: Well, I think physical chemistry is what interested me. Perhaps inorganic chemistry. Of course, Illinois was not too bad in inorganic chemistry and 00:25:00physical chemistry, too, but they were outstanding in organic chemistry.

TH: Certainly, in lines of physical chemistry, the Lewis program would have been, I suppose, the premier program in the nation for physical chemistry at that time. Was that your reading of it too, or did you- I'm always interested in the question of, if Berkeley had come through and responded to your request and you had to make a choice between Caltech and Berkeley, where you would have gone.

LP: Well, I'm not sure. I'm not sure which place I would have selected.

TH: Tell me about the reputation that Caltech had at that time. Of course, the institution had just been gathering, sort of building its reputation since the 00:26:00time that they brought Noyes and Millikan in full time. What sort of things were you hearing about Caltech that got you interested in that program?

LP: Well, Johnny Fulton came around to show me that flyer, and he said, "Perhaps this is a place you ought to go." I think they were offering $350 for the nine months of the school year as a stipend, with no charge for tuition at that time. And, so far as its reputation, I knew that Millikan had gone there. I'm pretty sure I knew then my high school textbook in physics was Millikan and Gale. And A. A. Noyes, I think I used A. A. Noyes's book of qualitative analysis.

TH: Well, and you had Noyes and Sherrill. You were working at-weren't working at problems that Noyes and Sherrill-

LP: Yes. That was in my senior- yes, that was during the year when I accepted the job, so I knew about Noyes and Sherrill. Well, I knew about Noyes, but I didn't have Noyes and Sherrill 'til after I'd accepted that.

TH: Oh, I see. Okay.

LP: Dr. Noyes sent me the proof sheets and sent Paul Emmett the proof sheets.

TH: Oh.

LP: And asked us to work the problems of the first nine chapters. There were 13 chapters. So, I have-well, they're up in Corvallis. There is a manuscript held together by paper clips.

TH: Oh, of that draft copy, yeah. Proof copy.

LP: No, no, I think that's- I don't think I have that, but of my solutions to 00:28:00the problems. Not only the first nine chapters but also the other four chapters. Noyes taught the course the fall term.

TH: Okay, so he sort of gave you that as a preparatory...

LP: Well, he wrote to say that the course in physical chemistry that we had had, Paul Emmett and I, was no doubt pretty poor because we used a textbook written by a member of the staff, actually, at MIT where Noyes was. But Noyes considered it was a pretty poor textbook, which it was. So, he suggested to Paul and me - we weren't together. You know, we were different places during the summer, but suggested that we work these problems.

TH: Had you had any personal contact with Noyes prior to that correspondence when you applied for graduate school?

LP: No. The first correspondence with Noyes, well I may have written to him two years earlier when Bates answered the letter. But when he wrote the letter offering the appointment the spring of '22, that was my first letter from him. And after I had accepted, he wrote saying he thought that I should do X-ray crystallography with Dickinson.

TH: Yeah, I was going to ask you about that too since that wasn't something that you had done before. I was interested in how Dickinson became your major professor there. So, apparently, Noyes was the one who suggested that.

LP: Yes. And probably the suggestion was made on the basis of what I had said in 00:30:00my letter of application. I'm sure it's in Corvallis. I don't have it.

TH: Yeah.

LP: So, I had probably expressed an interest in molecular structure and he carried that over to crystal structure.

TH: Uh-huh. But it certainly, in terms of- when you arrived at-[tape ends].

LP: Yes, he had just arrived I think the same summer.

TH: Yeah, because it seemed to me that, judging from the classes that Tolman was teaching, and of course, he seemed to be more aligned to the strictly sort of physics side of the equation and working a lot in terms of introducing the ideas of some of the early quantum theory and so forth. It seemed as though his interests and yours might have been more closely aligned than yours and Roscoe Dickinson's. But that may just be looking at it in retrospect, I guess. It just 00:31:00seemed interesting to me that you didn't end up with Tolman as a major professor instead of Dickinson.

LP: Well, of course, Noyes knew Tolman well, but he- well, I don't know that I can comment much on that.

TH: The- Roscoe Dickinson wasn't all that much older than you, was he? Was he fairly young?

LP: He was 10 years older. He was a National Research Council Fellow that, when I first came down, and then I think he was made assistant professor later. Two or three years later.

TH: Tell me how you and he got along. When you first came down and you first introduced yourself to Dickinson, did he strike you as being austere, off-putting, friendly, warm? Did you seem to hit it off, or was it a long time 00:32:00building a relationship?

LP: Oh, he was warm and friendly, and I was very pleased to be working with him.

TH: Did you have much contact with Noyes at the beginning? Personal contact, I mean. I'm trying to get a picture of what Caltech was like then. The faculty was still fairly small. The number of graduate students, I understand, was growing but was still fairly small when you first arrived.

LP: Yes. Well, Noyes invited me and two or three other graduate students, and perhaps a postdoctoral man, to go to the desert with him in his car and stay overnight. So- and he also, later, invited me and my wife, and later our 00:33:00children, or one of them, to come down to his home at Corona Del Mar. His summer home, or beach home. Well, he was- see, Dickinson was only 10 years older. Noyes, how much, 40 years older.

TH: Oh, yeah.

LP: Quite a difference. So, it's to be expected that my relations with Dickinson were different from those with Noyes. Dickinson and his wife took me to the desert too, for a couple of trips during that year.

TH: These are just like camping trips?

LP: Yes.

TH: And what-was it purely pleasure, or was chemistry discussed?

LP: Well, purely pleasure, I think [laughs].

TH: And was this- were these trips group trips? Were there a number of graduate students, or would they just takeout say one or...?

LP: Well, there were- Noyes took two or three with him on that trip to Coachella Valley. And I think there were about five people in the car. As I say, perhaps a graduate stude- a postdoctoral fellow and two or three graduate students. Three graduate students. Dickinson, the trips, there may have been three trips with Dickinson to the desert, Dickinson and his wife. And to either Coachella Valley down by Palm Springs or to Red Rock Canyon. Just me.

TH: So you actually, you had a very friendly relationship then, it sounds like.

LP: Yes. Yes, indeed.

TH: Were you his only graduate student at that time, or did he have others in the lab? When you first arrived, while he was still an NRC fellow, were you his only charge at that time?

LP: He may have had another graduate student or two. I don't remember about the first year, but by 1924, wasn't it? Or '25, he went to Europe on an international fellowship.

TH: Uh-huh.

LP: And I was in charge of the X-ray lab then. And in fact, from then on I was in charge of the X-ray lab.

TH: Oh, okay. And was this a shared-when you say the X-ray lab, was this a shared facility that people would come and use, the way that they share 00:36:00largescale equipment nowadays in a graduate school? Or was this strictly Dickinson's own equipment?

LP: All of the equipment there had been built by the department instrument maker under Dickinson's supervision. Or it was-I built one. I built a powder apparatus. And in general, about the only thing we bought was the X-ray tube. Coolidge X-ray tube.

TH: But when you were in charge of the lab, there were other- other people from other laboratories would come in other than Dickinson's own people. Or, was it strictly Dickinson's laboratory that used that equipment?

LP: Well, it was Dickinson's or my laboratory and we didn't have people coming in from other universities or other departments, even.

TH: Okay. Yeah, that's what I was wondering. I just-

LP: I had, over the course of years, about 1931, one man who got his Ph.D. in geology doing his research with me on the crystal structure of a metal, Appel de los Chapelle [?]. And some number of years later, another whose doctor's dissertation was with me, done under my supervision.

TH: And this was before you got your degree?

LP: Oh no, this is-

TH: Oh.

LP: I got my degree in 1925, so [Chapel], that was six years later.

TH: Oh, okay.

LP: But they were my graduate students, but their coursework was such that they 00:38:00got their degrees in geology.

TH: Going back to Noyes again, he was famous, or well-known, for working even in his leisure time, that he would be thinking about chemical problems and considering ideas that related to chemistry. Did you find, say on that trip that you took with him that one time into the desert, was his mind always on work, or did he seem to break away and have ideas about other things?

LP: Well, you've asked that question a few minutes ago [laughs]. I answered it, too.

TH: Okay. When did you first come in contact with Millikan, then? Was this- was there a lot of contact between the people in the chemistry end and Millikan as well?

LP: Well, we saw Millikan. This was a small institution. He would preside at the convocations. Weekly convocation of the whole institute; usually some speaker. And I signed up for a course with Millikan. I'm not sure that I ever finished it. I may have backed out after a while. That may have been my second year. A course on modern physics or something like that. Well, I just don't remember whether I got credit for it or whether I gave up on it as being too elementary.

TH: Right. What-he was gaining stature about that time. National stature as being-well, he was certainly one of the most well-known scientists in the nation 00:40:00just in terms of the public consciousness at that time. Was he almost a legendary figure among graduate students as well?

LP: Well, I don't know that he was a legendary figure, because he was there [both chuckle].

TH: What I mean to say is, his national stature was becoming so exalted, I guess.

LP: Yes. well, he got the Nobel Prize perhaps my first or second year. And his oil drop experiment was famous. All of the textbooks contained it.

TH: Was he a-well, I'll come back to Millikan a little later when you start working with him on more of an administrative level, but when you were a graduate student, who were your- were you friendly with other graduate students? Did you make any close friends among the other students while you were at Caltech?

LP: Oh, yes. Well, Bob Robertson, Howard Percy Robertson, who's... he's been dead a number of years, but he's referred to as one of the important early cosmologists. He and I and his wife and my wife were quite friendly. And we worked, to some extent, together on problems in the courses in mathematics that we took. Then there was another graduate student with whom I also worked on trying to solve problems in the courses of mathematics. His name was Ward, W-A-R-D. Morgan Ward. So, I was quite friendly with him, mainly through our 00:42:00common interests in mathematics. And among my own students, well, there was Hendricks. Sterling Hendricks. He had started graduate work with Roscoe Dickinson. When Roscoe went to Europe, then I inherited him, and he and I published two or three quite important early papers around 1925, 1926. But then, of course, there were many other students, fellow students, and students of mine later on. More postdoctoral people with whom I was friendly.

TH: Just a few names among those who stand out, people that you worked closely with or were close with. Any names stand out?

LP: Maury Huggins. Maurice Huggins. M. L. Huggins who came as a postdoctoral fellow, a National Research Council Fellow, I think, and was in our laboratory doing some X-ray crystallography. He had got his Ph.D. at Berkeley not as an X-ray crystallographer, but as a chemical bonds man of some sort. I'm not sure what his thesis was. So, I wrote a couple of papers with him later on. Kept in contact with him. Well, there were many other, many others who came and stayed 00:44:00awhile, mainly postdoctoral people. And then my own students, too.

TH: Tell me about your sort of work schedule. As you got into the graduate program and you began doing more laboratory work, what sort of a day would you put in? Would this be something where you'd go in quite early in the morning and stay quite late at night, or did you have more regular work hours? I'm trying to think of what your home schedule might have been at that time.

LP: Well, that first year, I lived with Paul Emmett and his mother. And Paul and I would go to the lab early in the morning. I had I think 45 hours, which in 00:45:00some universities would be called 15 hours of classwork. The advanced courses I was taking, mostly in physics and mathematics. And in addition, I spent a lot of time on research. Later on, the department made a rule that a teaching fellow could sign up for only 30 hours. But after dinner, I would go back to the lab and work until perhaps 11 o'clock at night.

TH: Okay, and that was-was that five days a week or seven days a week [laughs]?

LP: Well, on Saturday and Sunday I'd just work all day.

TH: Okay.

LP: And the second year, after we were married, sometimes I worked at home. Sometimes my wife and I went down to the lab after dinner and worked together on 00:46:00analysis and the X-ray photographs.

TH: But generally speaking, pretty much every night you'd be down working in the lab.

LP: Yes.

TH: Did Ava Helen ever give you any grief about that? Was she ever concerned about the fact that you were devoting so many hours to the laboratory? I mean at this-while you were at graduate school?

LP: Well, I think until Linus was born, March of the third year, my third year as graduate student, many times she went down to the lab in the evening with me. Other times, I stayed at home with her [laughs]. Once in a while, we would go to a movie or something like that, but not very often.

TH: Speaking of mathematics, now you didn't have the opportunity to take a lot 00:47:00of mathematics at OAC, and when you came into Caltech, had you had calculus?

LP: Oh, yes. Well, in high school I had four years of mathematics in my three and a half years there because my last term, I took two mathematics courses.

TH: Right, right.

LP: So, in college, my first year I had sophomore mathematics, which was calculus. And the first term of my second year, I had a course in analytic geometry, and that exhausted the mathematics in Corvallis. So, I took many courses in mathematics in Caltech.

TH: And what were-when you first came to Caltech, what did you start with in 00:48:00terms of mathematics? Do you remember?

LP: I think I started with advanced calculus, which is a sort of second-year calculus course, and vector analysis, course in vector analysis. Then I went on to integral equations. The calculus was- advanced calculus was largely differential and integral calculus on a more advanced level, but integral equations is a special branch of mathematics. And some courses in mathematical physics, as well as Newtonian potential theory, which is the same as 00:49:00electrostatic theory.

TH: A class that you liked very much, I remember.

LP: Yes. I may have had a course in theory of numbers with E. T. Bell, but I'm not sure about that.

TH: Okay. Basically, if I'm reading this correctly, all of the exposure that you had to quantum theory at Caltech would have been through Tolman, is that correct? Was he pretty much the one person who dealt with that?

LP: Well, I'm sure I may even have had a course in the Physics Department dealing with quantum theory. I don't remember, but most of my exposure to old quantum theory was with Tolman.

TH: And how was he as a teacher?

LP: Oh, he was great. He was fine. He- I was just reading about him recently, a 00:50:00statement that he was careful in preparing his lectures and would come in ahead of time and write out a lot of stuff on the blackboard. I wrote out an awful lot of stuff on the blackboard too, but I did it during the class hours, not ahead of time.

TH: [Chuckles] uh-huh. So he made, by being a good teacher then, I- quantum theory is a sort of a difficult concept, obviously. At the time, it was somewhat revolutionary. Your background had been, pretty much exclusively, was sort of classical physics up until then, correct?

LP: Yes.

TH: Yeah. And did he manage then to make the old quantum theory perfectly clear to you? At least clear as far as possible?

LP: Well, yes. And I think we had good textbooks, too. I think the first year, 00:51:00Tolman gave a course using Foote and Mohler, which had just come out, which was had the title The Origin of Spectra. It was about atomic structure, quantum theory, Bohr theory, and so on. And then we-Tolman gave a course using Sommerfeld up to about spectral medium. And I think one year we used the German edition of the book, and then the next year an English translation was published, and we used it for another, going over it again.

TH: How unusual, to use it in German, though. I guess it was expected that you would know German.

LP: Yes. I had two years of German at OAC.

TH: But the other students as well would have been...

LP: I had two years of German, two years of French at OAC. Well, scientific German, part of the course at OAC was, of course, in scientific German.

TH: Did you have any trouble in Tolman's classes? Did you have any trouble with the math end of it? You obviously were very intensely involved in the mathematics part of it as well, but did the mathematics associated with the quantum theory at that point in time give you any trouble?

LP: No. That was pretty simple. The mathematics of the old quantum theory, and then, of course, in 1926 when Schrödinger's papers came out, quantum theory began to get the new quantum mechanics. Well, I had a course from Born in 00:53:00December of 1925, I think, on matrix mechanics, [laughs] even before Schrödinger's work.

TH: Oh, really?

LP: I think my notes are up at Corvallis, the notes I took.

TH: Yeah, that's fine. And in 1925-

LP: I didn't care much for that- for matrix mechanics, Heisenberg's attack. Well, I was interested all right, but I didn't see how to apply it to the problems I was interested in. Heisenberg, in fact, hadn't been able to apply his method to the hydrogen atom.

TH: Right, right. Major-

LP: It took a more able [laughs] man in the field of mathematics, Pauli, to treat the hydrogen atom by the Heisenberg matrix mechanics.

TH: My reading of history is that Heisenberg's matrix attack on the problem actually, that because of the mathematics of it, it tended to lose people anyway. I mean, when you say you didn't care for it, was it because it didn't explain things adequately, or was it because the mathematics was obscure?

LP: Well, the... it's much easier to carry out a solution or approximate solution of a quantum mechanical problem by solving the Schrödinger wave equation than to try to treat the problem with matrix mechanics. Heisenberg thought he was inventing this sort of - that's probably what you remember - inventing this sort of mathematics, and Born recognized, or Jordan perhaps, that 00:55:00the mathematics had written a lot about it already, and they called it matrix algebra.

TH: Right, right. The final question, because you've been very patient this morning and I don't want to keep you too long, in terms of trying to understand how the two currents that I see you going through in graduate school, one is the strictly structural crystallography studies that you were doing with Roscoe Dickinson, the work on crystals that you were doing where you were working very hard to determine straight, structural questions from the X-ray data, and obviously the line of thought that had to do with the theory of quantum 00:56:00mechanics and how the two came together. And especially in your post-doctoral years when you went to Europe. At the time that you were finishing up your doctoral work and you were thinking about what to do next, you were sent, and you went on your fellowship. You went and studied with Sommerfeld and worked with the quantum mechanical side of it rather than, say, going to England and working with Bragg or someone who was doing straight crystallography work. Tell me how the decision came about to sort of move in the quantum mechanical direction, I guess, if you would, rather than the strictly structural X-rayed work.

LP: Well, I think part of my feeling - and this may have involved advice, too - 00:57:00was that to go to a foreign country and do experimental work probably means you'll waste a lot of your time. If you do theoretical work, you are just on your own, but all you need is a sheet of paper and a pencil and a slide rule, so that it's better just to study or do theoretical work if you have opportunity to spend a year abroad. Learn things instead of putting in your time trying to build an apparatus that will work and carrying out measurements.

Then, here Sommerfeld had come to Pasadena. I had met him before in Pasadena in 1924, I think. Millikan had invited him to come and give some lectures. And I 00:58:00knew about Bohr, so I thought that - I knew Debye too. I had written a paper with Debye while I was a graduate student, when Debye came to Caltech. But I wrote to both Bohr and Sommerfeld asking for permission to come, in case I got a Guggenheim Fellowship. You were supposed to do that when you applied for a Guggenheim Fellowship. Bohr didn't answer my letter, and Sommerfeld did [laughs]. So, that determined my fate.

TH: [Laughs] almost like going to- like deciding which graduate school to go to.

LP: Yes. I was- I've told you, haven't I, that I was very lucky several times in 00:59:00my life.

TH: Uh-huh. And you consider this one of those times?

LP: Yes. Getting married, meeting Ava Helen, that was one very fortunate circumstance for me. Going to Caltech, I have said there's no place in the world where I could have got along so well in learning the things that it's turned out I have been interested in as Caltech. Partially Dickinson, partially Tolman, but other people too. They had a marvelous faculty already. Dickinson, you remember, was the first Caltech Ph.D.

TH: Right. That's right.

Both: 1920.

TH: 1920, right.

LP: And there were two or three a year, or then four or five. I think there were seven the year that I got my Ph.D. And then, to go to Sommerfeld just at that time, that was an extremely fortunate circumstance.

TH: If you'd like, that's where I'd like to pick it up next time, is when you get to Europe, and talk a little bit more about that in-depth too. Obviously, a fascinating period and a fascinating place to be at that time.

LP: Yes. Sommerfeld, it turned out, remembered me, but it took him several months to remember me. Perhaps two or three months after I had come back, come to Munich.

TH: Huh.

LP: He- I perhaps mentioned that I-well, I mentioned that I had talked with him and that we had walked along together under the arcade by the physics building- [tape ends].