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In footnotes or endnotes please cite AIP interviews like this:
Interview of Linus Pauling by John L. Heilbron on 1964 March 27, Niels Bohr Library & Archives, American Institute of Physics, College Park, MD USA, www.aip.org/history-programs/niels-bohr-library/oral-histories/3448
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This interview was conducted as part of the Archives for the History of Quantum Physics project, which includes tapes and transcripts of oral history interviews conducted with circa 100 atomic and quantum physicists. Subjects discuss their family backgrounds, how they became interested in physics, their educations, people who influenced them, their careers including social influences on the conditions of research, and the state of atomic, nuclear, and quantum physics during the period in which they worked. Discussions of scientific matters relate to work that was done between approximately 1900 and 1930, with an emphasis on the discovery and interpretations of quantum mechanics in the 1920s. Also prominently mentioned are: Max Abraham, Sam Allison, Anderson, Harry Bateman, Eric Temple Bell, Hans Albrecht Bethe, Niels Henrik David Bohr, Bragg, Percy Williams Bridgman, Clark, Edward Condon, Robert Dawson, Peter Josef William Debye, Hobart Cutler Dickinson, William Duane, Paul Ehrenfest, John Ellis, Kasimir Fajans, Ronald Geballe, Samuel Abraham Goudsmit, Victor Guillemin, William Draper Harkins, Walter Heitler, Lloyd Alexander Jeffress, Irving Langmuir, Gilbert Newton Lewis, Fritz London, H. J. Lucas, Edwin Mattison McMillan, Robert Andrews Millikan, A. A. Noyes, Wilhelm Ostwald, Boris Podolsky, Floyd Rowland, Erwin Schrödinger, Allen Goodrich Shenstone, William Shockley, Arnold Sommerfeld, Richard Chance Tolman, Albrecht Unsöld, Gregor Wentzel, Hermann Weyl; California Institute of Technology, Harvard University, Kben︣havns Universität, Oregon Agricultural College, Universität München, Universität Zurich, and University of California, Berkeley.
Perhaps we might begin by talking about how your interest in science began, how your family and friends encouraged you, what other competing alternatives you had for a. career, what plans you had to begin with, and so forth.
Very well. My father was a druggist. I was a boy in Condon, Oregon, a small town in eastern Oregon, and I just put in my collection of newspaper clippings, a clipping saying that a little over fifty years ago there were two future Nobel Laureates in this town of about 1,000 people. [W. P.] Murphy, who did the work on pernicious anemia and shared the prize in physiology and medicine for this work, was in Condon. His father had been the minister of one of the Churches there. I was there and I believe we overlapped, as we discovered when we were talking together last year; we had been in Condon at about the same time. I think he studied at the University of Oregon then, and I went to Oregon Agricultural College. Well, my father died when I was 9 years old and before his death he had taken an interest in my apparent intellectual ability to the extent of writing a letter to the editor of the Portland Oregonian at a time when we had already moved to Portland, asking for advice about what books he might provide for this nine year old son to read or what other actions he might take. I think I have the clipping.
Oh, then it was published.
Yes, it was published in the ‘Letters to the Editor’ column of the Oregonian. There was no mention of science in this letter, but I think that my interest in mathematics was already evident and of course I found myself that scientific questions interested me as a boy. I was always puzzling about various phenomena such as shadows, optical phenomena that I had observed of one sort or another. I can remember lying in bed in my grandmother’s house looking at a picture which happened to be a drawing of a head of Christ. My grandparents Pauling were Lutheran and I attended services, in their house when a minister came and spoke German. Both my grandfather and great-grandfather Pauling, born in Missouri, had spoken German more readily than English I think.
So you spoke German as a child?
No, I didn’t speak German as a child. My father did but this wasn’t carried over into our family. I sometimes listened in on these sermons. But here I was looking at this head of Christ when I saw that a halo appeared above it, a band of light; this of course shocked me. I was perhaps eight or nine years old. I thought, “This is a marvel,” but after a little investigation I discovered the after-image effects or fatigue of the retina and satisfied myself that this was a general natural phenomenon and not connected with the head of Christ.
So we have another instance of how religion has encouraged science! Nay I ask before you go on what sort of response that letter got?
No response, as I recall. Well, if there was an answer by the editor, and it may be that there was a sentence or two, it was not significant enough for me to remember what it was. I may have this clipping but I’m not sure. By the time that I was 13 I had, when I was around 11 or 12, on my own initiative made a collection of insects. I’d gotten a book from the library and had started collecting insects and classifying them, and I had become interested in minerals. Oregon, the Willamette Valley anyway, is not a good place for collecting minerals; agates are about the only thing that you can find and perhaps some zeolites. I was not successful as a collector but I got a book from the library on mineralogy and I copied out tables of properties, hardness and various properties, onto sheets of paper and glued the papers to the wall in my workroom. And about this time I had developed an interest in chemistry. When I was 12 I had a course in high school, my first year, in what was called “physiography”, which was general science. This interested me very much. I can remember the teacher, an old woman, about 24 I suppose; she’s still alive in Oregon, and her name is Geballe, G-e-b-a-l-l-e. Two of her nephews are pretty well known physicists, one at Berkeley and one at Brookhaven. That’s the next generation down. I can remember her telling what flint was, and jasper, and this of course was related to my interest in minerals which I think had already been developed. I can remember her carrying out an experiment to show the pressure of the atmosphere. She had a Log Cabin Syrup can with a little water in it. She boiled the water for awhile, screwed the top on, and. then let it cool and it collapsed. And I remember other things that I learned in this course. Then, when I was 13 years old, I was walking home from high school with a fellow named Lloyd Alexander Jeffress who asked if I would like to see a chemical experiment or two. I said yes. Chemistry had been left out of the physiography course.
He was a fellow student?
Yes, a fellow student a few years younger than I. I stopped at his home and went to his bedroom with him where he carried out certain experiments; he mixed potassium chlorate and sugar, putting a drop of sulfuric acid on it which started the reaction liberating water and producing carbon. Very exciting.
Yes, that is a very striking experiment. I remember that one.
He did some other experiments and I became a chemist then. I built a little laboratory in my basement. I found that there were bottles of chemicals in the small chemical laboratory of the Oregon Iron and Steel Company smelter which hadn’t been operated for 15 years perhaps, or even more. The roof had fallen in in this building where these bottles of chemicals were. I, from time to time, “borrowed” them and took them to Portland; this was in Oswego which involved going seven miles. My grandparents lived there and my grandfather worked for this company as night watchman so I had access. He was night watchman at the foundry which was an eighth of a mile away and the smelter was just abandoned. It’s no longer there; it’s been torn down. So I had a supply of chemicals and I became a chemist. Lloyd Jeffress shifted from an interest in chemistry to electrical engineering when we went to college. Let’s see — was he a year after I was? I’ve forgotten. When we went to the Oregon Agricultural College he spent the whole year doing physics experiments instead of studying electrical engineering. Then he shifted to Berkeley as a physicist and after a year became interested in medicine, spent a year studying anatomy and other pre-med courses and then became interested in psychology, got his PhD in psychology and became the head of the psychology department at the University of Texas. He spent one year here at my suggestion. I was a member of the (Hickson) committee which decided to arrange a symposium on cerebral mechanisms and he was brought here to arrange this symposium which he did and he edited the book, Cerebral Mechanisms. Well, so there was no doubt about what I would do, except some lack of understanding on my part. I received my bachelor’s degree in chemical engineering because my circumstances were such that the only career that I knew about associated with chemistry was that of chemical engineering; however, a few years later I remembered my grandmother [having asked] what I was going to do — I was perhaps sixteen then and perhaps my first year in college — and I said I was going to be a chemical engineer. Lloyd Jeffress said, “No, he’s wrong in saying that. He’s going to be a professor.” He knew, at the age of about 15 or 16. He said, “He’s going to be a professor.”
He’d have had difficulty predicting his own outcome probably.
Yes, at that time, or he might have said that he was going to be a professor too.
Did you use books when you were performing these experiments? Did you precisely repeat them?
Yes, I found a book. There weren’t very many books in our house — my mother had difficulty getting along too, you know, after my father’s death — but there were several books including one book on chemistry by (Williams), I believe, and that has been lost so far as I know. I don’t have it. This was the principal book on chemistry that I had although I don’t know anymore what was in it. Then I had the U.S. Pharmacopoeia and the U.S. Dispensatory which my father had had and I read these; I read a great deal in these.
Did you have his apparatus?
No, I didn’t. I got some from the Oregon Iron and Steel Company and I bought a little bit. A neighbor, an old fellow also encouraged me to study Greek by myself. I was studying Latin in my college preparatory course but I was interested in Greek and this old man who was retired from his position as climbing guide on Mt. Hood, was a Greek scholar and gave me a. number of Greek books and helped me to study Greek.
Did you gain any facility at it?
No, I had the equivalent of perhaps about a year of Greek, but by study by myself. I can remember studying Greek as I rode 25 minutes on the steam train the seven miles to Oswego to see my grandparents, which I did nearly every weekend. He also had a job after he retired as stockroom keeper at the — I’ve forgotten what it was called — Pacific Northwest School of Dentistry, let’s say, and he gave me a good bit of apparatus, somewhat broken or chipped test tubes and flasks and things like that. Then a man, Mr. (Zigler), who had been a drug salesman [also gave me chemicals]. My father had worked several years around the time that I was born, as a salesman for a wholesale drug company, (Skidmore) Drug Company, travelling around by horse and buggy in the various communities within a hundred miles or so of Portland. This other man, Mr. (Zigler), who had been a salesman probably for the sane firm and then later manager of one of the stores also provided chemicals for me. One of the first chemical operations that I remember, and this preceded my interest in chemistry, before I was 13, was using some potassium cyanide that he gave me and some plaster of Paris to make a killing bottle for insects. I put the potassium cyanide in the bottom of the bottle and covered it with plaster of Paris in the approved manner. This was before the days of chemical sets, but I fooled around quite a bit and I continued to be dissatisfied all of my early years with the fuzziness of chemistry, the vagueness of chemical ideas, their lack of quantitative character and the difficulty that I had, despite my being a good student, in understanding chemical phenomena such as the separation schemes in qualitative analysis. This puzzled me, but over and over again I returned to the theme of understanding chemical reactions. When I was 18, I believe, in 1919 at the end of my sophomore year, I worked for a month delivering milk. A very hard job, working eight hours a night every night from about eight o’clock to about four o’clock with a horse pulling the milk wagon and delivering milk to about 500 customers. The first week I learned the route and I found this interesting and then the other three weeks were almost intolerable for me and probably a little hard on me physically, too. I really was in bad shape at the end of a month; I had agreed to do it for at least a month or not get paid and I held out for a month. I had applied for a job as Paving Plant inspector to a man who had a contract with the State of Oregon to inspect the blacktop pavement that was being laid, the bituminous pavement, and I was rejected when I applied. That was when I took the milk delivery job. I was rejected but at the end of the month I think I had a call from him; he had had so much difficulty getting anybody that he had to scrape the bottom of the barrel. He took me on and I worked at this for five seasons, one year for him and then for the State of Oregon, that took on the job itself for perhaps three years; and for the (Warren) Construction Company one year. These were summer jobs, but the first summer I worked about five months at it. I can remember while I was a paving plant inspector going through the rubber handbook and tabulating the properties of substances; in particular I remember tabulating the magnetic properties — diamagnetism, paramagnetism, values of magnetic susceptibility — and trying to find some explanation of them. I knew nothing of Langevin’s contributions, nothing of Weiss; I had no idea about induced currents responsible for diamagnetism. I was attacking this in a purely empirical way with the basis being a possible correlation with the periodic table.
Just on the basis of the numbers.
Yes. And of course this is the sort of attack that I have continued to apply to scientific problems. I like to take a very complicated subject where there is no order, such as immuno-chemistry or immunology as I did in the late ‘30’s and think about it for a long enough period that I can find some way of introducing order into it.
But you weren’t so successful with the magnetic properties.
No, I didn’t discover anything, and as a matter of fact it wasn’t until 1922 that I learned what the explanation of diamagnetism was, when I was a graduate student.
I meant to ask you what kind of physics and chemistry you had at Oregon.
Weil, in high school I had one semester of physics with Millikan and Gale taught by a good smart fellow and I liked this course. Before taking the course, I had studied chemistry for a year and in fact I received credit for a second year of high school chemistry. I worked on by myself in the high school laboratory under the supervision of the teacher. I had carried on some organic experiments, organic preparations, and did some work in qualitative analysis. I assisted him in making measurements of the heat of combustion of samples of oil and coal that were purchased by the Portland schools. He had the job of checking that, and I stayed after school and helped him on that. My high school chemistry course was I think very good and I learned a good bit from this extra year too. Then at Oregon State I took regular freshman chemistry, the course given to chemical engineers and mining engineers. They were lumped together and constituted the School of Mines.
Did that bore you at the time?
No, it didn’t bore me. I had apparently a mind of my own and I began attending the lectures but I wasn’t too pleased with the man who was giving the lectures. Then I noticed that there was another course in chemistry being given, I don’t know to whom, with another man giving the lectures. I just went in and listened to his lectures and then I asked for permission to attend his lectures instead of the ones that I was supposed to attend. This probably made somebody angry which never occurred to me. I was much impressed by this man who was an able, vigorous and effective teacher, Renton Kirkwood Brodie. He became Vice President of Proctor and Gamble. He left that year. I didn’t see him then for some forty years and I was pretty disappointed when I did see him after this long period when he had been with Proctor and Gamble. Quantitative analysis, which I had during my sophomore year, interested me very much and at the end of my sophomore year I delivered milk for a while, as I told you, and then had a job as paving plant inspector. I didn’t return to Oregon State because I didn’t have enough money. I had given my mother the money that I had received — 125 dollars a month was my salary — and my expenses were small because it was in southern Oregon in the mountains and I lived in a tent where the workmen lived. This was provided by the contractor and I just ate at the mess there, so I sent the money to her and at the end of the summer she told me that she just couldn’t pay it back. Then along about the first of November I received an offer of an appointment as full time assistant instructor in quantitative analysis at Oregon Agricultural College to teach the sophomore course that I had just been taking the year before.
That you had just finished!
Yes. That was only 100 dollars a month, but I accepted the job and spent the year teaching quantitative analysis full time. In fact I would consider now that by present standards it was several full time jobs. I had about 40 contact hours per week. You know, there’s a lot of laboratory but I gave the lectures too. That’s how I conducted the classes. After about the first month perhaps, or even earlier, I was conducting the classes.
Did the professorial life appeal to you after that?
Well, I don’t know that it did but I suppose so, without my recognizing it. I don’t know when I began to feel that I was going to be a professor, I just don’t know. It came gradually enough. Perhaps I just accepted it that time a year or two earlier when Lloyd Jeffress had said I was going to be a professor. Maybe. Well then in college I had one year of engineering physics using a textbook called Engineering Physics or — I’m not sure, but it was probably all right. This was pretty simple physics and was the only course I had. I think it was during my sophomore year rather than my freshman year that the physics course came along. The chemistry was all right, I would say, for those days, the courses in chemistry that I studied: organic and analytical and general chemistry I put in time on industrial chemistry which was rather a waste of time but it didn’t bother me much. It’s too bad that I couldn’t have studied a little more physics. There was a period of four years out of five — I was there five years, the one year teaching — when I studied no physics, and there was a period of three and a half or three and two-thirds out of the five years when I studied no mathematics. In my three and a half years of high school I had studied four years of mathematics including trigonometry and college algebra and I was then able to register for calculus my first year, although it was a sophomore subject; and the same year I took a course in analytical geometry.
Then the only remaining course in mathematics that was taught was one in differential equations, a simple one-term course in differential equations which I got through. There was a long period then when I did not have the opportunity of studying mathematics in a class and I didn’t know enough to study by myself. It wasn’t until I came to Pasadena at the age of 21 in 1922 that I was able to study vector analysis and modern analysis, Whittaker and Watson. I had Harry Bateman teaching the course in vector analysis and it was quite a course. Every once in awhile he would get off on something none of us could follow. “Bob” [H. P.] Robertson was a classmate of mine. He was a year behind me in graduate school but he was in this course. I think it was his first year here and my second year. Then of course I attended other classes in mathematics here, integral equations — I think Bateman gave a course on differential and integral equations. I didn’t get very much out of this. He gave a one term course on Newtonian potential theory and this I found extremely valuable. It had a lot of stuff in it that he had developed himself I think, material that was hard to find in the literature or in textbooks anyway.
Before we get to Cal Tech, though, there are one or two things I’d like to ask about Oregon. One of them is about the chemical theory you were taught if you were taught any chemical theory at all. Did. the problems of the bond come up or chemical combination in general?
The chemical bond was taught on the ‘hook-and-eye’ basis and I can remember that I was asked, perhaps when I was a, junior, if I would give some lectures in the evening for students who were having trouble in freshman chemistry and perhaps 50 of them attended these lectures. But I can remember presenting chemical bond theory on the ‘hook-and-eye’ basis myself.
No electron structure whatsoever?
No. However, this year when I was a full time teacher my office was the chemistry library that no one ever went into except that the secretary of the department had her typewriter in there and she taught me to type with the touch system. I didn’t have much time to be in the office anyway, but still it was in the chemistry library and I ran across the papers by Langmuir which were published that year. I think I even dug out the paper by Lewis, the 1916 paper. At any rate I was very impressed by this work on the electronic structure of molecules or ideas about shared electron pair bonds and it may well be that that was the start of my interest in chemical bonding. While I was in Oregon State, my senior year I suppose, there were a couple of chemistry seminars held. One of them I think was on the chemistry of fish by a member of the staff who has become an authority on fish. Of course there was the Agricultural Experiment Station there; he may have been associated with it. The other was on the nature of the chemical bond, by me — ideas about chemical bonding. Well, I just don’t remember this seminar but I have come across an announcement of it which I have somewhere in my files, or perhaps in my scrapbook there is this announcement that I was giving a talk on molecular structure.
So that was really the first time you had run across the electronic bonding at all, in the Lewis-Langmuir theory.
Yes. I’m pretty sure I didn’t know anything about Lewis’ 1916 paper; it was Langmuir’s papers in 1919. I was 18 years old and I don’t think anybody had ever mentioned these ideas in a course. I think it was that I happened to run across these papers.
Have you any idea what the general situation was at that time?
Well, it’s pretty clear that in Berkeley there was lively discussion of these things going on and probably essentially nowhere else. In Munich of course there was a little in that — who was that German who published the paper about the same time?
Kossel, yes. He was in Munich I believe at the time he wrote that paper. He has been in Kiel since then; he may have died by this time.
Yes, he is dead.
Well, I doubt that there was very much discussion of his ideas. There were other people of course who talked about electronic structure of molecules. J. J. Thomson had his ideas. [There were many] people who weren’t in Berkeley and. there were so many there that I don’t need to start listing them. You know about them anyway. The man with the spinning electron in Berkeley; he anticipated —.
A student of Lewis —.
I’ve forgotten his name too. The head of the department at Chicago, had ideas about electronic structure. There were quite a number of people in those early days, but I think the Berkeley group was the only really active one in the field of the electronic structure. Parsons was the man’s name. I remember looking up his paper in the Journal of the Faraday Society, not the British but the Philadelphia. He had some sort of ring electron.
You graduated then as a chemical engineer and then you turned up at Cal Tech. How did that occur?
During the year between my sophomore and junior years a notice came from California Institute of Technology announcing graduate fellowships, teaching fellowships I think they were called then. The head of the department at Oregon State who was supposed to be in charge of quantitative analysis teaching, and whom I was helping get out the grades — or he was helping me by signing, his name to the grade sheet or something like that — said, “Perhaps this is something, you ought to be interested in.” And, in fact, I wrote to A. A. Noyes saying that I was interested but that I was only a sophomore and moreover didn’t have any money and I would need to have a job. During my freshman year I put in good and had odd jobs; my main one was that I chopped wood for the cook stoves in the girls’ dormitory and mopped out the kitchen and so on. I worked a hundred hours a month and good hard work, too, and during my sophomore year I was in charge of the solution room in the chemistry department. I made all the solutions to put on the desks and made the unknowns as well and did all sorts of things. During my junior and senior years I was assistant in mechanics and materials; I corrected problems in statics and dynamics, strength of structures, bridges — you know just engineering statics and dynamics. I also helped in the strength of materials laboratory with tensile strength stuff and that sort of thing. I’d had the course as a junior and I think assisted to some extent as a senior. But also during the second and third terms of my senior year I handled a section of freshman girls, home economics girls, so I kept busy there in one way or another and had connection with the department of chemistry. I wrote then to A. A. Noyes and received a letter from Stuart Bates, Professor of Physical Chemistry here, who is dead now, saying that there couldn’t be any commitment about my earning my way as a junior and senior and moreover even after they got acquainted with me there would be difficulty in my getting a job that would support me. Well, that was the end of that for the time being. In the spring of 1922, my senior year, I wrote to half a dozen universities about graduate work. An important part of this [concerned the fact that] my mother had not wanted me to start in as a freshman; I had some difficulty in using the money that I had earned working in the machine shop that summer to get started at Oregon State. She was having a lot of financial problems and thought that I was doing so well in the machine shop, where I had started at 50 dollars a month and received 75 the first month. I think it got up to 100, and I was offered 150 if I would stay. This seemed like a lot for a 16 year old boy.
To give up to go to school.
Yes! It seemed like a lot to my mother and it was a lot, you know, but I was a good apprentice machinist; I didn’t make mistakes. So I succeeded in going to college although I missed out on going this one year and I was determined to go to graduate school too. About I think my last two years there was a man there as professor of chemical engineering, head of the department — he was the department — who had quite an influence, although this statement by Fulton, the head of the chemistry department, indicates the idea of going on to graduate school. I think at that time I thought, “Well, I should get a master’s degree.”
This was to continue in chemical engineering.
No, I don’t think so. I was thinking about chemistry then; at CIT the fellowships wore for Graduate work in chemistry. There was chemical engineering here, too, but not much graduate work at that time. They were giving PhD’s in chemistry, the first one in 1920 to Roscoe Dickinson, the first PhD from the institute.
He remained here then, didn’t he?
Yes. He had started his graduate work at NIT but had come with Noyes here doing x-ray defraction and he remained here until his death. This head of the department of chemical engineering fat Oregon State], a man named Floyd Rowland, had got a PhD at the University of Illinois in chemistry. I think he may well have had difficulty in getting his PhD; it took five years and he wasn’t a very brilliant person by any means, but he was an extreme enthusiast about graduate work and he lent money to students — he never lent any to me — I borrowed money from John Fulton, the head of the chemistry department — but he encouraged people to go on. In the class I think there were fourteen people who graduated in chemical engineering when I did and I would say eight of them got PhD degrees. I was one, Paul Emmett, who is probably the leading authority on adsorption; he’s the editor of a several-volume work on adsorption and is head of the department of chemical and gas engineering at Johns Hopkins and a very able man. Then several others that I don’t need to list because they are all chemists, but good chemists.
There was a degree in chemistry, though, given by Oregon?
No, just in chemical engineering. He encouraged people to go somewhere else to get PhD’s and Paul Emmett and I came here and others went to Wisconsin, Illinois, MIT and various places. It may be that if it hadn’t been for Floyd Rowland, I would not have gone on for graduate work. So far as I know he’s still alive; he’s had a rather checkered career but he’s still alive. One of his proteges is a well-known TV fellow who has a program called “Open End” or something like that in New York. You don’t know? Well, I’ve forgotten his name. He told me when I was on his program that he would never have amounted to anything in Boston if it hadn’t been for Floyd Rowland. I don’t know what his job has been after he left Oregon. So I applied to a half a dozen colleges. I had a letter from Harvard saying that there was no appointment that they could offer that would permit me to take full time graduate work but they could give me a half time instructorship that would allow me to get a doctor’s degree in five years perhaps. For the amount of money it didn’t seem likely — well, it wasn’t a very good sum, so that was the end of Harvard. I had a letter from the California Institute of Technology offering me a fellowship which I accepted and I then wrote to Berkeley and the other schools withdrawing my application.
Berkeley hadn’t answered?
Berkeley hadn’t answered.
Which would you have preferred?
Well, it’s hard to say. I think it wouldn’t have been any mistake to have gone to Berkeley. I was fortunate, I think, in not receiving the Rhodes Scholarship. I was nominated for the Rhodes Scholarship by Oregon State the first year that Oregon State was allowed to nominate anyone; Paul Emmett and I were the two nominees and we weren’t awarded, neither one of us received this. Well, I think it was just good luck.
But that wasn’t clear to you at the time!
No. I found that there was a man at Oxford, and I haven’t been able to identify him since then, who was interested in the structure of alloys, inter-metallic compounds, and. this was an interest of mine already then. It’s continued to be an interest of mine. I wrote to him and had a letter back saying that his college would be willing to accept me and I put this down as what I wanted to do, but as I say fortunately I didn’t get the Rhodes Scholarship. So I came down here and got to work.
You started doing a good deal of your structure of crystals immediately, didn’t you?
Yes, that’s right. At Oregon State I had worked on a research problem of my own. I was interested in magnetism and I had an idea which was that we should be able to learn something about magnetism by depositing crystals of metallic iron out of an aqueous electrolytic solution of an iron salt in a magnetic field. I got a big magnet and set it up and built an apparatus and tried depositing iron; to determine the orientation of the crystals I polished them and etched them and looked at them under the microscope. Well, this wasn’t a very well thought out experiment and I didn’t get anywhere, but it gives an idea of what my thinking was. When I got here I immediately began work on determining the structure of crystals under the tutelage of Dickinson and of course I immediately too began trying to understand the structures of crystals. I began tabulating ail of the structure determinations that had been made and the inter-atomic distances and began trying to understand the inter-atomic distances.
Again trying to bring them into some kind of coherence with the periodic table?
Yes, to be sure, and thinking about the question of ionic crystals and covalent crystals and wondering about sizes of ions and the forces of attraction between ions.
Had you done that at all at Oregon? Was it a big change in your interests?
Well, A. A. Noyes had written to me in the spring after I had received this appointment, suggesting that I might like to work on the structures of crystals in view of the interests that I had described in my letter to him, and recommending that I read the Bragg book. I got this from the Oregon State Library, I got it on loan from Salem, and I read this book and that was a start. I had an interest in crystals already from when I was twelve years old, say, and began trying to understand mineralogy.
What about physics here?
Most of my graduate courses were physics courses, or essentially physics courses, taught by Tolman. There wasn’t much given in graduate courses in chemistry. During the summer before coming here I worked all the problems in the first nine chapters of Noyes and Sherrill, a book in physical chemistry. My course in physical chemistry had been a very poor one. Then for one term I had a course from A. A. Noyes himself — the last course that he ever taught — on thermodynamic chemistry which was the last four chapters of Noyes and Sherrill, which was their new book then. I studied chemical thermodynamics during that first year with Tolman, I believe, as the teacher, from a book that had just been published that year called Lewis and Randall. I also had a course from Tolman on the basis of science.
Do you recall what he had to say about that?
Oh, he discussed extrinsic and intrinsic properties — perhaps he didn’t use those names. He discussed the theory of relativity a little, and the theory of relativity of size, if you know what the theory of relativity of size is.
Well, I’m not certain I do. What is the theory of relativity of size?
Well, the theory of relativity of size is something that Tolman had worked out that was related to what Lewis had proposed, called the theory of ultimate rational units.
Yes, that’s what I thought it might be.
There’s a relationship here. Tolman attempted to find some arguments based upon what he called relativity of size that would enable him to account for the values of the physical constants. Well, this was a rather mystical part o± the course in a sense, but much of this course I found pretty interesting. And then perhaps the next year there was a course given in the chemistry department that used Foote and Mohler as the textbook and it may have been that that was even the first year. I’ve forgotten. Then along about that time there was a course, in the chemistry department too, using Sommerfeld’s Atombau und Sektrallinien.
In the chemistry department.
Yes. Now in physics and mathematics, let’s see. I never took [W. R.] Smythe’s course in electricity and magnetism. I had instead that Bateman course on Newtonian potential theory, which I liked very much. Then the various mathematics courses that I have mentioned to you. I think I took a course from Millikan called ‘kinetic theory’ but I may have dropped it. Millikan was getting sort of haphazard in his teaching at that time. I started a course on thermodynamics with Epstein which became his book on thermodynamics and he called me in or came to see me and said he thought I’d better drop it since I wasn’t coming to the lectures. Well, you see I had studied chemical thermodynamics anyway in Lewis and Randall and probably I just wasn’t finding much new.
Was it required that one attend lectures?
No, I don’t think there were any requirements about attending lectures in graduate courses, but the chemistry department, the division of chemistry and chemical engineering — you know we don’t have a chemistry department but just a division — instituted a rule that a man who had a graduate assistantship or teaching fellowship could register for forty-five units and not more [less] than twenty-two and a half — this is three times the ordinary; the units represent total hours rather than class hours or a third of the total hours of lab the way ordinary semester hours do. Forty-five units is a full week’s work; fifty-four units, say, is the maximum a student is allowed to register for, and a graduate student on an appointment was according to this rule allowed to register for only forty-five and half of this must be research. Well, when I was a graduate student this rule was not yet in effect and I would register for forty units of classwork and twenty units of research, say, and then perhaps put in more than twenty hours a week on research because the classwork didn’t take me so much time anyway. So the students here were tempted to register for a lot of courses; there were such good courses around. I had probably registered for as many graduate courses in physics and mathematics as the PhD students in physics did. I liked these courses. I was eager to learn physics and mathematics and there were good courses. Then Tolman gave his course in statistical mechanics and it was really an excellent course; I learned a great deal from that. That was probably my second year as a graduate student. Then my third year as a graduate student I wrote a paper with Tolman, one of my papers, on the residual entropy of crystals in super-cooled liquids at the absolute zero [“Entropy of super-cooled liquids at the absolute zero,” J. Amer. Chem. Soc., 47, 1925), which clarified this point. Eastman up at Berkeley had written a paper saying that complicated crystals should have some residual entropy and we pointed out that —. This started by my giving a seminar in which I said that complicated crystals should have zero entropy at the absolute zero unless there was disorder, and that super-cooled liquids had disorder and that we could describe this disorder as R log aN.
You had already worked out that dependence?
Well, I wouldn’t say that I had worked it out. I just wrote it down, you see. This is the way I usually do things and Tolman was interested and said, “Well, this ought to be looked into carefully; why don’t you read Ehrenfest and Ehrenfest?”
His Encyclopedia article?
No. They had a paper — I don’t remember just what it was any more—but they had a paper that was pertinent here and that provided the basis of our discussion. “Entropy of Super-cooled Liquids,” Ehrenfest and Trkal; I guess it’s Ehrenfest and Trkal rather than Ehrenfest and Ehrenfest. This was a paper on quantum weight, you know, on hN, and you see we say glass is to be regarded as a quantum system with its degrees of freedom in the next-to-the-lowest quantum state. This was written before quantum mechanics. It’s not a quantum mechanics paper. It just came at this time.
What did Tolman contribute to this?
Well, I don’t know. I think I wrote a version and then he wrote this version. I remember his asking what he [I] thought the order of our names should be, and I said I thought my name should come first. So it did.
In fact it did.
Afterward I’ve thought that’s rather interesting. But I can remember this. He referred me to Ehrenfest and Trkal, and my memory is that both he and I worked out to the arguments giving the R log a at the same time. Of course I think that already at that time my feeling for structure was better than his. For two years and a half before this paper was written in 1925 I had been working very hard trying to understand the nature of crystals especially.
This is your first non-crystal structure paper, isn’t it?
No, I think that with Debye.
Is Debye before that one?
It was before that, and the inter-ionic attraction theory — August, in the same issue, actually. They were both in the August issue of the Jour. Chem. Soc. Or was it earlier?
April 15, that Debye one is dated, and the other is April 23, so it just preceded. How did you happen to write the paper with Debye?
Well, A. A. Noyes had been working for 25 years on the structures of ionic solutions, electrolytic solutions; and when I came down here he was just preparing some papers on properties of electrolytic solutions. The paper by Debye and Huckel came out at about this time, so there was much interest here. A. A. Noyes, you know, in 1904, had said that there is plenty of evidence, as pointed out by Arrhenius, that solutions of salts are only partly ionized, but there is also evidence — Beer’s law for example and (Kolordman’s) that they are totally ionized; and what is the explanation? Well, he said, an Englishman named [S. R.] Milner had given the explanation. You know, Milner had calculated the free energy by summing or attempting the summing of the — well just by statistical mechanics and by a laborious method, back about 1911. So he was writing a paper about Milner’s calculations in relation to the properties of ionic solutions when Debye’s paper of April 1923 and Debye and Huckel — also 1923 — came out. And Noyes then wrote a couple of papers on the Debye-Huckel theory and gave them to me before sending them in. Well, I found a lot of things to criticize in them, and I did point out some statements Noyes had made in them that I thought did not apply really to the theory, and he changed that. But I thought, why not do a better job, make the theory applicable to concentrated solutions? So after some months of hard work — in addition to my experimental work, working in the evenings — I worked out a theory which has never been published. I think it was really a pretty good job. I have always been sorry that it wasn’t published.
Why wasn’t it?
Well, Noyes asked Debye, who was in the eastern United States, to come out here for a couple of weeks and give a seminar and to talk with me about it. When he came, I presented the theory to Debye, Noyes, Tolman and perhaps a couple of other staff members — not a regular seminar, just presenting it to them — and Debye just didn’t say anything. He said to me then later, “Well, why don’t you work out a little idea that I’ve had to investigate the dielectric constant.” Well, this was a simple, routine job. And he also said to me, since I did this in a couple of days — and you knew he knew what the answer was; this was just satisfying A. A. Noyes, I think — he said, “Why don’t you work out the frictional resistance, or the (caphoretic) velocity of a liquid droplet in a fluid medium, in which you have the notion of the liquid within the drop as well as around the drop?” A pretty hard problem. I worked hard for a couple of weeks on that and showed my results to Debye, and he just didn’t pay any attention to it. I just don’t know; hydrodynamics is not my field. I don’t know if I still have those papers or not, but I’ve never found out about that. Then I went to Europe on my Guggenheim fellowship; and while I was there, Dr. Noyes wrote to me about this paper which I wanted him to submit for publication. Here is something from Dr. Noyes’ file; after his death this came to me. [From Pauling to Noyes]: “I am returning separately two copies of my paper on the inter-ionic attraction theory. It is long, but I feel that its length is required in order to make it understandable, for it is not padded and I think nothing extraneous is included. I should be grateful if you’d read it, make any changes and corrections you deem advisable and have it sent to Professor [A. B.] Lamb if you think it is in shape for publication.” Well, I don’t seem to have the answer to this; I may have it somewhere. But the answer was that he and Tolman had decided that this paper shouldn’t be published as a contribution of the laboratory. Of course I was free to submit it myself if I wanted to. Weil, this discouraged me so much that I didn’t ever submit it. I presented it actually at the American Chemical Society meeting in Los Angeles in 1925, but it never was published.
You couldn’t get past that barrier — or didn’t feel inclined to?
I didn’t feel inclined to, and perhaps this was the right decision because it involved something a little tricky on my part. I don’t know; I probably could develop a better argument now than I had then for what I did. I. evaluated the potential in two ways that represent extremes, and then I said “Well, I don’t know Just what the correct value is, but I’ll take the value mid-way between these two extremes and put it in the correction terms.” There were two things involved in it — two problems — one of them I handled in that way; the other I handled just in the straightforward way of an expansion and numerical evaluation of the terms in the expansion. I’ve always been sorry that I didn’t publish that paper.
I can see.
So I was doing other things than crystal structure. I was attacking theoretical problems of whatever sort came along.
What about the discussions of quantum physical problems? You say that Atombau was studied in the chemistry department. And apparently you didn’t have much to do with Epstein; didn’t take his seminar, for instance.
No, I didn’t attend his courses; but I did always attended the physics seminar and the physics and astronomy club which met alternately at Mount Wilson Laboratory — up here on Santa Barbara Street a mile away — and here; and I attended the chemistry seminar. In all of these seminars there were discussions of new fields; for instance, Millikan and [I. S.] Bowen would discuss their spectroscopic results. There were papers presented. As soon as quantum mechanics was discovered, I heard about it. Eckart was here. Eckart carried out his proof that wave mechanics and matrix mechanics are equivalent — you remember he did that independently of Schrodinger. Before that time, for example, Ehrenfest was here and Sommerfeld.
Yes, so was Darwin, I believe.
Darwin, yes, I had a couple of courses from Darwin during the year he was here, which was my second graduate year.
‘23 to ‘24, I believe; the whole year.
Do you recall discussions of the central quantum physical problems like the Compton effect and the Stern-Gerlach experiments?
Oh, yes; I remember when the Compton effect was carried out and when the experiment of Compton and — what was his name, not Wilson but one of his students — in which they got a time correlation.
Oh, yes, the ‘anti-Bohr-Kramers-Slater’ experiment. Wasn’t it Simon?
Compton and Simon, yes; I think that was right. Tolman and Ehrenfest were working on weak quantization. Ehrenfest had thought up a lot of paradoxes. “If you have a pendulum hanging on a quartz fiber and you spin it, what is the cycle of the motion?”
He invented that one somewhat earlier, I think.
Yes, but it was still under discussion. He presented it in his seminar. You see I wrote my paper on — there was a question of half quantum numbers coming in, and I worked out the dielectric constant of a diatomic gas in a magnetic field and showed that there was a difficulty there with the half quantum numbers. But this didn’t get published until after quantum mechanics had been discovered. I think I may have presented it in a Physical Society meeting. So I was puzzling about this. Sommerfeld came here in 1924, say, and while he was here he had word from Heisenberg that he had discovered matrix mechanics.
He was here in ‘24?
Yes, ‘24 or ‘25.
It must have been ‘25, because Heisenberg’s paper wasn’t published until mid-‘25.
Yes, well, it was probably spring of ‘25, then, although I thought it was ‘24 already. It may be that I am confused. I remember Sommerfeld’s saying that he had a brilliant young student who had just written him that he had solved a problem.
But it probably wasn’t —
It probably wasn’t matrix mechanics; it may be the hydrogen molecule. He was working on the hydrogen molecule problem, and then this would have been erroneous.
Yes, it was probably some other matter.
But while Sommerfeld was here, he emphasized very strongly the anomaly of the inner quantum number and the outer quantum number — well, at least he talked about the inner quantum number and the outer quantum number.
What is the outer quantum number?
Well, you have — how do you describe the spectrum of sodium, for example? Nowadays we say well, there is a 3s level for the electron and a 3p level and a 3d level, and the difference in energy of the 3s, 3p and 3d represents — well, I’ll say what Sommerfeld said. The difference in level of the 3s, 3p, and 3d represents a difference in the degree of penetration of the core, the inner shells, that is due to the different eccentricities of the elliptical orbits, 3s, 3p, and 3d. But you also have fine structure, the 3-P1/2 and 3-P3/2 — of the doublets, the doublet P1/2 and doublet P3/2 — and this is a relativistic correction in mass that depends on a difference in eccentricity of the doublet P1/2 and doublet P3/2, of the orbits. So that in the first explanation of the s, p, d separation, you say that the p levels have a certain eccentricity different from the s and the d. But then in the relativistic fine structure, you say that P1/2 and P3/2 have different eccentricities.
Yes, it was always a difficulty.
So that they introduce an azimuthal quantum number; in fact, they introduce two azimuthal quantum numbers and then in talking about the s, p, d separation you use one and in talking about the fine structure splitting you use the other. And the question is how can you have two quantum numbers that describe the eccentricity of the orbit? It only has one eccentricity. So this was brought out, and my memory — I have to change my memory. Sommerfeld just talked along glibly about the inner azimuthal quantum number and the outer azimuthal quantum number without giving anybody, any auditor, any impression that there was anything funny about it. But Millikan and Bowen wrote a paper and presented a seminar saying, “Here we have a great puzzle — how can you talk about two azimuthal quantum numbers, the inner one and the outer one?” This was in connection with their work in the ultra-violet — their spectroscopic work. And my feeling was, “Well, it is a great puzzle; but it’s too great a puzzle for me to worry myself about.” I hadn’t yet reached —. I puzzled about chemical problems and to some extent about quantum mechanics; for example, this simple one about the influence of a magnetic field on dielectric constant of a gas where I showed that you’d get the wrong answer from the —.
Well, that’s not such a simple problem. In the old quantum mechanics, that’s a pretty elaborate calculation. I’ll want you to tell about that a little later on; but at present, do you recall what Sommerfeld retorted to this?
Well, I don’t think Millikan mentioned this while Sommerfeld was lecturing. These were two different seminars that I’m talking about. But you see there was a lot of lively discussion going on. There was much discussion here about the Compton effect and what its significance was. When an old physicist at Columbia wrote a paper, Davis isn’t that his name, Davis?
Duane? The debate with Compton?
Yes, but I’m thinking of another paper. Davis, I think his name was. He wrote a paper on a quantum explanation of the Bragg diffraction.
That was Duane. You mean where he has a photon explanation and you exchange momentum with the crystal lattice? Yes, that was Duane.
Yes. I think that I gave a seminar on that in our chemistry department here. You remember that Epstein wrote a paper in which he derived the whole of diffraction theory from the old quantum theory just by this transfer of momentum —
That was with Ehrenfest, wasn’t it?
It may be Epstein and Ehrenfest; I don’t think I have any references. I may have in the Introduction to Quantum Mechanics if I have a copy of that book. [Goes to get it] I was pretty angry with Tolman, in that when I gave this seminar — I believe it was I who gave this seminar — Tolman said to Dickinson, “Now, here you are working away determining the structure of crystals. Why didn’t you do this job that Duane did? That’s something worthwhile.”
He said that to Dickinson?
Yes, well, this irritated me that he would speak this way to Dickinson. [looking in book] Yes, Epstein and Ehrenfest, 19214. Yes, that was 1923, Duane. This irritated me, and I was even more irritated later on when I thought, “Why didn’t I go on and do the next job, or why didn’t I think to mention it to Tolman at the time?” But I never did mention it to Tolman that the next job was to use exactly the same argument that Duane had used but with an electron. And I did put it in my lectures as soon as I thought of it, and then put it in this book. You transfer momentum and you get —
That would have been something.
That would have been something. [Laughter]. That was a lesson to me when I finally got around to realizing several years later, five years later, say, —
What one could do with that idea!
Yes! The de Brogue wave length of the electron comes out very simply. But there was a great deal of interest in the development of quantum theory here. And as soon as quantum mechanics was discovered, Born came and lectured here. I attended his lectures on matrix mechanics. Then, of course, I was fortunate to attend, I think the first lectures, that Sommerfeld gave on wave mechanics in Munich. I think that was the first course. I arrived in April of 1926.
Were the debates between Duane and. Compton over the reality of the Compton effect, which Duane was unable to detect, a subject of much discussion? Or did Compton’s being here make the Compton effect quite easy to accept?
My memory is that the Compton effect was accepted immediately, and that these criticisms by Duane and Clark — the box effect — this was discussed at length in the physics seminars, which I attended. The box effect — do you remember that? The box effect was that Duane and Clark reported that they got the Compton effect when they took the shielding box off the apparatus, and didn’t get it when they put it back on, or something like that. I suppose you know what the answer is in all of this.
No, I don’t.
Well, Clark, who’s retired now at the University of Illinois, just is a pretty poor scientist, and it shows up over and over again. Some of my papers are criticizing papers by Clark and Duane in those early days.
I didn’t find those.
Well, there are perhaps a couple of them. I have one from the Physical Society Proc., and here’s one [reading]: “About two years ago Clark and Duane announced the discovery of certain peaks [in the X-ray spectra reflected from crystals] and interpreted them as due to X-rays characteristic of elements in the crystals.” That’s Jour. Chem. Soc., 1925.
Yes, I did look at that paper on Clark and Duane in another connection.
Before that, I think, my third paper, “The Structure of uranyl nitrates hexahydrate,” Pauling and Dickinson [J. Amer. Chem. Soc., 146, 1924] here: “Clark reports” so and so. We found that everything that he said was wrong. It was very hard to find out how he got the results that he reported. Here: “The crystal structure of barite” J. Amer. Chem. Soc., , 1925 with Paul Emmett — he thought he ought to know a little crystal structure and he worked with me on this job. This — I guess this isn’t Clark — this is Sam Allison. Sam Allison had reported something, and he gave the size of the unit and then reported a reflection that had a spacing twice as large as would be allowed by his unit.
Exactly twice, yes. And he said that — you see he accepted the crystallographic unit, and then when he got the axial ratios — but in an orthorhombic crystal there’s no reason for the crystallographic axial ratios to be correct — you can multiply by a rational fraction. Clearly erroneous. I say of Sam Allison, “The author is aware of a difficulty here for he states that this result may be due to some accidental arrangement of atoms; however, it is not possible with arrangement of atoms in his unit to explain the observed reflections.” [Laughter]
You must have enjoyed that, somewhat.
This one with Bozorth: “If the results of this paper are accepted, the experimental peaks observed by Clark and Duane cannot have been produced by the reflection of characteristic caesium and iodine radiation.” And then there are a couple of later papers where I go after Clark. [Reading) “Unusual X-ray reflections on spectral photographs.” This is, I think, related — some reflections observed that can’t be accounted for in the usual way. I showed that they were due to diffraction from a powder that had been produced on the surface of the crystal by grinding. That is, where are crystallites that have a different orientation of the axes from the main single crystal that would presumably be —.
Was that Clark’s main trouble, that he was just sloppy?
That was his main trouble — just sloppy. I have photographs that I made of potassium iodide — I think I have another Physical Society paper in here, too, on potassium iodide. Clark used these photographs very much in his work with Duane. They were taken under the conditions that he used in his spectrometric work, the slit system built in the same way; arid you can see that instead of getting a reflection 310 into the ionization chamber, he was getting 311 from the layer lines above and below. This is probably the explanation of all of his peculiar results that he called reflection characteristic. Where you don’t have coherence, you know —. (That’s just) physics. I’m surprised at Duane. Duane was at Harvard. He had built that 100,000 volt battery to operate his X-ray tube in order to have constant potential. Whether he thermostatted the attic or not, I don’t know. At any rate Duane had done a lot of experimental work in the field of X-rays.
As I remember, Duane’s first criticism of Compton’s experiments was his own. It was before his collaboration with Clark.
It may well be. As I say, I was aware of this Compton-Duane controversy but probably at the time I was already so skeptical about anything that came because of these other papers that I gave it no weight. I can remember the discussions of the box effect and things of that sort.
What was the cause of box effect? Nobody knows?
What about de Broglie’s work. Was that discussed?
I’m not sure that I heard about his thesis before quantum mechanics came along. I don’t remember when I first learned about the wave length of the electron. One thing that I did that is related to this is that when I got back from Europe in 1927, I got a man, as post-doctoral fellow, to work for a year on an attempt to get proton diffraction patterns. This never was published. I thought, well, the proton has to have a wave length. This man did work for a year trying to get proton diffraction patterns from crystals, without success [pause] Robert (Dawson), I think Robert H., although I’m not sure, got his Ph.D. here. He was also an undergraduate. I had him work for a year as post-doctoral fellow, I think 1928-29, possibly ‘27-‘28, but along about that time, trying to get diffraction patterns of protons from crystals. And, you know, it may well be that he got some but that our standards were too high; we probably wanted very well-defined pictures such as you get with electrons. Then, some three or four years later, ’34 or ’35, after we had electron diffraction by gas molecules going well, I had a post-doctoral man –- a visiting professor. I asked the visiting professor here to try to get proton diffraction from gas molecules. I can’t remember his name. He was a principal collaborator of [Robt.] Hofstadter in the electron scattering from nuclei later on. He has a Scandinavian name that involves wine somehow. Vinyard; it’s almost like that. If I had Hofstadter’s collection of papers here, I could check it immediately, but I don’t. ‘Vinyard’ is almost right. Here again, he never was satisfied or I never was satisfied with the quality of the diffraction patterns that he got – protons from gas molecules. But here, of course, ever in 1927 there was no doubt in anyone’s mind, I think, that protons would have a wave length corresponding to their mass -– that the de Broglie wave length applied to protons, too. Now, where were we?
We were just finishing up the period before you went on your fellowships.
The Compton-Simon experiment and the box effect. Well, there was very keen interest here in all of these aspects of quantum physics.
Was there discussion of the Bohr-Kramers-Slater paper, the statistical energy conservation?
Yes, I remember attending the seminar at which this paper was presented.
Was there any enthusiasm for it?
I don’t think that there was. I wouldn’t say that there was enthusiasm for it. I don’t remember a single paper from the institute that could be said to be based on the virtual oscillators idea, and so on. I remember that it was called [pronounced] Bohr-Kramers-Slater because nobody had heard of Slater. He wasn’t recognized as an American. He had worked with Bridgman, you know, on crystals for his doctor’s degree.
So you thought it would be safer to pronounce all “a’s” long, then.
Well, then comes the question about the status of the Lewis-Langmuir theory here, and how you began to try to work in the dynamical aspects of the model.
Well, I accepted quantum theory, of course, at once.
As soon as you had heard of the Bohr atom? Had you made your first acquaintance with it through Sommerfeld’s book?
No, I think through Foote and Mohler, which may have been 1922-‘23, I’ve forgotten. I think Foote and Mohler came out in the summer of 1922 and that it was the basis of a course that I attended, taught mainly by Tolman during my first year here. And, as I mentioned also, we had a course on Lewis and Randall, Thermodynamics, that year. Well, then, when Sommerfeld was here, I presented in the physics seminar — which was only a small meeting held in a small library room over there — I presented my ideas about the nature of the chemical bond and showed some models. Let’s say this was 1924. [Goes away from the microphone.] I still have the models. Here is the water molecule [showing the model]: the two electrons, here are the two electrons holding the hydrogen atom, these are the two K electrons. They don’t need to be at that angle. I made these.
You’ve always made models!
Always, yes. [Chuckles) I think it’s rather interesting. Sommerfeld was interested. I had this little problem in that these models don’t have cubic symmetry, only tetragonal symmetry, and this bothered me. When I arrived in Munich in the spring of 1926 I found that Sommerfeld didn’t remember me; but then when I mentioned showing him these models, he remembered that.
Was the Lewis-Langmuir theory accepted; can one ever say it was accepted?
Oh, I think that it was accepted immediately by chemists, and that there was skepticism about the static electron concept, or aspects of it. I, for example, felt that there was a great deal to be said for what Lewis says is the Lewis [sic] theory. If you remember in his book —
In the ‘23 book?
Yes, where he says that in some quarters it’s called the Lewis-Langmuir theory but that in fact this is improper because there had never been any collaboration between them, and that Langmuir should get the complete credit for anything that he was —
That’s a most wonderful paragraph — “is entitled to the complete credit.” [Laughter]
As a matter of fact, he contributed quite a lot; and it wasn’t recognized generally. I even mentioned in the last edition of The Nature of the Chemical Bond that only some time after I had published some papers about the electro-neutrality principle did I happen to run across one of Langmuir’s early papers, 1919 or ‘20, in which he states the electro-neutrality principle. And I, no doubt, had read it at that time but just passed over it. We weren’t at the stage where this principle was of much significance or could be used very effectively. We had to have the ideas about partial ionic character of covalent bonds, you know, which I developed in about ‘33, ‘32, before it became possible to discuss electro-neutrality in a very significant way. Well, I think that chemists, generally, with an interest in structure, felt that there was a lot to what Lewis had said and what Langmuir had said; and it was just a question of finding how to make it compatible with what the physicists were saying. This is what I was trying to do in the talk that I’ve mentioned here and in my —
Yes, there was also a paper published in the Journal of the American Chemical Society.
On benzene. The structure of benzene [paper No. 1]. And. there was the paper that Hendricks and. I wrote on the trinitrides [J. Amer. Chem. Soc., 47, 1925); we make use of the Lewis structures. Those structures are —
But when you say the chemists accepted it, you have particular reference to the double electron bonds but not particularly to the cubical symmetry or the static nature of the bonds.
No, the principal point was that a pair of electrons held jointly by two atoms constitutes the covalent bond, or as Lewis says, the chemical bond. [Laughter] There were still problems, aspects of it that troubled people, but I think there was a feeling that this would all be worked out. I remember a seminar in physics at about this time on the Lewis static atom and the dynamic atom. And, you remember that along about ‘24, say, Fajans and Grimm published a paper on the structure of sodium chloride and other crystals that was just based on the static atom. Well, this was the sort of thing that didn’t appeal to me, that I wouldn’t have done.
Did you know about the spatial models of Lande and Born where the electrons move, but they move in peculiar ways so as to preserve some sort of polyhedral symmetry? They move in coupled elliptical paths and the whole thing pulsates.
I don’t think so. I may have known about these papers. I may have looked at these papers and just felt so little sympathy with it that I just forgot about it or ignored it. I don’t remember. I read Born’s papers, of course, the crystal papers, and his calculation of electrostatic energies of ions, that sort of thing. I have to say that I don’t remember papers by Born and Land on this subject.
It’s somewhat artificial because of intricately coupled elliptical motions.
Of course there was the paper on the hydrogen molecule in which the electrons moved with one another.
Yes. These were more elaborate for higher elements. What was thought of the Bohr scheme of building up the elements?
Well, my memory is that it was accepted, and that as soon as this Englishman introduced —
No, another fellow — introduced the change from four s and four p electrons to two s and six p electrons. It’s hyphenated, something like Mott-Smith.
There is a Mott—Smith, but I think Stoner is the one who is usually [mentioned].
There’s still another fellow, an Englishman, but I can’t remember anything else. I know Stoner. There was an English chemist, who was, I think, the first person to introduce the 2-6, and whether he also introduced 2-6-10, I don’t know.
Did the discovery of hafnium make a great impression, or not?
I don’t believe so. Hafnium and masurium — no, that’s rhenium and masurium.
The fact that hafnium was not a rare earth according to the Bohr theory?
I don’t believe so, but I’m not sure about that. I don’t remember that this was considered a very significant discovery.
Could one correctly evaluate your former impressions by saying that Sommerfeld did not give the impression when he was here that there were great problems and that Ehrenfest did? Or is that an overstatement?
I think this is right. Sommerfeld in discussing the old quantum theory in ‘24 gave the impression that here we had the solution, even though he didn’t say much about how the inner quantum number and outer quantum number were. I came away feeling, ‘This is wonderful.’ Ehrenfest was always talking, and very effectively, about the puzzling aspects of the old quantum theory.
So at Cal Tech then, even so late as ‘24, would it be correct to say that there was not the feeling that physics was in need of a dire and fundamental overhaul?
No, Ehrenfest had been here; and he did convert people. But there were other puzzles as I have mentioned with the dielectric constant. It was evident.
But that came after the revision of the quantum theory. Had you begun that before?
No, well it took — it came before, but I just was slow in publishing it.
Let’s see. It was received on the Sept. 10, 1926. “The Influence of a Magnetic Field on the Dielectric Constant of a Diatomic Dipole Gas” [Paper No. 4].
I think that — February, 1926, yes [Paper No. 3].
That was the first one, but this curious consequence of the old theory is in this later paper.
I think that I had worked it out already. Well, perhaps not. I was pretty slow in publishing this stuff.
But that’s extraordinary. It’s really a shame that you hadn’t run into that argument two years earlier.
Yes. Well, my memory is that I knew already before quantum mechanics was discovered that there was a difficulty in the dielectric constant. If you had spatial quantization of the axis of rotation in a magnetic field. And you see, until I carried out the detailed calculations I didn’t know how strong the magnetic field needed to be; but if you had spatial quantization in the magnetic field, then you should get a negative dielectric constant according to the old quantum theory. And experiments were carried out here, by [L. M.] Mott-Smith and somebody, I’ve forgotten whom, which showed that you don’t get this. I thought they might even be mentioned in the paper.
You do mention, them, yes.
I do mention them. Well, when you consider the time that it takes to get experiments carried out in some new field —
Did you undertake that paper specifically to investigate that point? Specifically to investigate the consequence — you had suspected that the consequence would lead to a negative result?
Yes, Mott-Smith and [C. R.] Daily. They had already published their experimental results; and you see, they did this work because I had made a prediction. I was just slow in publishing the stuff. Measurements were made by Mott-Smith and Daily and published in the Physical Review here before this paper had gone to press because — publication is given; theirs must have been several months earlier, I judge. And, the one thing that I didn’t know until I went to Munich was how strong the magnetic field would need to be according to the old quantum theory.
When did you actually go to Munich?
I arrived about the end of April, 1926.
So that was completed in Munich.
Yes, one of the first things I did there. That’s right. And, you see, I thought I could make a reasonably rough prediction about the strength of the magnetic field just by comparing the magnetic field energy of the magnetic dipole due to the rotation of charges in HCl — rotation of the electric dipole — with the energy involved in the dielectric constant, which is kT. And on the basis of this rough prediction Mott-Smith and Daily went ahead with their experimental work. You know, we weren’t in the habit — we were far enough away here from Europe so as not to be involved in this exciting course of development of quantum mechanics when the theoretical physicists communicated with each other by letter and kept one another informed as they were doing and rushed their results into print. It didn’t occur to me; I was used to waiting six months or a year before getting something published.
A whole generation would go by in those days.
Yes! You know, Sommerfeld said that I ought to talk to Pauli when we went to Debye’s magnetism [colloquium]; I didn’t go to it actually in ‘26, I hadn’t been invited; but then Sommerfeld sent me a telegram and said to come. This was along about June or July, 1926. When I got there he said I should speak to Pauli about this. I told Pauli what I had done, and that quantum mechanics would give this, and he said, “Not interesting.” [Laughter] Well, it wasn’t; quantum mechanics was accepted by that time, and that was that.
Did you have any trouble working out the calculations for that; that’s a non-trivial problem in the old theory.
That’s right; and I had trouble. I didn’t succeed in doing it in Pasadena. When I arrived in Munich, Sommerfeld — Sommerfeld was accustomed of course to providing problems to young people that came, and especially, I guess, Americans; I guess the caliber of some of them there wasn’t very high — and he suggested a problem to me. He said (Alexandroff) [sic., i.e., Max Abraham; see below] wrote a paper about the spinning electron around 1900; this is standard old electro-magnetic theory. With spinning electrons of different kinds he got different values of the g-factor.
Oh, yes, Max Abraham, who had been professor of physics at Berkeley.
When did he come to Berkeley?
Oh, 1895, say; and then he left.
Oh, he left; because he was at Gottingen.
Perhaps. He was also in Italy, wasn’t he, for a while as a professor; and then perhaps in Gottingen. Abraham, didn’t you know he had been professor at Berkeley?
No, I didn’t. Is it the same one?
Max Abraham. Yes, I’m pretty sure about this, and not (Alexandroff). [Laughter] So Abraham had got g = 5/3 for a shell electron and g = 2 for a uniform density electron.
Yea, he got — you get different numbers.
Well, Sommerfeld said perhaps I could work out something; I’ve forgotten just what the point was that I might do. Well, it didn’t appeal to me very much; at any rate I didn’t get anything out of it. I said to Sommerfeld, “What I would like to do would be to solve this problem of the motion of a diatomic gas in crossed fields.” I told him that I’d been having difficulties with it; I couldn’t evaluate the integrals. He looked at the integrals and said, “Well, why don’t you check up on these elliptic integrals?” He thought that I could transform them into elliptic integrals. And so after a while I did. You know, I’m not really a skillful mathematician.
It looks very impressive in that appendix you provide.
Yes, and I thank Sommerfeld. [Laughs] I didn’t say that he told me how to work out this integral, but that was his contribution. And of course from then on, he didn’t make any more suggestions to me; he just let me go my own way. Do you know the next thing that happened? Are you interested in this? I think there’s time. You might be interested in how I heard about the spinning electron.
This gives you an idea of what things were like. By this time, ‘25 the west wing of Norman Bridge [Laboratory of Physics] — well, we no longer see it — had been built; the east wing was there when I arrived. The west wing was built, and the physics seminars were being given in a room on the third floor that would hold about 50 people, close-packed. And I started over to the physics seminar one day — there were some other fellows around — and I met a fellow graduate student who was just bursting. He said, “Have you heard what had happened?” By the way his name is [C. F.] Richter. You see his name in the newspaper more often than anybody else — the Richter [seismological] scale.
Oh, oh, yes!
So here was Richter just so excited. He said, “Have you heard what has happened? A couple of Dutchmen, Goudsmit and Uhlenbeck, have discovered that the electron has a spin, is spinning on its axis.” Well, this was pretty interesting.
Did this come up? Was it discussed at the seminar?
I don’t remember. Gee, this was 39 years ago! I remember Richter, though, and how excited he was about this. And I was excited, too.
Why were you excited?
Well, this seemed wonderful, you know, just as wonderful as for the neutrino to be a little propeller.
It was the model aspect, where you saw the thing spinning, that appealed —.
That’s right. But of course I recognized immediately — and perhaps Richter even mentioned it; but whether he did or not, I knew very quickly that this accounted for that anomaly of the inner and the outer azimuthal quantum numbers — that it was electron spin effect that gave the fine structure.
Had you followed the argument of Pauli that required the four quantum numbers to be attributed to the electron because one would expect a relativistic effect if the tore spun in the higher elements?
I don’t think so; I don’t believe that I knew about that.
How did the Pauli exclusion principle effect people here?
Well, I can’t remember discussion of it at the time that it came out. I remember feeling satisfied with it, but that’s about all I can say.
This legislation for the periodic table satisfied you?
Yes. Up to that time I had felt that the sort of general argument that J. J. Thomson had given with his magnets floating on corks, you know — magnetized needles in corks — that this sort of argument might be a possible explanation. But it was hard to see how, why the numbers should remain constant throughout 2 to 92, or 3 is where it should start, 3 to 92 in the periodic system. Here is the sort of thing that I was thinking about in the early days — the quantum defects from penetrating orbits, where I evaluated polariz-abilities from the energy levels — the leucht-electron. All of these problems interested me, all sorts of things. I was thinking about nearly every theoretical problem that there was.
You mentioned that you heard about matrix mechanics essentially from the source when Born was here, I guess about the end of ‘25.
Yes, it was I think; I left here February ‘26, about.
I know from the remarks that you later make that you much preferred the Schrodinger approach. Was that reaction of yours typical? Did people have a much more positive response to Schrodinger’s methods than to the matrix mechanical methods?
Yes, I think so.
Was there enthusiasm at all for the matrix mechanics? Was it thought to be the solution when Born discussed it here?
Yes, I suppose so. I don’t know whether Schrodinger’s papers had been published yet when Born was here.
No, no, they hadn’t.
You know, I took full notes of Born’s lectures. But I just didn’t think that I was going to go ahead and do anything in this field.
It didn’t strike you as being the essential thing to master if you really wanted to pursue your own special area?
Weil, perhaps so; but it didn’t seem to me to be something that I should devote time to right then. It may be that ultimately I’d have to do it — I think this was my feeling. But as soon as Schrodinger’s stuff — wave mechanics — came out, that was ‘anschaulich’ enough to appeal to me.
Well, I think we’re about to go to Europe. Did you intend to go to Europe as soon as you had finished here? You did stay a year beyond the completion of your doctorate here.
I stayed about 7 months. I applied for and got a National Research Council Fellowship and I put down that I wanted to work in Berkeley. I was always interested in Berkeley, and G. N. Lewis. I had visited there a couple of times. Lloyd Jeffress was there in ‘25-‘26 as a graduate student in psychology. I saw G. N. Lewis in 1926, I think — ‘25 probably — briefly and asked if I could come up as a National Research Council Fellow. In the winter of ‘25 I met Frank (Adalot) who interviewed me, I judge; perhaps it wasn’t even an interview. I met him at dinner with Dr. Noyes; and I think Dr. Noyes had suggested that I ought to be a Guggenheim Fellow in the first batch. Well I hadn’t my doctorate yet, and I wasn’t in the first batch. I didn’t apply, you know. I suppose (Adalot) had said older people, somewhat older. Then after I got the National Research Fellowship, A. A. Noyes said, “You have quite a lot of work going on. Why don’t you stay here and finish up those crystal structure papers and whatever else you are doing arid then in the middle of the year you can go up to Berkeley. Stay here for a few months.” So I wrote and asked permission to stay in Pasadena for four or five months — four months or six months, perhaps — and I received it with a little complaint. They said National Research Fellowships have a requirement that you go to another institution. Then A. A. Noyes said, “Why don’t you apply for a Guggenheim Fellowship for the following year.” So I did apply for it for the following year.
And you never got to Berkeley.
And then he said, “You know, it’s so valuable to go to Europe; you ought to go to Europe right away. I’m sure that you’ll get the Guggenheim Fellowship; and the Institute will give you a $1000. And if you run out of money, I’ll advance some money to you.” He knew that I had difficulties and might run out of money. “I’ll advance some money for you. So you write to the National Research Council and resign your fellowship effective the 28th of February.”
Before you got the Guggenheim?
Yes, yes. So I did, and I got a letter back just lambasting me. You know, they said, “We have a certain amount of funds, and we give these funds for fellows and here you are turning back. You are not living through your fellowship year, and this is an improper thing for you to have done. Moreover, you were supposed to have gone to Berkeley; and you haven’t done it.” And after some years I realized Noyes was determined that I wouldn’t set foot on the Berkeley campus. G. N. Lewis came down. I’ve forgotten when it was that he was down here, but I saw him. It was quite rare for him to go anywhere. And years later he told me that he had come down to offer me a job, and A. A. Noyes forbad him to do so! [Laughter]
Why? Was there any reason other than his concern for your career that he didn’t want you to get involved with Berkeley?
Well, I feel that he was determined that I come back here and be a staff member here. He knew that I was interested in G. N. Lewis and the things he had done, and I think he was just afraid that I would be offered and accept a job at Berkeley.
I see; there wasn’t any particular animosity.
Well, no. Lewis had worked in the A. A. Noyes’ laboratory at M.I.T. for several years, and all of his early papers on thermodynamics were from that laboratory. They were quite different in temperament. There may have been a little animosity between Tolman and Noyes. Of course, they were together here for a number of years; and Tolman was of a different temperament from Noyes and from G. N. Lewis, too. I think this is what happened, that Noyes was just determined that I should be a staff member here. And, of course, he had formed, I judge, a very high opinion of me quite early. In 1931, when I received the American Chemical Society Prize, the Langmuir Award, the first time it was given, he said that I was the most able chemist that he had ever seen.
You were talking about Noyes guarding you from the ‘seductions’ of Berkeley.
Of course, I did then have a job at Berkeley for five years at the same time Oppenheimer was on part time appointment here and part time at Berkeley. For five years beginning in the spring of 1929 I, too, had an appointment. I was lecturer in physics and chemistry at Berkeley; and I alternated between the chemistry department and the physics department for between one and two and a half months each spring.
Oh, you stayed for a month at a time; you did live in Berkeley?
Well, I would live for a month or two months up there.
I think that Oppenheimer actually commuted, more or less, didn’t he?
Well, I think what he did usually was to be there for pretty much the whole of the academic year, which ended early, in April, and then be here for our third term. This is my memory of what he did during the period from about ‘28 to ‘40, about.
Was Lewis enthusiastic about your benzene paper [Paper No. 1]? Did he like that extension, or not?
I never found out. You see I went up in ‘29 and began lecturing on the nature of the chemical bond. I gave these lectures ‘29, and ‘31 and ‘33, say; and then in 1930 and ‘32 I talked about some aspect of quantum mechanics in the physics department there. Lewis and the other people there were quite enthusiastic about my ideas about the nature of the chemical bond. Lewis and I got along very well together; I liked being with him very much. We had wonderful arguments.
He was an extremely enthusiastic fellow, I understand, about whatever subject came up.
Did that first paper on the benzene ring attract much interest?
I don’t think so. There was a man here as professor of organic chemistry, Howard J. Lucas, who used it as the basis for some of his arguments. He had been one of the people in the pre-quantum mechanics days who had tried to introduce electron theory into chemistry and was pretty successful, in a rather simple way, of course. All of the arguments were pretty simple in those days. I, of course, didn’t pay much attention to my benzene paper either; it was just a phase as I was moving along.
But it’s quite interesting, for that reason. One of the things that interested me about it was your insistence, when you begin, that all physicists nowadays believe in these orbits, which is quite amusing, written at the end of ‘25.
Well, the difference between the quantum mechanical description and. the Bohr-Sommerfeld [sic.] description has never seemed to me to be a very great one, anyway.
Between the Schrodinger description.
The Schrodinger description, yes.
You say somewhere that the Schrodinger description is much better, much more like the chemist’s atom than the old theory. I think you wrote that in ‘27. What did you have particularly in mind?
Well, I suppose I had in mind the greater symmetry of the orbitals — of the orbits — where you do as I’ve done in these models [the models Pauling built]. That was something that bothered me. Perhaps that’s the most important aspect that I had in mind then. I don’t remember this benzene paper very well; there were quite a number of interesting comments in the paper, I agree — the discussion of the hydronium ion, which I call oxonium ion, isomorphism — actually there’s a good bit in this that is still valid.
And it’s quite interesting. Do you remember why there was such a long delay between the time it was submitted and the time it was published? I notice it because those papers bear both dates.
Yes, but I don’t think this was a long delay; I think this was just standard for the Journal of the American Chemical Society, September 14, 1925 to May 5, 1926.
Yes. That nowadays is admittedly very good, but in those times I think they turned those out a good deal faster in many cases.
Well, let’s see; here’s this one with Hendricks, “Stability of isosteric isomers,” October to March.
Yes, you see that went considerably faster.
That was sent in a month and a half later and published two months earlier. It may be that I had difficulty with the editor and with the referees; and this may not have been the paper that I wrote. I don’t remember. I remember that I was having difficulty with the editor of the Journal of the American Chemical Society getting theoretical papers published.
Regardless of the subject?
Regardless of the subject. And I’ve continued to be irritated by one fact; I wrote a paper in 1929, “The Principles Determining the Structure of Complex Ionic Crystals,” received September 5, 1928, published April 5, 1929. That’s not so much of a delay, but the paper is seventeen pages long, only about half as long as the one that I submitted. After this paper was published, within about six months, Bragg published a long paper, about 30 pages, that included the other half — it was essentially the other half. When I saw him in Manchester in 1930 he said to me — in fact it may not have been in Manchester in 1930 but rather in 1948 that he said to me –- “You know, I never have understood why you didn’t go ahead and make the applications of your nice paper describing those principles, the applications that I made in my paper.” Well, the answer is that I had made them and the editor wouldn’t publish them and I still, at the age of 28, had not gotten to the point of having enough self-confidence or independence to try to get the stuff published somewhere else, which I should have done.
Did the attitude change more favorably toward theoretical work after ‘29 or ‘30?
Yes, the Journal of the American Chemical Society began publishing theoretical papers and of course other journals came into existence at just about that time, the Journal of Chemical Physics in particular. Here I have material for a possible application to the International Education Board; this was before I applied for a Guggenheim Fellowship. This was written in the fall of 1925 I judge, because of the references, the papers that are given, several that were published in 1926 are mentioned. One is down to be published in December, 1925, but the page number isn’t given. Probably this is pretty much what I sent in to the Guggenheim Foundation, the suggested research. [reading] “Professor Sommerfeld has said, ‘To the future falls the task of working out a complete topology of the interior of the atom and beyond this a system of mathematical chemistry, that is, one which will tell us the exact position of the electrons in the atomic envelope and how this qualifies the atom to form molecules and to enter into chemical compounds.’ The subject of mathematical physics has been in existence for more than one hundred years. A system of mathematical chemistry that can achieve what we have just mentioned, that can shed light on the still very obscure conception of valency and can, at least in typical cases, predict the reactions that must occur is only on the point of being created. The work that I propose carrying on will, it is hoped, be one step in this direction.” And then the account of my Guggenheim Fellowship. (Moe) wrote, “the investigation of the topology of the interior of the atom.”
That was, so far as you can remember, a direct quote?
Yes, taken right out of this. This is a quote from Sommerfeld and it’s probably in Atombau and probably the English edition. We used the German the first year… And then there appeared the next year an English translation and we bad another course using the English translation.
You decided to go to Munich because of your earlier acquaintance or ‘brush’ with Sommerfeld?
Yes. Well, I wrote to both Sommerfeld and Bohr asking for permission to come as a Guggenheim fellow if I got the fellowship, and Sommerfeld answered the letter and Bohr didn’t. So I went to Munich.
Bohr didn’t answer?
Bohr didn’t answer, no.
That’s rather curious — I mean that Kramers didn’t answer!
Well, you know I can remember writing these letters; I wrote on an ordinary sheet of paper and longhand, just with a pen. It may be that Bohr or someone just thought ‘this is a letter we can ignore,’ I just don’t know. Then a year later I went to Copenhagen and I went because someone — some American or I don’t know just who it was — said, when I mentioned that, “Bohr just doesn’t answer letters very much but if you go up it will be all right.” So I just went up.
On the strength of that recommendation. Another itinerant American.
Yes. I didn’t stay very long — a month or six weeks.
Oh, you were there that long? But your main stay was in Munich.
Yes. You see, I was abroad nineteen months, my wife and I: one month traveling through Italy and about twelve months or perhaps only eleven in Munich and then a month or possibly a little longer in Copenhagen and then about three months in Zurich with Schrodinger.
What was the exciting thing in Munich when you got there? Bad the electron theory of metals started yet?
I think so. The exciting thing to me were the lectures Sommerfeld was giving on Schrodinger quantum mechanics and of course the seminars were devoted to it. I remember an American graduate student named (Cranston) giving a seminar talk on Schrodinger’s paper on the Stark effect and this was just terrible. I became very embarrassed and my wife did too because of the German students. (Cranston) showed that he just didn’t know what he was talking about, you know, and Sommerfeld said, “You’d better talk in English.” was having trouble with German too. But he couldn’t say it in English; I think he didn’t know what the ideas involved were, so be had to continue in German. He tried speaking in English, but the students began shuffling their feet and making noise in the way they sometimes do. I attended a meeting of the German Physical Society in which a member of the German Physical Society, an engineer who had an idea about Wirbelatome —
This was a little late!
Yes. — started to talk. He wasn’t on the program but just got up and started to talk and everybody there started talking to one another, shuffling their feet and banging books around. [laughter] Then we went down to the Hotel Union for dinner together and there was a U-shaped table at which the people sat and this fellow bad a little table for one put right in the middle of the U and was sitting there at his table! [laughter] This was part of his character.
That must have been somewhat hard on the gentleman.
Yes. So it was mainly quantum mechanics that interested people. There were two Americans, brothers, one of whom baa got out several books on electricity circuits and I don’t know what all; Ernst Guillemin is his name and he’s been a professor at MIT for many years. He’s very good. They both got their Ph.D.’s with Sommerfeld. Victor Guillemin was making, and got his doctorate for, a quantum mechanical calculation of the structure of the methane molecule considered to be a square pyramid, the carbon up here and the four hydrogens like this [demonstrates].
How did he possibly —?
I don’t know why he did this. I think at that time there was some difficulty in interpreting the band spectrum of methane on the tetrahedral model and the suggestion made by somebody, Dennison perhaps, that it was not tetrahedral but had a. square pyramidal structure. I think what he was doing was just to discuss the normal vibrations of a square pyramidal, not the quantum mechanics. This was before Heitler-London. This was just classical normal vibration theory.
I think J. J. Thomson did that calculation in 1906 or before, so far as I can remember.
Well, I don’t remember the details of Victor Guillemin’s thesis but it involved the square pyramidal structure of methane. Now, what else was going on? Unsold was there and Unsold at about that time developed Unsold’s theorem that completed or half-completed sub-shells have spherical symmetry.
Oh, yes. You mentioned that in the Royal Society paper.
Yes, this impressed me. This was important to me in the problems that I was interested in. Bethe came along about that time. He may have been there during the year ‘27; he may have been a first year graduate student there. I just have forgotten. I met him in Sommerfeld’s Institute.
Wentzel was still there, was he not?
Gregor Wentzel, yes, and a very interesting episode occurred shortly after I arrived. As I was reading the Zeitschrift fur Physik I saw a paper with the title, “Eine Schwierigkeit fur die Theorie des Kreiselelektrons,” and I thought, “Well now, here Wentzel has used a method of treating a many electron atom that seems to me to e just what I’m looking for.” — and of course it was the basis of my Royal Society paper [Paper No. 8] and most of the work that I did there –- “and the thing for me to do is to work through it and read it carefully.” So I did and as I read it of course I saw that there wasn’t any difficulty except that he had made a mistake. Do you know this?
Yes. The using of the improper principal quantum number.
No. Well, yes, I guess so. What he had done was to say, “I’ll carry out an expansion and retain terms only up to the square of the parameter that I’m using”; but actually he had omitted some of these terms. Well, he expanded some things and neglected terms of higher order than the first, than z/Z — but in fact he had neglected some of the term in z/Z, an error in this equation. Well, that’s what it was and just where those terms come in we’ll find as we go along.
Let’s see, I think you have a note here as I remember.
I have a note that Wentzel agrees. [Zs. f. Phys. 40, p. 348] Here we are — ‘Gleichung 3 of Wentzel is derived in the same way except that he assumed that n1 = n2 = n whereas I carried out an expansion to find —. This assumption is however not justified and leads to a considerable error.’ I have, I guess, the values for n1, n2, n3, and so on.
You have the recursion formula somewhere.
[Examining paper] — where we have these things in there so that n1 is equal to n times this expression [eq. 9 on p. 347) and if we expand that — well, perhaps we don’t even need to expand that. Oh, there —. Summation of zi/Z and here I’ve already neglected the higher powers, you see. Here is the expression, and if I expand that and neglect powers higher than the first in zi/Z I get this; and Wentzel had used only the first term.
Was this the error to which you refer in the beginning or was there also an error in the calculation, in the expansion?
No, that’s the error; but this is an error in the expansion.
Same thing, yes, fine.
But he didn’t bother to expand the ni.
Was Wentzel’s objection considered of any importance in Munich at the time?
Well, I suppose so. I think that it led to — there was some question as to what was wrong — although I suppose that many people would have said, as perhaps I would have too, ‘Well, this is a pretty complicated calculation and it may be that it isn’t a difficulty with the theory of the spinning electron but just a difficulty with Wentzel’s approximation.’
What is more, the question of whether you can even handle it that way I should think would immediately be asked.
Yes, that’s right. My memory is that I was interested even before I discovered that Wentzel had made an error; but as soon as I found that the agreement is really pretty good for s orbitals, not so good for p and d — that’s what these are — but for s orbitals, the more eccentric ones, it’s astonishingly good. As soon as I found that I thought, “Well now, I can just go ahead and make some calculations,” and that Royal Society paper involves a whole lot of —
Yes, of applications to —
I think this was really the start of quantum mechanics of polyelectronic atoms, that Royal Society paper of mine.
What about the somewhat different approach of the self-consistent field?
Well, that came along a little later.
How did they interact then?
I think the self-consistent field pretty veil took over.
That’s my impression.
You remember that in 1933 I wrote a paper with Jack Sherman on properties, on screening constants or scattering powers of atoms for electrons. That’s what it was — polyelectronic atoms. The results you can see from that paper — here they are –- “Screening Constants for Many Electron Atoms.” This discusses all properties of many electron atoms, that is, it’s a general way of discussing the properties where you use different screening constants for different properties and you can predict the values of the screening constants. Now here is a comparison: Hartree is a full line, Pauling-Sherman — this line that is low here and high here — exaggerates the shell effect, and Thomas-Fermi ignores the shell effect, so that the Hartree results, the self-consistent field results, fail in between the screening constant values arid the statistical Thomas-Fermi. And that’s true here too, you see, and here.
This is for what?
This is the f value, the scattering power for X-rays, which shows the screening of the nucleus by the extra-nuclear electrons. You see for a light atom the screening constant method is considerably better than the statistical atom; for lithium of course it’s almost —
Yes, and for sodium it practically coincides, the same as lithium.
When I prepared a list of scattering factors, f values of atoms, for the International Crystallographic Tables, I used the Hartree values when they had been calculated and I’ve forgotten what I did in cases where they hadn’t been calculated. I may have interpolated but I just don’t remember. After this correction of Wentzel’s paper, Sommerfeld I think felt that I could go ahead. [Laughter]
Did your correction come before the Royal Society paper?
Yes, I hadn’t worked out the Royal Society paper. That was the next thing I did. The screening constants in October ‘26 and the other one was January ‘27. Well, that difference — November, December, January — is the length of time it took me to do the work on that. Then the ions and ionic crystals is March, 1927. A couple of months.
Yes, once you got started you moved quite steadily ahead. Was Sommerfeld fairly approachable? I understand that once he’d picked a student he wanted to talk to, he would grab him at almost any time and proceed to talk.
Well, he was a rather formal fellow, in a sense, which probably frightened some people, but he was, I thought, very friendly and pleasant. After we had been there two or three months he lent us a piano which was brought up to our room; I think he even paid to have it brought to our roan. It was very nice of him. Re had two pianos and this one he lent to us; my wife played it.
Was it a fairly close group socially or not?
Weil, we went to Sommerfeld’s home occasionally by invitation and we associated with a few of the students rather closely. These two American boys lived in a room next door to ours in the apartment where we bad rented rooms, some (upper) rooms, and we saw a lot of them. Then we were good friends with Heitler and London at that time; well, we always have been, but they were there then. We celebrated Heitler’s doctor’s degree when he took his doctoral examination. We went with him and these two Americans and I don’t know whether London was along or not; and had champagne.
Did you have discussions on the chemical bond with them then?
Yes, I think so. I remember talking with a number of people about the explanation of chemical bonding in terms of the Burrau paper on the hydrogen molecule ion and the Pauli principle.
That’s how you got involved with the review article [Paper #10] I suppose.
Yes, but already in Munich I had seen it worked out and I didn’t think it was worth publishing. I had worked out the systematics of chemical bonding using the orbitals and the Pauli principle and assuming that an electron pair bond is just two electrons with opposed spin and a Burrau sort of two-center orbital. I can remember definitely these conversations with people. And Condon, you know, published a paper just about this time on the hydrogen molecule in which he got results as good as Heitler and London got later. Condon’s paper came first if I recall correctly. He didn’t evaluate the integral for inter-electronic repulsion but took a constant ratio to the Burrau energy using the helium atom where the value of inter-electronic repulsion is known; that is, he used an empirical method, essentially, to evaluate the integral. Burrau calculated as a function of inter-nuclear distance the energy of the hydrogen molecule ion.
By straight integration.
By straight integration, yes. This was numerical stuff; he didn’t have a — well, I’ve forgotten — he didn’t have an analytical function. Then Condon moved the nuclei together to get the helium atom where he had a value for the inter-electronic energy — this integral is known — and he assumed then that the correction would be the same fraction of the total interaction energy. Double the Burrau curve, correct by the amount necessary to get a fit when the nuclei —. This was pretty clever.
Yes, because that’s a Hund-like method where you look at the extreme cases.
Yes. I left that out of the first two editions of the Nature of the Chemical Bond sort of by accident and realized that I was doing —. Well, it wasn’t really by accident. The Nature of the Chemical Bond I thought of as a book on the electron pair or the covalent bond treatment rather than on the molecular orbital treatment, but then I realized that it was better to put in a discussion.
So the third edition of it has that?
The third edition starts out with Condon’s treatment. You see [showing book], Condon, Heitler and London.
1927, so they’re quite close.
They’re the same, yes. I think that in fact Condon’s paper was published first. I felt that there was just as much keenness of interest in the development of quantum mechanics and in science generally, just as much liveliness here in Pasadena as there was in any place in Europe. In fact I thought that it was better than any university that I was able to visit in that there were more lively seminars going on here. But of course at the same time Berkeley was going through an extraordinary period of lively development, too, especially in chemistry.
Were the important visitors who came here in the early ‘20’s usually fairly accessible to the students? Did they usually have students working with them? I know you worked with Debye and. others managed to collaborate a bit with important visitors.
Well, this place was a pretty small one. There were perhaps fifty graduate students all together in chemistry, physics, mathematics and a few other subjects at that time, and perhaps not so many as fifty in 1922 but around fifty by 1925. There was pretty good contact with visiting people who came through. Now my relation to Debye was a special one in that he had been brought here by A. A. Noyes because I had written that paper that I was talking to you about. Noyes wanted to find out his opinion of it, whether it was a real contribution or what, and I did write a paper with Debye even though he was here only for a couple of weeks. Now when Darwin came here I had good contact with him; he was here the whole year and I attended his courses. I remember talking with him; he was talking with me about the theory of space groups and asking why I didn’t carry on some sort of investigation that he thought would be interesting, a theoretical study. I don’t think he published any papers with any students while he was here. This is C. G. Darwin, the grandson, who became Sir Charles and had a distinguished career and died recently, a couple of years ago. I talked with Ehrenfest a number of times; I didn’t collaborate with him. I think his principal collaboration was with Professor Tolman. He was here for a couple of months I believe. Raman came through some years before he got the Nobel Prize. My wife and I invited Darwin to dinner in our house; I think that was my second year that Darwin was here, but I’m not absolutely sure. I would say, though, that there was good contact with these important outstanding people who came here even for short periods of time; they weren’t isolated from the students by any means.
What kind of an impression did Ehrenfest make on you?
Oh, I was very fond of him. I thought he had a very lively mind. My wife and I got veil acquainted with him. He was searching for the answers, all right, the answers to these various quantum theory paradoxes. I thought that he was a keen fellow. Later I got pretty well acquainted with his daughter. His son, of course, was mentally deficient and ultimately Ehrenfest, I judge, killed his son and himself. He committed suicide and killed his mentally deficient son, whom I never saw.
No, he was in an institution.
But I think Ehrenfest must have got him out.
I think the institution was in Germany and I think that with the Nazi’s coming to power his son was forced to leave. I would be very much interested to have your comments on the growth of the notion of uncertainty and complementarity, especially since you express yourself in several places in favor of Schrodinger’s interpretation of the wave function. This is before uncertainty and complementarity were well defined concepts, but at the time you speak quite highly in favor of a concrete representation of the wave function as charge density.
Well, first I tend not to be interested in the more abstruse aspects of quantum mechanics. I take a sort of Bridgmanian attitude toward them. Bridgman with his ideas about operational significance of everything would say that a question that does not have operational significance, that does not lead to an experiment of some sort or an observation, isn’t significant. I never have been bothered by the detailed or penetrating discussions about interpretation of quantum mechanics. In my (Messenger) lectures for example I discussed the matter of free will or determinism. There has been the contention that the uncertainty principle means that we are able to accept the concept of free will whereas, according to classical mechanics, free will was ruled out, in that the world was determined. If we knew the positions and momenta, the velocities, of all of the particles in the universe then we could predict the entire future history of the universe. My answer to this is that in fact the existence of the uncertainty principle does not affect the validity of this statement at all in any practical sense. Even if this were a classical world it would be impossible for us to determine the positions and momenta of all the particles of the universe by experiment. But even if we did know them, how would we carry out the computations? We can’t even discuss in detail a system involving, say, 1020 particles or 1010, so that I think it is meaningless to argue about determination versus free will, quite independent of the uncertainty principle.
Even if it were possible in principle to say free will through the uncertainty concept, I don’t see what satisfaction it would give the holders of the free will point of view.
No. Now about the interpretation of the Schrodinger function, the square of the Schrodinger function as the electron density function. This of course is a special case of quantum mechanics where the energy is determined exactly, the simple case, and I don’t know even now that there is any contradiction between this interpretation for the special case and the generally accepted general interpretation about probabilities or about transformation theory.
Well, one has a different representation of course and once one gets to more than one electron then one has to deal in a coordinate space which of course makes the physical situation obscure.
Sure, although there have been some people working on quantum mechanics of atoms or molecules in which one deals only with the total electron density function.
Yes, and of course Schrodinger had a way in which he tried to put a many electron atom in coordinate [real] space by integrating over — Perhaps you recall his fairly elaborate treatment which so far as I know didn’t meet with much sympathy in Europe.
I don’t remember. That would be integrating over all of the electrons except one. — If you take the general function and integrate over all electrons except one, then you will get an electron distribution that includes all of what are ordinarily called one-electron functions. I haven’t followed this aspect of quantum mechanics enough: to have a firm knowledge.
Do you recall discussions at Munich on the subject? Was it something of much interest? Was the uncertainty principle, for example, discussed?
I don’t think that it was discussed very much. My memory —, and of course my memory has probably been determined in considerable part by my interests both then and since then —, my memory is that everyone was so excited about the possibilities of solving problems, answering questions, the mechanism provided by the new quantum mechanics, that there was little discussion of these details of interpretation. And of course Sommerfeld’s nature, as you can see, is along these lines whereas Bohr’s was different.
Yes, it would have been a rather typical Munich response. What about the situation then in Zurich when you visited?
In Zurich then when I went there I saw Schrodinger. I may have attended a few of his lectures and some of Debye’s lectures — I guess that’s right that Debye was there — and perhaps more of Debye’s than of Schrodinger’s. I don’t think I ever discussed my work with Schrodinger and I don’t think that Heitler and London discussed theirs very much although I am not sure.
Yes, I understand that they did not.
I think that we all went for a walk with Schrodinger once or twice. I worked in the room in which my wife and I lived.
You had no official connection, then, in Zurich?
I don’t think that I registered anywhere there. Sommerfeld was disturbed, after I had been in Munich for a year and had attended all of his lectures — practically every lecture that he gave during this period — and his seminars, to find that I had no official connection with the university. He thought that I had been admitted some way, had gone around and registered and paid fees and so on, but it didn’t occur to me to do anything and I didn’t. It may be that I just avoided doing anything when I got to Zurich as a postdoctoral fellow. So I worked away in my roan most of the day and then perhaps went to a seminar; my memory is that I didn’t attend lectures very much.
And you don’t recall that the interpretation question was much discussed?
No, I don’t recall that this was much discussed. It may have been without my being present, or even if I was present, without my paying much attention to it.
And what of Copenhagen? There there should have been discussion of the interpretation.
I can’t remember that there was a single seminar in Bohr’s institute during the time that I was there and I don’t remember any discussion about the interpretation of quantum mechanics. I remember how I put in my time; when I got there I met Goudsmit and talked with him about various things. Goudsmit was interested in hyperfine structure of spectral lines due to nuclear spin and I think it was Pauli who had suggested that the spin of the nucleus might be responsible for the observed hyperfine structures of line spectra. Goudsmit said that perhaps I would be interested in helping him in explaining the hyperfine structures and so I worked on the theory of hyperfine structure while I was there. He and I, as it turned out, never published a paper on this subject but when I wrote — we wrote it together but in a complicated way — the book, The Structure of Line Spectra, one of the chapters contained the material that I had worked on while I was there. I think I probably did some work on chemical bonding, too, while in Copenhagen, but I didn’t get any help from anybody.
No interest, no. Bohr asked Goudsmit and me to come in to see him, perhaps a week after I arrived, and we went into a seminar room, just the three of us. Goudsmit and I told him what we were working on and he said, “Very well.”
And that was the end of that?
And that was the end of that. I had seen more of Bohr while I was her, actually, during his visits — or perhaps there was only one before ‘26 when I left here — than I did in Copenhagen.
He and Goudsmit had been working on the design of models, I think, in the old style but using spin in order to account for the hydrogen molecule, I think, or maybe the helium atom. Did you discuss any of those things?
I don’t think so. I don’t think that I discussed that with Goudsmit. One thing that I think we did discuss at this time was taking the square root of j times j plus one, or square root of l times l plus one, s times s plus one, as the magnitude of the angular momenta rather than just j times h over two pi. I was especially struck —. Well, you know my interests in susceptibilities —. I had already been especially struck by the fact that the Debye equation for the dielectric constant and the Langevin equation for paramagnetism are valid in quantum mechanics and that cos2θ averages one third in quantum mechanics for all states if one interprets the total angular momentum vector as a square root of j times j plus one. I emphasized this strongly in the book that we then wrote on the structure of line spectra and I think that perhaps I was the strongest exponent of this interpretation. Of course in three dimensional space — field free — the square of the angular momentum is a good quantum number, a good dynamical quantity with fixed value, and j times j plus one is the quantity that comes in; in fact you can say that the square root or any power of total angular momentum is good, and you have to put j times j plus one in, so it’s only natural. The component of course is j. Now this didn’t seem to me to have any philosophical significance; it has perhaps a correspondence principle significance in that the correspondence principle is valid down to very — valid even when b is large for this’ particular thing if you make this interpretation.
In connection with this philosophical discussion of the free will and so on, did you ever hear Bohr discussing the problem of the freedom of the will from the standpoint of complementarity?
No, I don’t think I ever did. I read his book on the subject and I find myself completely uninterested in the arguments.
Did anybody pay any attention to Pierre Weiss anymore concerning magnetic moments?
Weil, this was a part of my early knowledge in the field of magnetism but I think that already as soon as Bohr’s theory was developed and the Lande g factor was discovered, the Weiss magneton was just discarded. There was an interesting problem as to why it should be so close to one fifth of the Bohr magneton. There’s a possibility that this might have turned up in the interpretation of ferromagnetic saturation moments; with paramagnetism it is impossible that it could have been meaningful. With the ferromagnetic saturation moments where the observed values come close to being multiples of the Bohr magneton then you might think that the exceptional cases happened to be a fifth or two fifths or three fifths or four fifths and that this might have led Weiss to adopt the value he did. My own feeling is that it’s just accident.
That’s what it seems to be.
Yes, that he got a value that was pretty close to a fifth of a Bohr magneton. Now I attended in 1926 in Zurich the conference on magnetism that Debye had called and I heard Langevin speak there, the first time that I ever heard him speak, very beautifully; and I participated to some extent in the discussion. Cabrera was there talking about magnetic moments of rare earth ions. The only memories that I have of this meeting are those that relate to pretty straightforward interpretations, theoretical studies, and I have no memories of philosophical questions or interpretations of quantum mechanics going beyond the conventional, straightforward ones.
Well, there is the question of whether they were straightforward since one had a considerable debate on the issue between Bohr and Einstein, and Bohr and Schrodinger.
Yes, but as I say, I just couldn’t get interested.
It didn’t bother you at all?
No. The question in my mind was, ‘Is quantum mechanics, wave mechanics, for example, sufficiently close to being correct so that if we solve the equation we’ll get the right answers in relation to the properties of atoms and molecules?’ — not even going beyond that to the nucleus, but just atoms and molecules.
How did you arrange for your visits? You told me about how you happened to go to Copenhagen. What about Zurich? I told you, I think, that I found the letter you wrote to Schrodinger.
As I say, I wrote to Bohr and Sommerfeld, I know. Well, I got out some correspondence; I saw that I had a folder labeled 1927 and you see [showing material in the folder] that this is hyperfine structure stuff that I was working on.
[Reading] “First of all, many thanks for your correction of my English paper and for the Saturday Evening Post.” I translated some stuff of his [Goudsmit’s], I’ve forgotten what it was, relating to hieroglyphics.
Oh, yea. I was interested. You translated that, did you?
Yes, I probably made an English translation of that, but you see I translated his whole dissertation from Dutch to English.
Oh, I hadn’t known that it was originally written in Dutch.
It was published in Dutch.
Oh yes, of course, you’re right; I read it in Dutch.
I had learned enough Dutch — you know I bad always had an interest in languages although I am not a skillful linguist — but I learned enough Dutch to translate this dissertation and it constitutes, with some changes, the first three chapters of our book, The Structure of Line Spectra. This [material in the 1927 folder] seems to be largely correspondence with Goudsmit relative to that book, and with other people too.
Relative to the book? Oh, it runs through ‘28 and ‘29.
This first letter may not; I don’t know that we had decided to write a book at that time. I’ve forgotten. This may have been on whether we would publish something about hyperfine structure.
When did you decide to write the book with Goudsmit?
Well, when I finished translating the dissertation it seemed to me that it was unsatisfactory as a presentation of structure of line spectra. I think that perhaps it wasn’t the first three chapters but was some others; I may have written the first three chapters as the introduction and then brought in these three chapters about the vector model and then added three more. I think there are about nine chapters in that book. I don’t know, I no longer remember when I decided to do that. Goudsmit and I were never together, I think, during the period when this book was written. He would write a draft of some material that he thought ought to go in the book and then using that as a basis I wrote the COrre8pOflding sections of the book.
I see, so you really put it together.
I wrote the whole book but a large part of the material, perhaps the material in six chapters of the nine, came either from his dissertation or from drafts that he sent to me, rough drafts of spectroscopic material that he sent to me.
Did he discuss with you his big step of coming to the states to teach at all during the time he was making that decision?
I think so. Yes, I think he did and Uhlenbeck did too.
You were able to convince them that it wasn’t the end of the earth? [Addressing his two biographers also present]
We’re getting all of this down so you can have this.
May I ask something on the side perhaps? I just wonder — you speak about working on line spectrum theory and I don’t have much of a picture of what working means, to what extent it’s thinking and talking, to what extent it’s working with building models or in the laboratory testing things.
Oh, yes. Well, this would be purely mathematical, let’s say; more than that, theoretical. It means working with pencil and paper, and I have, not here but at home, perhaps this much — sheets of paper several inches thick — which are calculations that I made in theoretical physics during the ‘20’s.
Before even the European trip?
Some of them before, yes. I don’t have them here but I have all of these notes. Some of it has no significance, of course, and some of it turned into something worthwhile. You were asking why there was this long gap from 1928 when I wrote my first paper on quantum mechanics of the chemical bond in the Proceedings of the Royal Society, and 1931 when I wrote the first significant paper. Well, there was this gap because I was having so much trouble getting a result that was in simple enough form to be valuable to chemists and to have more significance than numbers that you would get out of a computer nowadays. In this 1928 paper that I wrote –- here — I had written a long review article, “The Shared Electron” [Paper No. 9] —. Well, I wrote a long review article, “The Application of Quantum Mechanics to the Structure of the Hydrogen Molecule and the Hydrogen Molecule Ion and Several Related Problems” [Paper No. 10] in which I gave for the first time that it was given, in fact, — I think this is right — what would be the Heitler-London treatment of the hydrogen molecule ion, just the simple jumping back and forth. For some reason this hadn’t appeared in the literature, and then this was mainly just a review article. Then April 1928, essentially simultaneously, I said that application of quantum mechanics enabled us to see that in a molecule such as methane where there are the four hydrogen atoms we do not need to describe the electrons of carbon as occupying an s orbital and three p orbitals, but they can be hybridized to get the tetrahedral orbitals. It doesn’t mention hybridization, but it is this paper in which this statement was made for the first time. I can do this hybridization and get some complicated expressions, you see, but having done that I didn’t feel satisfied, so it wasn’t until about December 1930 that I made the step of assigning the same radial function to the s orbital and the p orbital essentially.
I was going to ask you about that!
Let’s just look at the angular dependence and see how that comes out.
It shattered the physicists, didn’t it, to see you do that.
Yes, and of course it’s really a remarkably good approximation, a zeroth approximation or perhaps even first approximation; it works a lot better than further approximations.
Well it certainly makes the angular dependence easy to discuss.
Yes. Well then I felt pleased, you see, and published this second paper in 1931. Then I went on to publish a number of others quite quickly on various aspects of chemical bond theory, but all during this time I tried essentially to work out hybridization of bond orbitals in a simple enough way so that I could get somewhere in a finite length of time in making calculations.
I see. How was that presentation received? Do you know how the physicists reacted to it?
Well, I don’t know. I think Slater hasn’t been especially unfriendly to it. Mulliken and perhaps Slater began saying that to assume that the overlap integrals are the same for an s function and a p function is a very poor assumption; they really are much different. Moreover this quantity that I call the bond strength that involves just the angular dependency is by no means proportional to the overlap integral and this is consequently a poor approximation. They’ve been saying this for years. They started out right away saying that this wasn’t much good and they continue to say it.
But it didn’t particularly disturb you?
No. I published a paper with Jack Sherman on the calculation of some of these overlap integrals with a simplification — I don’t know that it’s in these volumes. It’s in The Nature of the chemical Bond, the results are — with a simplification of some sort; it’s like taking Slater functions, I don’t know what it was, but actually evaluating the overlap integrals. Our conclusion was that the bond strength function giving angular dependence alone, is really pretty good, not perfect but pretty good.
At least it can be done. Did you discuss these matters in Zurich with Heitler and London? I guess they had just about arrived at their theory.
Yes, I think they published their theory just before I arrived in Zurich. I’m not sure about that. I discussed it with them a little. I think they were working then on the extension of the theory to many electron atoms and their group theory discussion of chemical bondings, but they didn’t invite me to participate in the work. In fact I spent most of my time in Zurich attempting to treat the interaction of two helium atoms.
Well, they did that in their second paper.
Yes, but you see even in their first paper they used an approximation to one integral. Sugiura then evaluated it, and in their discussion of two helium atoms they again used approximations.
So you wanted to do more than that.
I was trying to evaluate these integrals rigorously and this was before Sugiura had evaluated them so that much of my time in Zurich I really wasted in an effort to get good approximate values to sane integrals that come in the Heitler-London treatment of relatively simple molecular systems.
You had no doubt that that was the correct general approach?
Well, no. Well, I thought there was a possibility of doing something better but I didn’t know what it was that needed to be done. Here I think I had the feeling that if I worked in this field I probably would find something, make some discovery, and that the probability was high enough to justify my working in the field. Of course, it led to hybridization and all of this stuff.
Oh, yes, you couldn’t have asked for more out of it.
Yes, and I put a lot of things in the 1931 paper that continue to be rediscovered I judge. The concentration of electrons along the bond axis, you might say, would mean the contribution of d and f functions in the methane molecule, say, to the bond orbitals of carbon; it means that they aren’t just s, p hybrids but have d and f contributions too. In this paper is a statement about this in a little different nomenclature [showing a paper].
The group theoretical methods, though, didn’t appeal to you?
Not very much. I studied group theory; in fact I think I had done some group theory already earlier. [Looks through papers] Here I have ‘Groups, Dr. Bateman’; let’s see what that is — ‘the group, of displacements.’ Now this was probably about 1925 I have Bateman’s notes on group theory and here’s something of mine — I don’t know what that is. Now these notes aren’t dated and mine aren’t dated. Bateman did so much; you know the Bateman project and the various volumes that have been got out from his unpublished materials. You know there was several hundred thousand dollars given to the Institute after Bateman’s death, by the Ford Foundation, I think, and a team of mathematicians worked for years on Bateman’s notes and got out several published volumes of which I have some. He had two houses across the street here that are still there. He had one house and he started working and when one room got full of his notes he moved into another one and when this room got full he moved into another one. And then he moved into the next house! [Laughter]
Did the exchange energy interpretation of chemical bonding experience any difficulty in acceptance? It wouldn’t seem to be something that a chemist would necessarily be overjoyed about. Did you experience any troubles?
I didn’t experience any troubles. I accepted it. The Ritz theorem of minimization of energy of solutions of characteristic value equations —
This principle I think I just accepted as something about mathematics, you know, and then having that, the variation method followed.
Well, I meant more the picture that one was presented with, with these electrons hopping about and so forth.
I think I accepted exchange energy just as a part of Nature that we hadn’t recognized before. I used the variation principle or Ritz principle as the starting point that if you have one structure for the hydrogen molecule and then another structure for the hydrogen molecule or — it goes back to Heisenberg — you have one structure for the 1S, 2S state of helium, with wave functions. The sum of these functions, or the difference would represent two other structures and these would be states, one of which would be more stable and the other less stable, than the constituent structures. This I just accepted very quickly and soon began thinking along these lines. Then it wasn’t until later on that I recognized — someone else pointed out — that the whole thing depends upon a shifting of the electron distribution such that you get the electrons concentrated in the region where there is greater interaction with the nuclei, the region between the two nuclei. I didn’t find any difficulty in accepting these new ideas.
What about your chemical colleagues?
Well, they had difficulty with quantum mechanics as a whole, many of them. I think the young ones had no trouble but the older ones did. Fajans is an example, Kasimir Fajans. Here he was, Professor of Physical Chemistry in Munich, and one felt that he was one of the leading physical chemists in the world. When I was there in 1926 and ‘27 he was already so busy he said that he had material for twenty papers just waiting for him to get time to write it up, work that his students had done on the optical properties of substances, measuring index of refraction and calculating more refraction values, polarizability — he was interested in polarizability in connection with the idea that everything was built of ions and the ions were polarized. Well, he was just so busy that, as he said to me a few years ago, he never got time to learn quantum mechanics. He was relatively young, perhaps 40, when I was in Munich, but he was old enough and important enough, and as a chemist, even a physical chemist with a European background rather than an American background, he was so lacking in his background that it was impossible for him ever to learn and to understand quantum mechanics. This was his situation. Now this of course has continued for quite awhile with chemists in Europe, that they did not study physics and mathematics; but here, at Berkeley and at Pasadena, the chemists, the physical chemists, were learning as much physics and mathematics as the physicists did and they were able to take advantage of this opportunity in the way that European chemists were not.
What about the older chemists here?
The older chemists here I suppose varied; some of them were broadminded. Well, Tolman is an example; he was trained as a chemist but he branched out into physics by himself pretty largely. His training was as a chemist, his PhD was in chemistry. G. N. Lewis was interested in the theory of relativity as soon as it came out; he wasn’t a skilled mathematician, but —
He was an extremely remarkable fellow, yes.
Yes, he was a remarkable fellow, interested in everything, and be was interested in quantum mechanics although be never published a paper or made any contribution in this field. I think that’s right; I don’t remember that he did. And what about other older physical chemists in the United States? I think that probably many of them were better prepared to accept quantum mechanics than the physical chemists of Europe were.
That is to say because they bad more mathematical knowledge?
Because they had more knowledge of mathematics, yes. The difference in the educational system between the United States and Europe even then was that here graduate students were still attending lectures and taking courses, whereas in Europe they settled down to research in a very narrow field, immediately on getting into what we would call graduate school, to work on the doctorate. Well, in Germany of course it was a little different.
One learned a bit more as an undergraduate.
They learned more in the gymnasium before going to the university and then it was customary to spend a couple of years, four semesters, going from university to university, taking courses before settling down then to doing the thesis and taking the examination. So the German system was a little different from the British, say. In 1948 when I was in Oxford as Eastman Professor a student who came to work for a ‘D. Phil.’ which is the degree they gave then, would just start doing research in a narrow, specialized field and that was that. Up until about this time that was the situation but then at Cambridge they introduced the idea that there were certain courses that students should take before they did research.
Did the inability of the European chemist, or some European chemists, to appreciate the quantum mechanical interpretation result in some antagonism towards the sort of work attempting to explain chemical phenomena?
Well, I think it probably did, and also resulted in the failure or inability of European chemists to contribute very much to the development of modern physical chemistry and structural chemistry. The United States has been the leader in this field and in Europe the people who have become outstanding have been for the most part physicists. You take [C.A.] Coulson, a mathematician really, you see.
Well, Heitler and London; Hund.
Heitler and London were both physicists. And Hund, yes. There are others, the younger ones —. I don’t think they have been chemists; they may become professors of theoretical chemistry but they have started out as physicists and are essentially physicists, not chemists.
Were you ever tempted to physics yourself during these years that you flirted with it so intimately?
When I was in Europe, I think in Zurich, I received a letter from A. A. Noyes saying that he was writing to offer me an appointment as ‘Assistant Professor of Theoretical Chemistry and Mathematical Physics,’ and I accepted it, but by the time that I got here it had been changed to ‘Assistant Professor of Theoretical Chemistry.’ The physics had been dropped although Tolman was appointed jointly in chemistry and physics. He was Professor of Physical Chemistry and Mathematical Physics. By the way, my appointment that Dr. Noyes wrote to me was to be theoretical chemistry and mathematical physics. I don’t know what happened with the physics, whether Millikan objected to my having a joint appointment or whether Noyes decided —. As I mentioned to you this morning, he was preventing me from being given an appointment at Berkeley, preventing me from going to Berkeley, and he may have decided that he didn’t want me to be associated with the physics department in this way, that perhaps I would shift.
That would be the loosening wedge!
Yes. I didn’t care; I was just as pleased to be Assistant Professor of Theoretical Chemistry but pretty soon, when I became Professor in 1931, I said I wanted to have the title of Professor of Chemistry, not theoretical chemistry, just Professor of Chemistry, and not physical chemistry either. Dr. Noyes at one time, along about 1930 or ‘31, asked if I wouldn’t be interested in becoming an organic chemist; I made contributions of course to theory of organic chemistry and this may have been around ‘32 or ‘33 that he suggested that. The theory of resonance was a big inspiration, a big help to organic chemistry, perhaps even more than to inorganic chemistry. In 1929 I was offered a professorship of physical chemistry at Harvard; actually I was offered the post after Theodore W. Richards died. I was offered the post of associate professor of physical chemistry and I went back for a week to Cambridge and stayed with Conant in his house. He was ahead of the chemistry department. When I told him that I would not accept it he asked if I would accept a professorship and be professor of physical chemistry and I said no, I would not accept that.
Had you nearly made up your mind before you’d gone back?
I was in Berkeley and I received the letter; the job was offered to G. N. Lewis and he turned it down; I think it was offered to Tolman and he turned it down, and then it was offered to me. I believe this is the sequence, but it was an associate professorship that was offered to me and I was invited to come to visit them for a week, so I went back to Cambridge and stayed there for a week and talked with various people about it.
You were seriously tempted then, at least seriously enough to go back.
Well, I thought that I shouldn’t just say no without examining the situation. I decided that I would be better off here for various reasons so I said no and then as I say, I said I wouldn’t even accept a professorship.
Were there particularly unattractive reasons about chemistry at Harvard?
Well, the department of chemistry seemed to me to be rather uncooperative in that the different professors ran their own little groups. I learned that they had some money for support of their research — it wasn’t clear how much I would have, I don’t remember that they told me exactly what support I would get — and instead of going to the stockroom to buy apparatus they went out to a shop somewhere in Cambridge to buy apparatus because the prices were so high in the stockroom. The fellowships, the support of fellows, was not much different from what it had been seven years before when I felt that it would be impossible for me to get a PhD at Harvard and had decided not to accept the assistant instructorship that they offered me. I just thought that I wouldn’t feel at home there, aside from its being the East Coast rather than the West Coast.
Any one of those reasons would be quite good!
I looked about for a place to live on the salary that they offered me — I don’t remember what the salary was — and one of the younger men, an instructor or an assistant professor, invited me to his home. I just didn’t want to live there in Cambridge.
Could we speak briefly about the developments of physics during the time between ‘27 and, say, ‘31, the time of the Dirac equation, the discovery of the positron and the beginning of quantum electrodynamics and the gen era trend of physicists into nuclear physics and so on? In particular, was the Dirac theory a subject of much discussion here that you can recall?
I don’t remember that it was. I met Dirac in Gottingen and I don’t remember whether this was 1926 or 1927 and I didn’t have any discussion with him. I met Oppenheimer there too for the first time. I bought Dirac’s book and learned enough to satisfy me; that is, it seemed to me that there was no incompatibility between transformation theory and quantum mechanics as I had been teaching it and applying it, and that there were elements of usefulness in transformation theory. And in fact, of course, I wrote a paper with Podolsky that made use of it in a simple sense. I was interested in the question of what the momentum wave functions were, the momentum distribution, and I tried to solve the problem. In Dirac’s transformation theory the wave function in coordinate space is the transformation function, and so on. For momentum space we might have a similar function given the symbol [demonstrates] — and so on — and we can get that in this way, by carrying out this integration. This wasn’t known for the states of the hydrogen atom although Weyl in his 1928 paper said that these functions were in his dissertation in 1908. We couldn’t find it; I couldn’t. I tried to evaluate this integral and couldn’t do it. It’s a long time now, 1930, but I never knew what Weyl was thinking of when he made that statement; perhaps his memory just failed.
Did you correspond with him on that point?
No. I knew him; I had met Weyl in Zurich but for some reason we didn’t write. Well, I told Podolsky that I was working on this problem and couldn’t evaluate the integral and he said that he would try it; in a few days be managed to do it • He found the papers by (Bauer and Gegenbauer).
That’s quite a team.
Yes. (If it isn’t) it’s just by (Gegenbauer) but I think we managed to get a reference to (Bauer) in. No, there’s no reference — just one to (Gegenbauer), these (Gegenbauer) polynomials. This integral is a very useful one; we used the same general integral later on in those calculations of X-ray scattering functions in atoms. Then my book disappeared, my Dirac, and for a long time I didn’t have it and I don’t know that I have it yet. What happened was that there was a student, an undergraduate student, here, who was a sort of nuisance because he was always into trouble and I had known him while he was still in high school and had known his mother too. He was supposed to take a course on introduction to theoretical physics that Houston, Bill Houston, was giving. Houston came to me and said that this fellow wasn’t coming to the course and that he was going to have trouble with him sooner or later; that in fact he knew enough theoretical physics so that it would be all right if he substituted something else for it. For some reason, and it’s not clear to me why, he would like to do some work under my direction and Houston asked whether I would supervise this fellow and give him credit that would be equivalent to the required course. So I said I would and he came around. I gave him The Structure of Line Spectra and some years later he wrote a paper on evaluation of polarizabilities for non-penetrating orbits much like that talk that I had given earlier. This was in The Structure of Line Spectra, how to calculate these quantum defects from polarizabilities. He did all of that in a couple of weeks; that is, he read The Structure of Line Spectra. I gave him Dirac’s book on quantum mechanics then and supervised him while he worked through it and then he didn’t ever give the book back to me.
He didn’t ever finish working through it!
His name is Shockley, William Shockley.
A book well spent.
Yes. He was always a very lively fellow.
What of the positron? Do you recall the local steps leading up to that?
I knew Carl Anderson well; he was Junior Travel Prize winner. There were two boys who won the Junior Travel Prize in 1925 and my wife and I saw them in Rome on Easter of 1926; they were there already. He was a junior that year, ‘25-‘26, and he and (Fred Ewing) had six months abroad. Then I knew him as a graduate student when he was here; this study of cosmic rays with the Wilson Cloud Chamber in a magnetic field was something I suppose Millikan had suggested to him and. he bad got the apparatus and was working away. The only thing that I remember about the discovery of the positron that might have some special interest is that E. T. Bell, who is now dead, told me just about the time that Carl Anderson published this paper that Carl bad mentioned to him that he had a pair of tracks and it looked as though one of them was a positive electron but that he thought that perhaps Professor Millikan wasn’t convinced and didn’t want it published or something like that. At any rate, E. T. Bell said, “I said to him, you go ahead and publish that. Send it in for publication. Don’t fool around.” So Carl sent it in. Now bow much of this is true — whether E. T. Bell — but this was at the time, you see; it wasn’t long afterwards.
That’s very interesting. You think that Millikan definitely was opposed to his sending it in?
I just don’t know, but I can also tell you a little anecdote. We are now in the (Krutch) laboratory and it’s connected to the Crellin laboratory where my office was for ten years, and then beyond that is Gates where I used to work before that. I worked also in the astrophysics building in the ‘30’s when Gates became too full to allow me to expand, and in ‘47 I moved into Crellin. Along about — when was it? — ‘37, I guess. Was it ‘37 when the Crellin Laboratory was being built? I guess so. There was a steam shovel digging a big hole because it had a basement and sub-basement, and in this big hole was the steam shovel. On the steam shovel was a sign, “Jesus Saves,” that somebody had painted, you know, but one morning when we looked down, there was the sign, “Jesus Saves, but Millikan Gets the Credit.” [Laughter]
Of the various physics developments, was the neutron a concept of difficulty? Was that generally and immediately accepted or not?
Well, I think so, I think it was generally and immediately accepted. I accepted it. I had read the papers by [W. D.] Harkins in 1920, 1921, 1922 in which he discussed the structure of nuclei in terms of protons and neutrons, using the word ‘neutrons.’
Yes, the word had of course occurred even earlier; I know it was used at the turn of the century, for instance, but then it was used to mean a combination of a positive and negative electron. Was that the sense in which it was used in the ‘20’s?
It’s hard to tell what Harkins meant in these papers and for awhile as I recall, in 1920, perhaps he talked about the nucleus as involving protons and proton-electron pairs or proton-electron combinations, but then he began using the word ‘neutron’ and I don’t know that he ever said it isn’t protons and electrons that are present in the nucleus but protons and neutrons. He did have a lot of interesting discussion of the properties of nuclei, the number of extra neutrons, that is, the neutron excess over protons as a function of atomic number, and he was trying to understand nuclear structure in a way that was ahead of his time.
Was there much discussion of the problem of the electron in the nucleus? Or was this celebrated difficulty really exaggerated afterwards?
I don’t remember that there was much discussion, and I just talked about the nucleus as made up of protons and electrons without worrying about what the electrons were doing there. Once I think — my memory is that I asked myself the question, if we take the electromagnetic size of the electron and the electromagnetic size of the proton, there is such a great difference in size, assuming that all of the mass is electromagnetic mass, that it doesn’t seem reasonable that the nucleus should consist of electrons and protons.
The idea that the mass of the proton was entirely electromagnetic was not a common one in 1925.
No, I don’t think it was, but I think that I’m right in saying that — you see, there was discussion of the electromagnetic mass of the electron. This comes out in connection with the Compton effect, too, in some way. At any rate, I connect it with the Compton effect. There was much interest in the neutron. Dickinson, you know, began doing neutron experiments immediately. I don’t remember that he published anything but be immediately built a big sphere of paraffin to slow down the neutrons and do capture experiments.
Oh, he was doing capture experiments.
Yes. This was probably after Fermi had published some papers. Dickinson was a remarkable fellow; as soon as the Raman effect came along he began doing Raman effect work and he got the first pure rotational Raman lines. Dickinson, Dillon and Rasetti. That work was done in the Gates Chemical Laboratory.
I ran across a review of The Structure of Line Spectra by Shenstone; do you remember that?
Yes. Well, there were two things as I recall. He published it in 1930 or ‘31.
It was in ‘30.
First, he criticized us for not using the new nomenclature; well, the book was in press when the new nomenclature was accepted. That was capital L, S, and J for the resultant quantum numbers, the resultant angular momentum quantum numbers, and unfortunately we had written the book Just a little too soon to get the nomenclature in. And second, he said that reading this book would give you the idea that — this is thirty-four years later, or thirty-three and a half — spectroscopy was a completed science, that you understood everything and that this isn’t true; there are still lots of things to be discovered.
You have a colossal memory. The exact quote is that you give the “impression that it is a closed chapter in physics.” [Laughter]
Yes, well that may be. I felt that we were writing a textbook and you know, it may have done me some good because now of my freshman texts reviewers often say that one nice thing about the texts is the number of times that mention is made of things that aren’t understood yet. It may well be that this book on spectroscopy should have discussed more of the problems that weren’t yet understood. Well, of course I was awfully pleased that so much was understood that hadn’t been understood say four years earlier. I thought it remarkable that such a fine development of theory should have taken place as to permit spectroscopy to be discussed in such a penetrating way as compared to what Foote and Mohler had done eight years earlier.
Well, I think that part of Shenstone’s criticism had to do with the fact that there was some material in Hund’s book that hadn’t been incorporated. I don’t quite recall the details, but that some of what Hund had said had not been incorporated in your book although Hund’s book had been written some years earlier.
Oh, yes, that may be. Well, I thought of it as a textbook for a one term course, you see, and I gave a course once and then Dr. Noyes told me that Millikan had complained to him about physics courses being given in the division of chemistry and chemical engineering and that I shouldn’t give the course anymore.
And what effect did that have?
You didn’t give it anymore.
But I incorporated it into my course in quantum mechanics. They didn’t complain about my giving the course in quantum mechanics. Millikan of course felt that he was a spectroscopist. Millikan and Bowen made great contributions in their ultraviolet spectroscopy. This shows that the United States wasn’t lagging in experimental physics in 1920 and thereabouts, although we were lagging in theoretical physics.
Oh, yes. We were spoken very highly of by the European writers.
Well, all along, in the 19th century too, American spectroscopists and other American experimental physicists were making important contributions. Michelson-Morley.
Well, Rowland too.
Yes, with his gratings, and Henry too, so far as that goes, or Benjamin Franklin! [Laughter]
Well, they get fewer and further between.
And in theory we had one great man, Gibbs. I was pleased that the Nobel Foundation in their book on Nobel Prizes say that it would have been thoroughly justified to have given Gibbs the first Nobel Prize for chemistry.
Well, he was considered, was he not?
No, I don’t think he was ever nominated. He died about 1904.
Yes, he died too soon.
He wasn’t ever nominated.
It was the X-rays that got him then?
Yes. The importance of his work was being recognized around the turn of the century but there had been quite a delay all right.
I think it was better known than is usually said; he was quite methodical in sending his reprints to the parties where they would be most recognized.
Ostwald. had his [Gibbs’] papers translated into German, and when Americans came to study physical chemistry he liked to give them these papers in German and let them wade through, never knowing that they had been written originally in English! At least this story is told of some Americans.
Well, it rings true to Ostwald. I think that I’ve exhausted my questions.
Here’s Darwin, here are my notes on Darwin in 1923, spring. So it was ‘22 — ‘23 that he was here. My notes aren’t in very good form but you can see what I was learning during my first year as a graduate student when I had studied no mathematics for a long time.
I was very much interested in your observations about Bridgman concerning operational significance. Your interests are apparently for the practical, for that which can be tested and if there is a theory which can’t be translated into operational terms, you’re not particularly concerned about it.
That’s right, and I would agree with Bridgman that it’s essentially meaningless if it has no operational significance; it becomes just a matter of semantics.
It’s a difference that makes no difference.
You asked shout Tolman: Here’s second quarter, 1922-23; [reading from notes] Tolman, “the classification of the sciences, concepts, ‘what is this course?’ sciences, quantities, space and. time [and other topics, not audible]” — well, that seems to be the start –- “mathematical physics, universal discourse, indefinables, definitions, defined terms, postulates (introduction theorems), internal criteria, external criteria, logicalities.”
That’s a lot of words; I hope you didn’t have to commit those to memory!
I don’t think so. “Two kinds of magnitudes: extensive can be divided, intensive cannot be divided. Quantities: scalar, vector multiplication, inner products — well, you see, he was perhaps a little slow in getting started. Here are Tolman’s rational units — I remembered this, you see — (Lewis and Adams’) ultimate rational units. Stefan’s constant — they tried to determine Stefan’s constant in this roundabout way. The entropy, the Sackur-Tetrode constant; they got a value which was wrong for the Sackur-Tetrode constant. This would make Planck’s constant the square root of 8/l5ths pi to the fifth — Planck’s constant is derived on this theme. Yes, I don’t know how it comes out. I don’t know what he’s getting into here –- “relativity of size”; this is the “theory of similitude,” he called it, too. And “relativity of motion in free space,” so he discussed theory of relativity for awhile.
Larmor made a good deal of that argument of similitude.
Here’s an examination, “Introduction to Mathematical Physics, second quarter, 1923, Linus Pauling.” I got 94. And this apparently was on this course; perhaps it was called ‘Introduction to Mathematical Physics.’ This is Tolman’s writing. Yes, well I just don’t know what I was up to. I probably was working some problems rather than doing research. Here’s a course on advanced calculus that I took my first year here, my notes on it and the examination. I don’t know what I got; it doesn’t seem to have a grade on it. Oh, 4 — I think 4 and 5 are grades; this I think is another final examination. 5 is the maximum then; they give A’s, B’s, and C’s now. Kinetic theory — Millikan, 1923, fall. Well, I took a course from Millikan at the beginning of my second year and my notes begin to look a little better; I was getting neater.
Yes, you said that Millikan himself was a bit disorganized.
I have lots of notes that are in pretty good shape like this. Here is some of my early stuff on —. Well, let’s see, here is a course that I apparently took in radiation chemistry from Dr. [J. H.] Ellis; that’s the one that involves Foote and Mohler. It cost four dollars and a half, which was an important criterion. R. W. Wood, Physical Optics, Planck’s Warmestrahlung — I think I bought Foote and Mohler but not Warmestrahlung, and that wasn’t bad. [Continuing to look through notes]. Here Tolman seems to be teaching something; seminar on radiation chemistry. Well, you can see the sort of things that were going on in the chemistry department here in 1922 and compare that with a standard institution at that time.
That’s true; that is rather remarkable.
I got 76 on that, an exam in radiation chemistry.
We have his grades here from high school and college.
Electron pair bonds — here is the course that I gave the first term, in the fall of 1930; it’s sort of an introduction. This is “‘The Nature of the Chemical Bond and the Structure of Molecules,’ written for Professor A. A. Noyes in heartfelt appreciation of his unfailing kindness,” and so on, 1934. He was ill then, beginning to be ill and I think I wrote this just to cheer him up in a sense. ‘Honor section of freshmen.’ I was in charge of the honor section of freshmen in the spring of 1925 and there were eleven men there in this honor section. Now I put [E. M.] McMillan at the top; and Robley Evans is Professor of Physics at MIT and has a big 14.50 or 16 dollar book on nuclear physics, Robley D. Evans. [G. T.] Harness was Professor of Electrical Engineering at Columbia University but he’s in southern California now. Lombard, I don’t know where he is now, but he was on the staff here for awhile and then went to Washington during the Second World War in charge of procurement of airplane engines. Pierce I just don’t know about. Pierce of General Telephone attended my course; this is [Bert] Pierce, another one. I don’t know what’s happened to him.
What was this course?
This is the honor section of freshman in chemistry. This was for research, and the only one who published his research was McMillan. His first paper was done during his freshman year; he collaborated with me. Here is his first paper, Edwin McMillan. You see, these are all researches that these boys did, these freshmen, and each of them was attacking some problem, the answer to which wasn’t known. [In the meantime Pauling has brought out his correspondence from the period and begins reading from the letters.] “It is true that the arguments I used here are very complicated and not too straightforward, but I think the second correction factor is really required and is of approximately the form I have given it.” This is the paper that I told you about, you see. “If Prescott prepared any pure zirconium carbide, even in powder form, I think it would be worthwhile to try to determine its crystal structure, for it might be of importance in regard to the theory of tetrahedral type crystals developed by Grimm and Sommerfeld.” You received a reprint of this unless it went astray. “Crystal interpretation is difficult; I’m hoping to do something on it soon. I have talked with Fajans and also with Knorr — you mentioned Knorr —” who has some interesting cases of non-polar compounds, metallo-organic ones. I think it might be worthwhile to prepare a review of the evidence about the dynamic model of the non-polar bond.” This is July, 1926; I’d been there about two months in Munich. “I feel that Grimm and Sommerfeld’s theory somewhat expanded may get support from many crystal structures. Herzfeld, who is a physical chemist as well as a physicist, is going to stay in America at Johns Hopkins; Professor Sommerfeld was sorry to lose him.” Of course he’s been at George Washington now for a long time. “We went to Zurich June 22-26 for a congress on magnetism called by Debye. Professor Sommerfeld presented my work on the influence of a magnetic field on the dielectric constant of HCl. Later W. Pauli, Jr., showed me that probably the effect definitely predicted by the old quantum theory would not be predicted by the new quantum mechanics.
So you hadn’t that part to begin with.
No, I didn’t have that … I didn’t know what quantum mechanics would give, I think, at that time because I hadn’t yet started. I’d heard these lectures on matrix mechanics; I hadn’t yet heard much from Sommerfeld in the way of [quantum mechanics]. I don’t remember whether he was giving this course, but it wouldn’t have got that far anyway. “The fact that Mott-Smith did not find the effect is accordingly good evidence against the old quantum theory and for the new.” Now that means that so far as I was concerned there was still probably some question about new quantum mechanics, you see, at that time.
Yes. A very informative letter.
“I am now working on the new quantum mechanics for I think that atomic and molecular chemistry will require it. I am hoping to learn something about the distribution of electron orbits in atoms and molecules. I talked with Professor Ewald in Stuttgart about crystal structures,” and so on. That’s all about crystal structures then to the end. Here is November 22 — it’s about that paper. “There is a difficulty at the point where I introduce this correction even though Zwicky does not see it. The point is, however, a difficult one and my treatment is rather physical and intuitive than mathematical and rigorous, so it is not surprising that Dr. Bateman probably did not understand it. Dr. Tolman has expressed the justified criticism that I have changed the physical picture underlying the mathematical treatment in order to introduce this correction, so that I am using the results of two idealizations. This is exactly the reason that has led me to believe that probably the paper should not be published.”
What is this paper?
That’s that extension of the Debye-Huckel theory. Still I continue to think that it probably should have been, now. Well, I don’t know then. “We were most glad to learn of the travel prize candidates and to know that we can hope to see perhaps four of them here. My plans for the summer are unsettled. Perhaps it will be worthwhile to visit both Copenhagen and Zurich for reasonably long periods. Professor Victor Henri has just been here delivering two lectures on his study of molecules such as H2CO with band spectral methods. He is going to America in February,” and so on. “Professor K. P. Compton spent a week here; he is a fine man. He and his wife brought their two children along. My respect for my wife’s good sense has been steadily rising, for I argued strongly against leaving the baby.” We left him in Oregon.
On the whole trip?
Yes. He was just a year old when we left or would be in 10 days; perhaps he was just a year old and he was two and a half when we got back. “I am now working on the prediction of the physical properties of atoms and monatomic ions. I intend sending this paper to the Physical Review.” That was the Royal Society paper Sommerfeld wanted.
Was it Sommerfeld who suggested it go to the Royal Society?
Yes, he said he had just been elected a foreign member and he felt that he would like to do something in connection with them so that, if I were willing, he would submit this paper.
And it’s perhaps the only one that he ever submitted to the Royal Society, so far as I am aware. “This semester I am devoting my time mainly to research. Further than that, I attend Sommerfeld’s lectures two hours a week in which he is presenting the new wave mechanics systematically, and two seminars. I have not thought it worthwhile to hear Sommerfeld’s lectures on mechanics nor Fajans’ rather elementary atomic structure lectures and seminars for chemists. There is now one other American with Professor Sommerfeld, an experimental physicist from Columbia.” I don’t know who that was. “I have just decided that I may have been using j instead of j plus 1 in my equations and I must look to see.” I don’t know why I put that in; I’m not sure he could tell what equations they were either… “McMillan brought in the paper describing his work which I am enclosing herewith.” This is that paper; I think I suggested that he write it up.
Edwin McMillan. I don’t know who that [letter] is from; it’s to me. It may be from A. A. Noyes; it probably is… [Several voices] This is [a letter] from my wife to Dr. Noyes. “Linus says that he wrote to Mr. Moe in October about his reapplication and Mr. Moe said it was not due until the 5th of February. However, I believe Linus intends sending it sometime this month. He is groaning at present because he must either type a forty page article himself on the rickety machine at the institute” — that’s Sommerfeld’s institute –- “or else pay seventy Marks to a typist in town. We haven’t decided just what is to be done about it.”
What was done about it?
I don’t remember, but my wife may. We were on a short [budget].
That’s a long paper, too.
Yes. Here’s a paper. “Prediction of the physical properties of many electron ions. Mole refractions, diamagnetic susceptibility and extension in space” [Proc. Roy. Soc. 114, 1927], that’s what it was. “The delay arose from my having to type it myself. The typing agencies require double hourly price and also double time for typing in English. It takes twice as long and they charge twice as much per hour.
So it’s four times more difficult than German.
Some of the keys on German typewriters differ from ours which explains why I occasionally put in place of a comma, etc. Here A. A. Noyes says two copies, one to Dr. Millikan, and he’s put ‘omit’ so A. A. Noyes had my handwritten letter typed and a copy sent to Millikan, but he had this deleted.
That was too much levity for Millikan!
“This paper will, unless some unforeseen circumstance arises, be sent to the Proceedings of the Royal Society in a few days. I have not forgotten your advice about publication in our own journals. Professor Sommerfeld became a foreign member of the Royal Society last spring and I believe that he feels he should submit some paper to the society. I have felt that his kindness to me required me to act in accordance with his desires.” And then there’s more about publishing – ‘theoretical properties’ —. “I am learning a good deal of the foundations of quantum mechanics from Sommerfeld and I hope to get an idea of the opinions of Bohr, Heisenberg, Schrodinger, and of others.”
Now if we can find the letter in which you describe those opinions we will have a treasure.
“I have just realized that the time will soon be here when the Institute [i.e., Pasadena] as well as other universities makes its decisions regarding the staff for the next year, so that definite arrangements regarding my position and salary will also soon be made. I have had no offers from anyone for I have thought, and accordingly expressed myself as believing that I would return to the Institute. Some people seem to think that work such as mine, dealing with the properties of atoms and molecules, should be classed with physics but I, as I have said before, feel that the study of chemical substances remains chemistry even though it reach the state in which it requires the use of considerable mathematics. The question is more than an academic one for the answer really determines my classification as a physicist or chemist.” He may have asked me. This is Dec. 17, 1926. And here is my report, my application for a second Guggenheim Fellowship which describes what I had done and the papers I had published. [Reading] “Proposed Plan of Study”: “I plan in addition to make a study of the statistics of the wave mechanics” — I wonder what I meant by that? — “with special reference to the explanation of the anomalous specific heat of hydrogen.” I know what I meant: I mean quantum statistical mechanics.
Yes, you had the same remark in the letter you wrote to Schrodinger as I remember.
And what happened was that David Dennison came by and said that he had discovered the answer and he published his paper, which was that there is a frozen in equilibrium between orthohydrogen and parahydrogen, that it’s a slow —. You see, Tolman and Badger had published a long review paper in which they tried almost everything and still couldn’t account for the hop in the specific heat of molecular hydrogen. The one thing that they hadn’t tried was a frozen equilibrium, a frozen in equilibrium. They recognized the difference between the even and odd states and I think knew that there were forbidden transitions, but it just didn’t occur to them that they were so forbidden that they didn’t occur at all in the time of the experiment. [Looking through papers] The proof sheets of my paper in Zeitschrift that we were thinking of.
Oh, yes. Did you write that in German?
Well, I think I wrote it in English and wrote it in German both and then I took it to Sommerfeld who asked Karl Bechert, his assistant, to correct it; and Bechert looked at what I’d written in German and said he thought it would be easier if he translated it.
Did you get to the point that you were able to participate in the seminars and technical discussions in German without trouble?
Oh, yes. I gave seminars in German after about six months, I think, and gave lectures. During recent years I’ve given several, fifteen or twenty, lectures in German over in Germany, even with no practice. Well, here’s the first page – there’s an extra “o” – that’s my typing. Apparently Dr. Noyes kept the first page of the manuscript and threw the rest away. And here’s a letter from Sommerfeld, 1926, to the John Simon Guggenheim Memorial Foundation. A reference for me — I suppose be sent the copy to A. A. Noyes when I applied for renewal o the fellowship.
[Reading] “An extraordinarily productive scientific Kopf.”
[Chuckle] I hadn’t read this; I’m not sure that I’ve ever read it.
In Sommerfeld’s Current Biography entry he says that “when Linus Pauling was in my classes, I learned a great deal, and he learned as much as I did.” …
You know, plenty of people have said that they doubted that I should have gotten the Nobel Peace Prize.
Well, Life Magazine of course —
“The weird insult from Norway.” What I’m looking for and not succeeding in finding is a statement that Hans Bethe made. I have it somewhere around. Hans Bethe was and in fact still is chairman of the advisory committee to the President and as good a physicist as there is, I think —
Here’s your high school blue book in chemistry, but it probably wouldn’t say anything about the quantum theory.
I’m looking for the February and March issues of the publication of the Society for Social Responsibility in Science. These were on the social responsibility of scientists and in the third article he [Bethe] said something like this: “There are three classes of scientists who were involved in the Bomb Test Treaty. The first is those scientists who were opposed to bomb tests because of the damage done by radioactivity; they are represented by Pauling who received the Nobel Peace Prize for his work, and I think rightly,” he said. Then he said, “Pauling, by his speeches was responsible for influencing public opinion about this matter not only in the United States but also in many other countries, and if it had not been for the pressure of public opinion the treaty would not have been made.”
Did you say Bethe? That’s very nice, that’s very nice.
Yes, Bethe. Then he said, “The second group is represented by the scientists on the president’s Scientific Advisory Committee. They were left unimpressed by the arguments about damage done by fallout, but felt that the possibilities of devastation in a nuclear war were so great that it was necessary to call a halt and that the Bomb Test Treaty would be the first major step. Then the third group was represented by Teller.” [Laughter]
And how did Bethe characterize that?
Well, I don’t remember. I’ve forgotten what he said about them. That’s around here somewhere. [Searching for article] That’s funny; here’s a letter from Heisenberg to McGraw-Hill thanking them for a book. Here’s a letter from Sommerfeld, but it’s 1937. “Sie sind jetzt als Head of Chemistry Department ein grosses Tier; und Millikan ungefahr gleich gestellt!” Well! Approximately equal to Millikan! “Es ist wirklich bemerkenswert wie hoch in USA der Theoretiker geschatzt wird.”
Yes, that’s very nice. What is the date?
1937. I had become the Chairman of the Division of Chemistry and Chemical Engineering. “Ich bin dauernd damit beschaftigt, meine Wellenmechanik neu zu bearbeiten.” He kept working away. Here’s an Einstein letter. [Continues to look through correspondence] For years I wrote to Goudsmit, “Dear Sem, S-e-m” because he had told me when I met him that his name was ‘Sem.’ Only after many years when I saw him again, and after he’s come to the United States and his accent had been corrected, did I discover that he was just saying, “Sam.” Samuel is his name.
That’s quite a nice letter!
I guess you don’t want these letters about publishing that book. [Reads] “In New York we found Oppenheimer” — this is 1927 –- “who was an excellent guide for us.” — this is from Goudsmit. “He had already a hotel for us so we did not go to the Prince George. In two days and a half he showed us as much of New York as possible.”
Well, there’s probably a good deal about contemporary physics in that exchange.
[Reading] “I give here a lecture on spectral theory. This lecture contains just the things I have written in my dissertation, thus I know now exactly what is wrong in that book and what may be useful. Randall, himself, and [R. A.] Sawyer, visit this lecture, too. Thus you comprehend that I try to do it as good as I can. This lecture has learned me now exactly which parts of ‘term-zoology’ are difficult to understand for beginners. Therefore I think it will be necessary to re-write my thesis for the greater part; you know that I had to write the whole book during the short time that I was in Copenhagen.” And then he goes on: “We further must introduce some more things. I forgot, for instance, to tell something about the Stark effect. The end is too compact and does not contain enough. I have only one page about Roentgen spectra.” Well, I wrote a whole chapter about Roentgen spectra. And it had a lot of things in it that had never been published anywhere else, actually — treatment of internal and external screening, discussion of energy levels that never —.
Was there any compass you were asked to work in for that book, by the publisher?
I don’t think so. No, I think I just wrote what I thought would be a good introduction to the theory, for the vector model especially. One interesting thing that you may not know is that I guess I introduced the proposition system into tin United States.
Yes, in doctor’s examinations.
Oh, the Dutch theses?
The Dutch Stellingen. In 1935, I think it was, I’d been talking about these propositions. The doctor’s examinations were pretty boring, for the faculty, anyway. One of my students named Harker, David Harker, volunteered to prepare some propositions. So I said, “all right,” and he brought in about four propositions. This was such a success that the division of chemistry and chemical engineering here required from then on that students prepare and submit a set of propositions. Then, when Harker went to Johns Hopkins, he got them to introduce the system there. Then other students went to Berkeley and various other places so that it’s rather widespread. It even has spread to some physics departments. I wrote a paper about it. One of my papers is on the use of propositions in doctor’s examinations.
Do you encourage the type that Goudsmit used in which he threw in one or two about Egyptian hieroglyphics?
Yes, what the Dutch called the 13th proposition, we encourage that, too. One of my students had a proposition that the Southern Pacific, instead of having trains over the Tehachapi, should run busses from Los Angeles to Bakersfield connecting with the train there; and a few years later they did. One student had a 13th proposition: “It would be possible for the chemistry division to give two more graduate fellowships without any increase in the budget.” When he was asked, “How could that be done?” he said, “Fire both of the janitors in the building and hire one good one.” He was complaining about the janitors. Well, I went down into the room in which our seminars used to be given, and opened the door. It was dark; I turned on the light, and there were the janitors sitting in the dark. Just sitting there. These are the propositions. I stopped collecting them after a while but for quite a while I — Oh, no, these are examinations. I guess they are a mixture of examinations and propositions. Well, what’s happened to my propositions? Those are examinations. I think I got some propositions in – [Goes through papers] Well, I don’t know where my propositions are. As I say, I wrote a paper describing the system. Well, you’ve about exhausted your questions, have you? [Pauling reads a dozen post-1935 propositions for candidacy and doctors’ exams.]