Oral History Transcript — Robert V. Pound
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Robert Pound; May 23, 2003
ABSTRACT: Some of the topics discussed include: his early life and education; interest in physics; his only formal degree, a Bachelors from University of Buffalo; from college to defense work and Submarine Signal Company; his work at the MIT Radiation Laboratory; the Harvard Society of Fellows; the discovery of nuclear magnetic resonance in bulk matter; the Bloembergen, Pound, and Purcell paper (BPP); the Pound Box, NMR patent issue; applications of NMR; after the war, writing Rad Lab books; Chicago Federation Group; nuclear quadruple moments; nuclear moments; alpha-gamma correlations and gamma-gamma correlations; becoming Assistant Professor; implications and influence of Mossbauer's work; Glen Rebka; gravitational redshift; Physical Review Letters controversy; Victor Weisskopf; the Harwell group in England; the gravitational redshift experiment; Nobel Prize; heating with microwaves; life as a professor at Harvard; Julian Schwinger leaving Harvard; overview of his career; physicists he has known; changes in the culture of physics; etc.
Session I | Session II
Rigden:Okay. It is now the 23rd of May. We are again sitting in Professor Robert Pound's office here on the fourth floor of Lyman, and we're going to pick up where we left off yesterday except to start by my asking Bob if there are things that have occurred to you since yesterday about the things that we discussed and you may want to add some items.
Thank you. Yes, it occurred to me that in connection with my first coming to Harvard as a member of the Society of Fellows, I came unofficially — well, I was already appointed, but I took a leave of absence for the first year from July '45 through that year because I had to stay at MIT to write the books. But I did come to Harvard and attend the newly started graduate courses that were now expanding because of postwar. And I audited — because officially as a junior fellow I wasn't supposed to take courses for credit but I could do anything I wanted. So I listened to all of those courses, including three years worth of Julian Schwinger, who started from scratch, Newton's laws and the like, and went all the way through the highest level of then known nuclear physics theory. And you know, all the other people in Cambridge were there, people from MIT, Herman Feshbach and John Blatt and so forth were a part of that audience, and all our graduate students were there, like George Pake, Nico Bloemberg and etc. And the funny thing is, George Pake has written this up saying he felt so intimidated because he found these courses very difficult, and then he discovered that most of the audience were professional guys from MIT and therefore as a first year graduate student he felt a little better about not — So anyway, but then the other thing I thought I should mention is that the denouement of coming to Harvard officially in July '46 was to become subject to the draft, and I was immediately called up and our then beloved president, James Bryant Conant, had made the pronouncement that no one at Harvard under his administration would be allowed to request deferment for any member of the university, because in wartime this was in the interest of public policy, but that in peacetime egalitarianism suggested that there should be no such thing.
So I got called up in July of 1946. I had to get up at five in the morning to go over to Fort Banks in East Boston and — or I guess South Boston. I don't know. It's Winthrop I think, I'm not sure. But I had to go through the physical exam, and one of the things they had was a written test first, and I went through all this physical exam, and later in that morning the captain — I had to go and see a captain who was a psychiatric officer in the medical corps and he said, “I noticed your answers to the question was asked ‘Did you bite your fingernails?’ and you said ‘Sometimes,’ and how about, do you have sweaty palms?” And I said, “Sometimes.” And he said, “How do you feel about riding crowded subways?” and I said, “I'd much rather drive if I can.” And he said, “Haven't I seen you somewhere?” He said, “Do you belong to the Cambridge Association of Scientists?” Which was the Cambridge version or affiliate of the federation in Chicago. And I said, “Well, yes, I was on the steering committee.” And here was this Army Medical Corps captain going to our meetings. I had never realized. And so he sent me to his boss who was a major, and the major looked at the papers he had given me and he asked me, “Now you don't want to be in the Army, do you, by any chance?” And I said, “No way.” After six years off my route, I figured it would be quite a comedown. So he signed the paper making me 4F.
Rigden:Isn't that nice? Isn't that nice? So you were part of the Chicago Federation Group.
Pound:Oh yes, yes. Well, we were independent in a way, but affiliated therewith, because all those people that had come back — Bruno Rossi, Viki Weisskopf and even people like Percy Bridgeman came to our meetings, and Percy Bridgeman's — one pronouncement I always remember from there was he said he wasn't going to go and ask the government for money to support his research, not going to have them telling him what to do and so forth.
Rigden:Was [James] Franck from Chicago active at that point?
Pound:In Chicago I think so, yeah.
Rigden:In Chicago huh?
Pound:Yeah, but you know, the people from Los Alamos had come back. Ken Bainbridge was back and so forth. This was in the fall of '45 and going onwards to '46. And I stayed with — and Bernie Feld at MIT and Herman Feshbach, and that's where I first got to know Herman Feshback, who had been in MIT through the war but in another area. He wasn't in Radiation Lab. He was with [Philip] Morse and they did demagnetization of ships and things.
Rigden:Was Philip Morrison part of it? No, he was at Cornell then.
Pound:Yeah, he was at Cornell.
Rigden:Well that's very interesting. Did you maintain that connection?
Pound:Yes, for some years, because we used — Bruno Rossi had meetings in his house over the few years following after that, and most of the people that went there were MIT people, but I kept going.
Rigden:We're going to come back to that a little later. So you are now — we're going to move ahead, all right?
Rigden:I have just one question. At the NMR work, was the first work in the fall or December of '46?
Rigden:And that in a real sense had a determining influence on your subsequent years as a physicist. You've done a lot of work in the area of magnetic moments, and what I'm now trying to do, Bob, is connect the period from '45 to '60 when your famous experiment was done and in between '45 and '60 you did a lot of work in the domain of magnetic, nuclear magnetic properties, and a specific question I wanted to ask — and you touched on it yesterday, but what brought your attention to quadrupole moments?
Pound:Oh, the first concept, the first time I became aware was when, for one thing we had already looked at the relaxation of heavy water. And since we had developed BPP, the theory of that kind of relaxation due to the fluctuations, if you thought it was magnetic as it was in the case of protons in water because of the smaller g-value then it would scale and be very much longer, slower to relax for heavy water because of the smaller magnetic moments, but instead of being slower it's faster. And so we realized, as from Rabi's further experiments, that the quadrupole moment of the deuteron was the dominant effect there. So we did the same concept of the fluctuation of a quadrupole interaction in the molecule.
Rigden:So the quadrupole moment was interacting with the electronic —?
Pound:With the electronic nonspherical distribution. And so the deuterium relaxation is faster than the proton relaxation in heavy water. So that was the first realization that quadrupoles were important in this game, but then I had this — I. I. Rabi came to give a colloquium talk in which he described some of the more recent things in molecular beamery. And the particular thing that struck me was at the end of his talk he talked about the structures found in the spectra of things like sodium bromide and such diatomic molecules and in which the quadrupole splitting turned out to be showing up as a structure factor, and in fact he realized that that was a large interaction so that they could go to very weak fields and see basically the zero field and depend on the quadrupole splitting as the basis of the energy gaps that had been studied. And that struck me immediately, and after that colloquium I said to myself and to Purcell and others, “Hey. Can't that happen in solids that are not spherically symmetric?” and I immediately started trying to develop a system to try to look for that zero field quadrupole interaction or splitting.
Rigden:Zero field, so pure quadrupole.
Pound:Pure quadrupole. Well, it's not pure in the sense that the rf transitions are all magnetic, but the energy states are caused by the quadrupole interaction. So I think it's a misnomer to call it pure quadrupole interaction. Because there is also a pure quadrupole interaction thing in which you depend on the fluctuations to drive the transitions. And you can apply electric field things that will cause transitions through the quadrupole interaction, and that would be more pure quadrupole than what is usually used for it. Which reminds me. Did you talk to Norberg about my article you were going to —?
Rigden:I haven't yet. I haven't seen him since I talked to you. Well you said yesterday that you got scooped on the pure quadrupole.
Pound:Well, in the sense of success in doing pure quadrupole. Now I had already published a number of things, mostly in abstracts and so forth, on quadrupole structures in magnetic resonance, but I set my goal too high for the pure quadrupole thing. I decided I wanted only to deal with ionic systems, because I thought one could calculate the field gradient. And this was partly inspired because Rabi has always advertised the concept that the only quadrupole moment nuclear property that was known properly was the deuteron, which he had done. And he had a standing offer of a bottle of scotch or something for anybody that could measure a quadrupole moment properly. And I thought, “Here it is,” because I thought I can calculate — So this notebook or some other one nearby has whole page's worth of attempting to evaluate the 1 over R-cubed values for the lattice structures, and the one I was particularly concerned with, because it seemed like a nice clean case was mercuric sulfide. Cinnabar. And I got myself lots of mercuric sulfide. And I knew there were tables that suggested the quadrupole moment of mercury, mercury-201, and I could therefore if I could get a field gradient value for that structure I could predict the frequency. The trouble was, every time I summed these series I got not only a different number but often a different sign. It's a nasty business, because it doesn't converge. Because in shells you sum R2 and 1 over R3 and you end up with 1 over R which doesn't converge. So it was a mess. But you have to do the partitioning of the lattice in a certain way in zones in order to do it properly.
Rigden:Was the inconsistency just the long calculation and little calculational problems?
Pound:More or less, well it was, yes, that's right. I guess I went to different distances in the sums and so forth. So I, but I had built the apparatus to look for it and that was the first scanning spectrometer using a marginal oscillator kind of thing, and actually it began a little differently in the sense that I thought I was going to actually even see the variation in the impedance through its noise properties when you get a resonance, because the shunt impedance of a circuit would be reduced when you hit an absorption as well. So the Johnson would show that, so that was essentially driving the resonance with the thermal energy which — Anyway, so but after a year or so I sidetracked and used the same apparatus to look for magnetic moments of many things, because we found it was almost impossible to do with the conventional thing we were using otherwise. I mentioned yesterday how we tried to find it with the Bloembergen spectrometer apparatus we had built down in the basement. And it was studying this fluctuating output meter from the lock-in detector, and sometimes it would go like so, but you'd go back and it didn't do it anymore and things like that, so you could never — So I was the one that invoked this continuously scanning — what do you call it? — chart recorder way of looking at the spectra. And that's what made a big difference in examining spectra. I should mention my originating double resonance — satisfying one resonance and obscuring the charge in another component. Slichter calls the technique Pound-Overhauser effect.
Rigden:Well, would you agree it's accurate to say that the period between NMR, '45, and 1960 your work was pretty much focused on nuclear moments?
Pound:Yes, except that a very important diversion in that was that in the year 1953 when Anatole Abragam came as a postdoc, as a fellow on our Shell fund at Van Vleck invitation. We got together and we jointly realized that one of the things that the nuclear physicists were having trouble with was understanding the directional correlations of gamma rays, alpha and gamma rays and so forth B alpha-gamma correlations and gamma-gamma correlations, directional properties. And that year we had a very intensive collaboration and I particularly made the point to Anatole Abragam that in a liquid state the quadrupole fluctuations would be a dominant relaxation mechanism, and together particularly with his help we came up with a very elegant group theoretical basically, or a matrix mechanics basically image of relaxation of many different multipoles in nuclear distribution, not just in that dipole distribution but for quadrupole and so forth. Because in directional correlations, depending on the spin value changes between a couple of levels, you get radiations at various higher level multipoles, and that paper we wrote jointly in the summer, well in the spring of '53 goes through that in considerable detail. If we had —
Rigden:Let me just say, that paper is “The Influence of Nuclear Quadrupole Moment on the Alpha-Gamma Angular Correlations.”
Pound:That was the first one.
Rigden:And then “Angular Correlations from Liquid Sources.”
Rigden:That was '53.
Pound:That's the one. He made my — my name came first on that paper I think. It's the only one of that bunch. When you collaborate with a man whose name is Abragam, you don't get to be first author very often unless you have a dominant condition. And but then the big paper was about all of those things. It was in Physical Review, whereas those others were Letters I think.
Rigden:And that was “The Influence of Electric and Magnetic Fields on Angular Correlations.”
Pound:That's right. That's right. So that, you see, I think gave me a considerable leg up on understanding the Mossbauer spectroscopy when it came along. Because it's the same bloody thing. It's the combination of NMR and this, looking at it from a multiple point — Therefore we knew what kind of lifetimes, and a lot of the people that went into Mossbauer spectroscopy did not realize that you had that kind of relaxation issue and that the narrowest lines you could produce would be limited by spin-lattice relaxation.
Pound:Frauenfelder was our main competitor in that game by the way. He was still then —
Pound:Hans Frauenfelder. He was still in Switzerland, and he did some of the best early experiments on the alpha-gamma directional correlation and then on the indium-111, which was the sort of model of understanding this kind of business. Then in the summer of '53, I spent that summer working with Jack Kraushauer at Brookhaven, wherein we did some studies of cadmium-111 which was an isomer that didn't have to go through a chemical change in its decay. You see, indium-111 went to cadmium-111 in its decay, but then you always had the problem, does it recover from the electronic change that goes in that beta decay, is it an electron capture decay leading to chemical charge. And so I went to Brookhaven where we could make cadmium-111 by neutron absorption directly. And I got Abragam and I, I got the Abragams to have residence at Brookhaven that summer too, just before they went back to France.
Pound:And then I started an experimental program when I came home in which Gunther Wertheim was the first experimenter to carry that out, and he studied the directional correlations of mercury-199. I insisted at the time, because I was still pursuing the issue of the quadrupole moments properly to measure the quadrupole moments, so I wanted to use isomers, not things that decayed by chemical change. Because then you could put it in a lattice of its own type, whereas you can't do that with something like indium-111. So, but Frauenfelder had shown in their work that the recovery from the capture — or I can't remember whether it was electron capture or beta decay — but the recovery in the metal was fine. But in insulators they don't work because the chemical recovery is not fast enough. So that's why I think I was in a better position than most of the people that tried to follow up to the Mossbauer spectroscopy, for knowing these things, because some people wasted a tremendous amount of their time Bob Dicke in particular — trying to find the Mossbauer line of things with 44-second lifetimes. Because they had the image that the inverse of 44 seconds would be a really narrow line, and that the energy involved that would have given you a fractional of line width 10-22 or so, and when I published the first paper on iron-57 — no, it was before that. When I published that first letter on the possibility of extending the Mossbauer spectroscopy to that point, he wrote me saying, “I'm afraid it looks as if we're treading on the same research interest and maybe we ought to collaborate” or something. And I wrote him and said we already had the iron-57 with which we were going to go ahead and try to do the experiment directly. And oh his letter, you've seen that in my article.
Pound:His letter said sometimes he thought this was such a difficult thing that nobody in his right mind should try it. He said that in the bottom of his letter. But I was going to try it, and —
Rigden:Before we get into that — we will come back to that in just a minute — but before we leave the period before the Mossbauer-motivated experiment, you worked with magnetic dipole moments, electric quadrupole moments. Did you ever give any thought to a monopole?
Pound:Well, only as a sideline in the sense that I was quite aware of what Ed Purcell's interest there was. And of course I was also aware of the suggestions by people like Dirac and those. But the thing I had more — Oh, that's another thing I was going to mention, is that a driving force for what I chose to try to do in NMR was still my old interest in the atomic clock question. And the quadrupole, initially I thought, “Hey, this is going to give me a resonance line that's going to be better than any of these microwave spectroscopy ones” because I supposed that the line breadth would be the same as if it were magnetic resonance. And the frequency might be as high as a thousand megahertz. And so the fractional line width might be very competitive with anything else. And that's why I pursued only these very high frequency cases. Not just that, but also the fact that if I could do it with an ionic thing I would be able to measure — And you know that I made this suggestion then that the quadrupole interaction ought to be strong enough to produce nuclear orientation at low temperatures because the energy states are comparable with kT. And that's why I went to Oxford in the summer of '51. I got a Fulbright grant to go and help participate in research at Oxford in the Clarendon, and that's when Nicholas Kurti was in fact developing the first nuclear polarization experiments. And Jim Daniels, who was then his graduate student on the side was also pursuing materials that could have enough quadrupole interaction. In particular we were pursuing crystalline things with iodine-127, which ought to have had 1000 MHZ kind of splittings, and he was doing that as well as working on this high field low temperature nuclear orientation following the proposals of — well, some people claim that Gorter and Rose, but the actual best suggestion that they succeeded with was that of Brebis Bleaney who followed my idea of nuclear orientation rather than polarization.
Rigden:Do you know how to spell that name?
Pound:Bleaney? Brebis, B-r-e-b-i-s. He is one of my closest friends there along with Nicholas Kurti who died a couple years ago. But anyway, so I had a very interesting year there in the Clarendon Lab with those people.
Rigden:And that was what year again?
Pound:I left here. As I said, I had been helping, in a way helping Doc Ewen working across doing this Hall in the autumn 1950, because that quadrupole resonance search that I was doing was right in the same frequency band that we expected the hydrogen, interstellar hydrogen might be. So I had all that apparatus up on the fourth floor, on this floor here in this building whilst he was in the room across the hall, and I was technically his advisor during the period that Ed was away. Ed was in a study that was begun from MIT really, called the Beacon Hill Study I think, and it was for the State Department. Of course in those days nobody ever said what these studies were about, but this was about surveillance of some kind.
Rigden:You know, one thing we didn't cover, or I didn't ask. You were a junior fellow. When did you become a faculty member?
Pound:Well, I lost a year as a junior fellow, so I was only, even though I never went to graduate school and so forth, I was only a junior fellow for two years in action, in active version, because I stayed on at MIT that first year. And I was invited by Van Vleck in the spring of '48 to become assistant professor. So I became an assistant professor in July of '48. But I was still — it was supposed that I could have got a substitute year for the year I'd lost if I wanted to at the Society. And Crane Brenton, who was the chairman, was very friendly with me, and I told them that I had an invitation to go to the first Radio Frequency Spectroscopy Conference after the war at Oxford in the summer of '48. And I had never done any traveling on the Society of Fellows, so he extended the support for my travels that summer although my term had ended in July and I spent most of the summer and took my wife along and we went to Holland and then England and then France and then back to England and we had quite a wonderful time. And the important thing, it brings in Van Vleck again. Because it was impossible to get a ship reservation to go across in the summer of '48 unless you had some help. And Van, I talked to Van about this, who was party to getting me invited to Oxford and to report — that's where I — There's a paper, there's an —
Rigden:Okay. Continuing. You first described —
Pound:I first described the marginal oscillator and the observation of quadrupole splitting in crystalline solids.
Rigden:And this meeting, Radio Frequency Spectroscopy meeting, was where?
Pound:At Oxford University.
Rigden:Oh, at Oxford. Okay, okay.
Pound:That was at Oxford. But what Van did for me in addition, then was to get me invited to a metallurgical conference in Holland because the Dutch were giving priority on the Holland America line to participants in the conference. So I got to go there and we got our ship passage on the New Amsterdam going to Rotterdam and it was quite a wonderful experience. I had not ever traveled across the ocean on a ship before, and among the people on that ship were the Van Vlecks, Karl Darrow the APS Secretary and somebody else at high level from the — oh, I think Sam Collins of MIT, the inventor, the man that designed the helium liquefiers. They were all in first class and we were in cabin class, which was much better than the tourist class. They had three classes. And in our class as well was — the person we spent a lot time with was Charles Kittel, and he was at our table in the dining room, and I got to know Charlie pretty well then, and he was debating about whether he could possibly leave the Bell Labs and take an offer of a teaching job at Berkeley. And because he had this dreadful speech impediment.
Pound:And what he always did then was to pull out a little pad from his pocket when he was starting to get hung up and he'd write it down, and that would relieve him. But he took the job and has done very, you know, it worked out very well.
Rigden:He's done very well, yes.
Pound:Yeah, Charlie. So that was quite a trip. And there were a number of Dutch people we got to know on that trip. There was a man who was in a harbor transport business, a man named Peterson. We spent the evenings at the bar with him. We asked him was he in Rotterdam when the Germans bombed and, “Oh yes,” and “What was that like?” He said, “Have you ever pumped water into a grand piano?” And he hated what they had done to Rotterdam. He said all that new construction they had built which covered up quite a —
Pound:He said, “It's all banks and government buildings,” and he didn't like it.
Rigden:Well okay. Let's move now to somewhere around '59, late '59. You, from what I understand, when you saw the results of the Mossbauer work, specifically the narrowness of that line —
Rigden:You recognized immediately some potential. Why don't you just talk about that?
Pound:Well yes. You see, as I was mentioning, I kept looking for narrower things than say ammonia, which was the best resonant spectrum we then knew, and when I saw that I immediately extrapolated to the possibility that if one chose other — Well, actually it wasn't Mossbauer's work that I saw directly; it was that of the two groups that repeated it — one at the Argonne and the other at Los Alamos — and they both published in September 1959 Physical Review Letters.
Rigden:No no no —
Rigden:Oh, oh, yes, yes, okay.
Pound:No, I'm sorry. 1959.
Rigden:'59. Yeah, we're talking about Mossbauer.
Pound:1959. Sorry. Yes.
Pound:1959. They both published those repeats. I had spent that summer in a defense study group at La Jolla run by a man who was at the Scripps Institution. It was on oceanography well, it was related to oceanography because it was relating, it was called “Project Sorrento” and it was related to submarine detection. And we had all kinds of people there which included G. I. Taylor, the British hydrodynamicist I guess you'd call him, and I shared that room with Tommy Gold and —
Pound:Yes. He was an English physicist really, but then he became a cosmologist and he was party to that — what do you call it, continuous creation theory?
Pound:Yeah, steady state theory. But he'd come to Harvard by then. Actually he was already at Cornell. He spent a couple years here at Harvard first in the astronomy department. And George Carrier was in that group. So then I came — I hadn't been thinking too much and watching the Physical Review. When I came back it was Glen Rebka that called my attention to these two letters in the September 15 issue of Physical Review Letters, which was a newly then created publication then. And then because of that we came to my office and, one evening very soon after reading those papers, because I foresaw that there must be a better case. And we studied the isotope tables and came up with three examples that should be considerably better than the iridium case that Mossbauer and the Los Alamos and Argonne people had pursued. They were respectively zinc-67, iron-57 and germanium-73. We never pursued germanium because the data showed that it had a terribly high internal conversion coefficient, which meant that really nobody had ever seen the actual gamma ray in those days. They only saw the conversion electron. But its energy and lifetime were such that it's line should be naturally very narrow. And long after that some Bell Labs people had been able to pull it out and see it, but it took a whole month of data accumulation before you could get enough intensity, and it only came out when they finally made, developed a fancy solid-state high-resolution detectors that could separate that gamma ray from the X-rays. Anyway, so we immediately considered exploring the iron-57 and the zinc-67.
Rigden:Let me just pause here a minute. Did Glen Rebka bring that to your attention because he knew of your long-term interest in —?
Pound:No, he wasn't thinking in terms of the high-resolution aspect at that time. He was thinking in terms of maybe — well, we had been pursuing directional correlations, and here was something fairly closely related using nuclear interactions in solids you see. Because we were pursuing this business that I started with Abragam.
Pound:And he had spent. He was — let's see, he got his degree in '55, his undergraduate degree in '55 I think, and this was four years into his thesis work, but the year I was in France in '57-'58 he spent that whole time building elegant power supplies to get high stability and had charts on the wall showing how little drift there were in the output of the power supply and so forth. Frank Pipkin became his temporary advisor during that period. But Glen was such a — what do you call it? — perfectionist, that he didn't, he wouldn't push on with something. What we were trying to do is to develop many pieces of electronics to build what we call a coincidence device that allowed simultaneous observation of coincidences on the delay line at — I guess we call it a chronotron. This was before you had things like multichannel analyzers you see, so we had to devise that we were going to make a 10-unit thing to look for the directional correlations at different time delays at taps on a transmission line. Because that, our theory covered that. And so he was building all this apparatus to do that. And in fact he had a fancy chassis in those days, vacuum tube electronics, that was to be the central part of that system, but he needed something like six or ten of them, and we were able to farm that out and have them wired. He did all the mounting parts and layout of chassis but he had the wiring done by an outside company. And when he got it back he was furious because they didn't use — what's it called? — a eutectic solder? So that he could see that the solder showed. Eutectic solder shows a nice polish when it freezes because it doesn't break up into crystalline stuff, whereas this solder was bad. He just wouldn't touch this thing because he thought it was junk. And he would go through each of them and start re-soldering everything his way. But then when this other project came along, I sort of took over and provided some push — A lot of that apparatus was there. That's what put us one leg up, because we had a lot of things that could be adapted to this.
Rigden:Well when you saw these narrow lines, at what point did you suggest to Rebka that this might open the door for —?
Pound:Oh, right away when we saw that. I said right away — I guess maybe the first time I realized how it could happen was that a couple of weeks later than that first publication it was a publication by a man named — what's his name Husein Ylmatz? A Turkish friend who was always trying to contribute to relativistic ideas, and he had written an article that got published in Physical Review Letters suggesting a way of using lasers to try to observe redshifts — which I thought at the time that that idea wasn't very good in itself, but I said to myself, “There must be a way to use these narrow lines in the Mossbauer spectroscopy to get a redshift.” And we worried about that, and I never realized until Rebka mentioned just separating the source from the absorber you see and letting the gamma ray traverse the distance between.
Rigden:When he said that, did you have any sense of what the magnitude of the separation would have to be?
Pound:Oh yes. We immediately — it depended on of course what resolution it would be. I knew what the fractional effect per meter was. The letter we wrote and [for] which we got an awful lot of flack saying “you had no right to write a letter like that, you were plagiarizing” and we were told we were stealing because this idea had been kicking around. And it hadn't been published by anybody or heard by us, and you know Singer had published a proposal of putting atomic clocks in orbit to do this thing, and that's just, that's a simpler concept than adapting this and nobody had suggested it. Now if you've read these articles by G. Henschel, this German, he's a member of your committee overseas, the historian of science.
Pound:Henschel. He had this one which is called — well, I always liked his article in which he talks about the Conversion of St. John.
Rigden:I don't know that.
Pound:Oh, you don't? You know, Edward St. John had tried to observe the redshift back from the sun in the teens and came to the conclusion that there was no such thing. He couldn't find it in his optical spectroscopy in astronomy. And then somehow — the people took that pretty seriously, and somehow he got to realize that the spectrum from the Sun was rather more complicated and there were other causes that may have been a problem. So a couple of years later he started to say, “After all, it may be there,” though his first papers had said it wasn't there. So when Henschel reviewed these things, he called the paper “The Conversion of St. John,” which I thought was a very cute way. But in any case, he has articles covering the issue of the redshift up until 1965 or something like that. But he interviewed Mather Leibnitz, who was Mossbauer's mentor in Gottingen, and he asked him what did he think of this and he said, of course applying the Mossbauer spectroscopy to do a redshift was obvious. Oh, of course they thought about it, but they thought it was so obvious nobody would talk about it and so forth, but they never mentioned, you know, in Mossbauer's own papers he never mentions that this has a uniquely narrow resonance. He said its main B he said the applications that he cites is to observe nuclear lifetimes in a domain not easily accessible otherwise. He doesn't say anything about its being a narrow line.
Rigden:Well Bob, you have in the back of your mind for many years this atomic clock idea.
Rigden:But when you saw the Mossbauer lines you must have had in the back of your mind also this idea of testing — did you have this idea of testing relativity?
Pound:Oh yes, yes.
Rigden:When did that come into your thinking?
Pound:Well, that came in towards the end of the Radiation Lab days when I was developing atomic clocks. Well, I was really developing frequency stabilizers which I envisaged I could make into atomic clocks by using a reference instead of a cavity — a fundamental thing like the ammonia line or whatever. And so in the summer of '45 there was an article by J. B. S. Haldane summarizing the work of — and promoting — the work of that E. A. Milne, a mathematician at Oxford. And that's the sort of thing that kicked me off on thinking about these multiple time scales issues and something relativistic as an application of these high-resolution timers.
Pound:And that was actually in the American Scientist, the journal of the — was it the journal of Phi Beta Kappa?
Pound:Sigma Psi, yeah.
Rigden:So here is a wonderful example of the prepared mind. You saw these narrow transitions, and while Rebka was thinking of something else, you saw immediately another experiment that you could —
Pound:Well as a matter of fact Rebka came up with the desire to look for hyperfine structure when we got the iron-57 working. And well, before that we wanted, he had iron-57 in mind before we actually pursued it from that point of view as a possible way of looking at hyperfine structure. And a number of people had — nobody had seen any hyperfine structure in this kind of spectroscopy as yet, but Maurice Goldhaber visited our lab, visited this place about that time and we talked to him in the corridor and I told him we were thinking about trying iron-57 partly and he said oh his people, what's his name, Kistner was one of them, but the other one that — Andy Sunyar. Sunyar was going to pursue iron-57 to look for the hyperfine structure down there at Brookhaven. So we knew there were other people in the game. And as I told you once, I guess when I finally had — I got so enthusiastic that we wrote this up as a paper that got published in Phys. Rev. Letters, and I had a number of feedbacks from that, one very nasty one from Frauenfelder.
Rigden:And this was the first paper that you wrote —
Rigden:Essentially laying out the possibility of doing this.
Pound:That's right. And we envisaged that we might have to go to a mine shaft or something like that and so forth, because we put in the numbers for the two cases, iron-57 and zinc-67 for the width of the line as compared with the height that it would take to get that shift. But we never said that you would have to have that height. Because a lot of nuclear physics people assumed that you would have to have a shift equal to the line width, not thinking that by high counting rates and data and stable issues you could split the line into a very small part. That's what we realized immediately.
Rigden:This Phys. Rev. Letter was in October of '59.
Pound:Yeah. It was only a few weeks after we had first seen that phenomenon.
Rigden:And you really had data to report in early '60.
Pound:On the redshift, yeah.
Rigden:On the redshift. Then in December the New York Times picked it up.
Pound:That's right. Well, actually that man, Harold Schmeck, Jr. who wrote that up, he called me on the telephone sometime around early November and said his friends at MIT had been telling him about this project that I was into and he'd like to come up and talk to me about it. And a week or so later he came and sat and we talked, and then sometime he sent me a manuscript of what he wanted, proposed to publish, and that was maybe around the beginning of December. It was all going rather slowly. By the time that we had met, we had already succeeded in detecting the resonance of iron-57, and we simply mentioned that that had already been successful in that letter, in that article. But then he called me on something like the 10th or 11th of December to say that his editors were going to publish his article, and he had to shorten it, and he had submitted — he in fact, how ever did he get me? He got me a copy of what he proposed for it as a shortened version that would appear and wanted me to approve that before it got published. And I thought it was pretty well done. The main thing I had changed in the original thing that he wrote was to give more emphasis to the Mossbauer role in having developed this concept, not the concept of the redshift. But often in the literature Mossbauer gets credited with having done that you know, but I made sure that the concept of that nuclear physics line or resonance was given to him. And so then it appeared on December 13 on a Sunday issue on the front page. And that was a great shock to me.
Rigden:With Einstein in the headlines.
Pound:Probably, yes. As I used to say then, anytime you touch base with something that has to do with Einstein immediately the journalists pile out and I got proposals for buying pictures of Einstein and all kinds of crazy things. The actual letter on iron-57 was published two days later.
Rigden:In Phys. Rev. Letters.
Pound:In Phys. Rev. Letters, yeah.
Rigden:Let's deal with these two things separately. Both of them caused a controversy. The Phys. Rev. Letter, people were upset because they thought —
Pound:I hadn't done the experiment yet.
Rigden:— you should have waited until you had results.
Rigden:As you look back, would you do it differently?
Pound:I don't think so. I know that at the time when I was thinking and had realized that this could be, as I had mentioned somewhere, I ran into Ed Purcell in the hall and told him about this idea, and he was extremely enthusiastic about it, and Ramsey came along and he stopped Ramsey and he said, “Bob has this most elegant experiment in the world.”
Rigden:In your writing I think you said Ed Purcell said it would be the experiment of the century.
Pound:Something like that. That's right. And so they encouraged me to publish it. And I thought well, I hadn't really sensed any great reluctance to publish it, because if I had been known as a theoretical physicist there would be no question. And we always here, particularly this group of us, felt that we were not just experimenters, that we had — you know, Van used to tell us for BPP that we had outclassed theorists in that. Theorists should have been able to anticipate what we had discovered in fluctuation, but experiment drove our ideas. As Ed used to say about the NMR, that if it hadn't worked it would have been an outrage because it had to work. There was nothing newly discovered there.
Rigden:Did that Phys. Rev. letter —? You got letters from Dicke you said —
Rigden:Did that Phys. Rev. letter, do you think, clear the road for you? Did Dicke sort of drop out?
Pound:Well, he didn't — yes, he did drop out as far as pursuing the redshift, because he was having his student — Stevens? Was that his name? He asked if it would be okay to send his he wanted to send his student up here to find out how to do the iron-57 because he was going to put him on some other application, which he did. He put him on this spinning thing to look for an isotropy in space, and so that was fine. But you see, he had had him pursuing this silver-109 is it? It's the silver isotope that has about a 44-second lifetime, which was a completely unrealistic concept, because there is going to be spin-spin interactions that will broaden it way beyond that, and that dilution of the resonance through this broadening would be such it to kill its detectability. And people have been pursuing this. There have been people at Los Alamos, a guy named Taylor and others have been pursuing this kind of esoteric high-resolution example for years. It's still going on I think.
Rigden:And what was Sam Devons’ — why was he upset?
Pound:Because — [laughs] Yes. Sam had just come to Columbia for a sabbatical year, had taken leave from the group that he was with at Manchester. He held the professorship at Manchester that was once held by Rutherford, as you may know, and he had a group there that had been — he said they had spoken about this even in the summer of '59 at some conference. But it wasn't something that spread as far as I was anyway. But they were pursuing it, and we didn't know how far they had got, but they were pursuing it entirely on that limited concept that you had to have a line whose width was as narrow as the shift you would expect to produce, so they were pursuing the zinc-67 example. And they never got anywhere. One of the people on that group was named Bumbury and Bumbury is the name of Earnest's friend in The Importance of Being Earnest. He's the one who went to having an ill aunt was it or something like that, in The Importance of Being Earnest. Do you know that?
Rigden:I know the name. I don't remember the — Well, it's an interesting historical example. I think people are going to find this fascinating. Are you —?
Pound:I found that actually you know I got very upset over the fact that to Sam Devons — no, I'm sorry, that Goudsmit wrote that thing that was interpreted as being against me.
Rigden:That followed the New York Times, did it not?
Pound:Yes, that's right.
Rigden:So the New York Times, because you published in the media these ideas —
Pound:I didn't. My proposal had been published in Physical Review Letters in October.
Rigden:Well, but that's what Goudsmit thought.
Pound:He told me that that letter which he had had in his desk drawer ever since the Columbia press conference that was held on parity conservation, which made him furious at that time. And it hadn't really to do with me, but everybody out there assumed it had to do with me. Because after all we had done everything he required in the editorial before he wrote it.
Rigden:And what was the letter on parity? Wait. Let's just wait until we get a new tape. I'm going to stop this.
Pound:…week before it changed this time.
Rigden:Okay. Okay, we're back. Now Sam Goudsmit was upset following the New York Times feature article and you said he had a letter concerning parity. I don't know —
Pound:Well, in '56, was it, that the Columbia group did three different ways of demonstrating the nonconservation of parity.
Pound:Of course there was a theoretical group, then there was Miss Wu and the group at National Bureau of Standards, with Ernest Ambler in particular, and then there was the group that did the muon orientation with Garwin.
Rigden:Lederman and —?
Pound:Lederman and Garwin.
Pound:Yeah. And they held, before they actually even submitted to the Physical Review Letters they held a press conference to reveal this terribly important thing, and that's the one that violated all the conditions that Goudsmit argued should be held.
Rigden:So the parity paper was three years old.
Pound:Oh, that letter was, yeah, three years.
Rigden:And he had never published it.
Pound:He never published this letter that he wrote that he claimed he had in his drawer. I don't believe that completely because he must have modified it for the — because it didn't mention parity as such or any example as such, but the example everybody had in mind was this B and you know one of my colleagues and friends previously to that gave a colloquium talk at Columbia — I was told my old friend Alan Sachs who was chairman there — which cited me as a publicity hound because of that. And he had a slide on his colloquium talk showing me in some kind of cartoon that suggested that — Now I believe that was Hans Frauenfelder, because Hans Fraunfelder was our closest competitor for the iron-57 because he published almost exactly the same results that we did about a month later in Phys. Rev. Letters.
Rigden:But this was not the redshift.
Pound:It wasn't the redshift.
Rigden:This was the hyperfine.
Pound:It was just the spectrum of iron-57.
Rigden:Yes. Well, would that —?
Pound:But he didn't get all the satellite structure either. The people that got complete proper satellite structure were the people back at the Argonne Lab. Hannah, Hannah was the leader.
Rigden:Do you think this controversy colored the way people responded to the experiment?
Pound:Probably not in the long run. I think the main competition that we sensed and felt and knew about was the one with the Harwell people where John Schiffer who was from a Harwell group — no, I'm sorry, from the Argonne group that had repeated. He had been party to that experiment that repeated Mossbauer's original spectroscopy but hadn't extended it. They did extend it to another similar isotope to that and to lower temperatures than Mossbauer had, but they did not get a high resolution examples. So when he went on sabbatical leave to Harwell, he talked them into getting into the Mossbauer spectroscopy thing, and it was Ted Cranshaw [spelling?] there who thought he was unique in having suggested applying this iron-57 resonance to the gravitational redshift. And then they saw my letter, and that caused them to push much more hard because they realized they might not be alone. And the only person I sent a copy of our preprint, a preprint of our article on iron-57 — well, two persons — one was Rudolf Peierls because I had heard that he had a different view of how the Mossbauer thing came about. He had been in Columbia the summer before or something. And the other was Walter Marshall, who was head of the theoretical group at Harwell, and I had known his particular theoretical interest was in interactions in ferromagnetics and the nuclear spin interactions in particular, so I sent him a copy of that letter that we were the first ones to see some hyperfine structure in iron-57. And that's what Rebka wanted to continue to do more thoroughly, but our apparatus really wasn't good for it. I had a nice — you've seen that letter back from Walter Marshall, who was an old friend in a way. I had great attachment, because he had been here in the summer before visiting Harvey Brooks and the division. And I had told him — he was wondering if that Ford station wagon that he had acquired during his year here would be sensible to take back to England, and I said do it, and he did. And every time I saw him after that he was very grateful because he said it was wonderful having a big Ford station wagon.
Rigden:Listen. You gave a talk in January of '60 on the experiment.
Rigden:And Viki Weisskopf rearranged the program to allow some British group, English group to share this —
Pound:Well, that was Schiffer and Cranshaw I guess.
Rigden:But that was done in part because — I mean they were competing with you.
Pound:That's right. They had actually carried out and had gotten data on a redshift.
Rigden:Why did Viki do this?
Well, Viki was very aware — Well, he did it in the first place because they submitted a post-deadline thing and were scheduled to give their talk on Wednesday, whereas I had a longstanding commitment to give an invited paper, although I had no idea when I committed to giving the invited paper that I would be giving any data report on the redshift experiment itself. I was going to be reporting on the discovery of iron-57, because we assumed that we were unique in that. And so I was scheduled to give a full invited talk on the Saturday morning. And Viki called me to say that — Well, actually Schiffer called me when he arrived from England about Monday of that week and said they were coming to give a post-deadline paper on the results on the redshift experiment. And here we had started data taking on Sunday that week. And it looked as if it was working and so forth, and our data rate was basically eighteen times greater than theirs, so that in the one week that we had to run before I'd give the talk I realized I should have data that would be pretty good. Probably about an uncertainty of 10 percent due to statistics. So I was kind of decimated by the idea that they were coming to give the result that they had counted for thirty days. But they were using a 12-meter-high outdoor water tower on the site. And they got written up in The Observer, the English newspaper.
They were the front page of the magazine section of The Observer that week about how this group at Harwell was in competition with a group at Harvard University, and I said that that group was a man and a boy and so forth. Well, Glen was more than a boy, but still, that we did not have the facilities say of the National Laboratory that Harwell represented [correct word?]. Because they had the radio chemists and the machine people and so forth they could, who could help them do a lot of things that would be very, hard for us. So anyway, Walter replied that had he seen our paper he wouldn't have submitted theirs because they had also observed the resonance of iron-57 but they did not study the hyperfine structure; they only inferred it from the weak intensity of the absorption. And so anyway, they had pushed on, and I had a letter from Schiffer that said, “I think we probably should not exchange details as to how our experiments are going to work.” When I saw that I felt he thought he had a better idea than we had about how to do it. And it turned out he did have the idea of modulating the Doppler velocity as we had, but they did not have the idea of the need for inversion or the need for looking to using a system that could independently see distortions in the modulation system — which we called our monitor system. So we had much more overall control on our system already built in at that first run, with continuous calibration with a hydraulic moving system.
Rigden:We'll come back maybe a little bit to this, but why don't you now just describe briefly — describe the experiment.
Well, the experiment consisted of developing a source that was as strong and as unbroadened by other causes as we could make it. And it contained iron-57 — I'm sorry, it contained cobalt-57 electroplated onto a thin sheet of natural iron, pure natural iron which was about 2 inches in diameter. The dimensions are important because the amount of material you electroplate onto this thing determines how much activity you can get into it, radioactivity to get gamma-ray intensity. But you don't want so much material as to make an alloy out of the iron with the cobalt; you want a very low concentration. So that's why we had to have, in the later experiment we used a 4-inch diameter disk in order to use a larger amount of cobalt. And we also were concerned about the degree to which the cobalt was carrier-free as it were. The cobalt was created in a cyclotron at Oak Ridge through the intermediary of a company in Pittsburgh called Nuclear Science and Engineering. Anyway, I had a letter from Oak Ridge saying that they were so interested in the experiment that they had spent Christmas Eve running their cyclotrons, a special thing to try to make our source [unintelligible word]. And it was basically at the time the company was miscalibrating their intensity so they called it 400 millicurie, which is a pretty big source, have radioactive sources, but they later changed their calibration so it was really only about 250 but it was still the biggest source anybody had purchased. But they did not then have the facilities to do the diffusion themselves — once the cobalt was electroplated onto this iron disc they did that for us.
But then I had to take care of getting it diffused into the iron by heat-treating it in a hydrogen atmosphere. And the way that we were doing that in our small-scale things was in our little oven in the shop down here, but in this case we couldn't imagine it being stable and we didn't want to risk this whole thing. It cost us seven thousand bucks for the source I think, and that was the highest piece of money that was in the whole experiment. I don't think, in terms of experiments today, this is considered a very significant expenditure — But anyway, I got the help of my old friend who actually worked for me doing Rad Lay days, Fred Rosenburg, who was the head of the tube shop at MIT in the old Building 20. And amusingly, he asked that I not bring any counters and things because the other people in the shop would be concerned, and they were sort of — what do you call it? — gun shy about radiation. And so I didn't, but I had carefully put this thing, I had an iron box made machined out inside so that the iron disc would be lying below the level of the break in the box where the lid and the bottom were bolted together, and then it had holes drilled to allow the gas, the hydrogen gas, to flow through. And on the outside of that box the counter showed, I don't know, 50 — what is it? MR per hour or something. And we got 3 feet away from it and it's down to the radiation level that nobody would think about.
So we took it down there and he did this diffusion for us and I thanked him in the letter that we finally wrote in the publication, and he got a feedback from that because it turned out the health physics people at MIT read the Physical Review Letters and they said, questioned him, “When did you do that?” and “You didn't clear it with us or anything.” And so he called me to say he had trouble from this. How much got out of that, well what I thought he meant was how much cobalt-57, which was the dangerous part, because the initial decay is much more energetic than the one we were using. The one we were using this only happens in 10 percent of the cases, but the high-energy 120 keV kilovolt] which goes through the iron and everything, it was what cobalt-57 really existed for in the — what do you call it? — nuclear medicine trade, because it was used as a calibration for nuclear medicine detectors and so forth. So when he said that I thought he meant that how much came, got out into the room of the actual activity. But what it turned out he meant was how much was the gamma-ray intensity. But I didn't think anything got of the box. I was a little nervous that it might though, because in this high-temperature oven it would evaporate.
Pound:So anyway, I guess that all got —
Rigden:All right. Well, back to the experiments. You got — this now your source.
Yeah. That was the source, and that was mounted on a transducer that vibrated it by enough so that the Doppler shift due to the vibration would carry the resonance from one side to the other side of the absorber line which was in an enriched iron foil at the other end of our 75-foot tower. Now we had to do something to allow this 14-kV gamma ray that was the basis of this Mossbauer resonance to get from one end of the tower to the other, although we couldn't do anything at that time about the inverse square law. We were just 75 feet away. It's considerably less strong than it is at the source. But it also would have been absorbed in 3 feet of air, so we couldn't send it through an air column. So we installed a Mylar, and originally it was only polyethylene but later it became a Mylar cylinder — a bag as we called it — which was inflated with helium. Now we had a continuous flow of helium from the bottom to the top with windows allowing the gamma rays in the tower so that then the absorber was at the bottom. And of course every few days we would reverse it so that the source was at the bottom and the absorber at the top. But we installed as well as these two main components, we installed an absorber with its own — I'm sorry, a detector — with its own — these were, by the way, sodium iodide scintillation detectors, which are not very good for this low energy.
We had absorbed such a detector nearby the source so that this modulation effect, if it were the waveform of the modulation were to change it would show up in the data on this nearby thing and be extractable from the data of the main run because it would effect the two the same way. And that was one control that we did for trying to control the systematic error, and the other one was the inversion. And I always said that we looked at that when both directions and said the effect would be doubled that way but also would be demonstrated to be having — that the only thing we would change was the direction. And that made it an experiment as compared with an observation. I always said the astronomers could only make observations of what came from the sun, and they couldn't turn it on and off, whereas in effect we could more than turn this on and off; we could invert it. Whereas the Brits did not do that, the people from Harwell who gave their report in January. You asked why did Viki Weisskopf do what he did about that. He thought it was improper to let them have a post-deadline paper that was connected with the one that had been an invited paper on Saturday, so he moved that post-deadline into the same session that I was in.
Rigden:And did they come after you?
Rigden:Okay. What turned your thinking onto the temperature effect? That was sort of a subtle thing, wasn't it?
It was. And what I reported in January was the data was coming in, and initially it started to look as if we were seeing what we were hoping to see, but that it was unstable. It wasn't consistent each time; we inverted and so forth. We got the right change of sign but we didn't get the right value of what we mean expected this value. And the data fluctuated all over. In fact on the Monday morning — we started taking data on Sunday of that week. I had a telephone call from Schiffer on Monday. But Monday morning I had gone over to Harvard Coop to buy an electric blanket which I wanted to keep the apparatus in the penthouse because that penthouse was unheated and suffered the New England climate going up and down day after day. And I thought — I didn't think anything about the Mossbauer effect being having anything fundamental to do with the temperature, but I thought there would be thermal expansion that I didn't to have producing Doppler effects in the apparatus. So I got this electric blanket. I had trouble convincing the salesman at the Harvard Coop that I knew how they worked. [laughs] He said, “People buy them for the wrong reasons.
The thermostatic control of an electric blanket is controlled by the room temperature, not by the blanket temperature. If the room temperature is low it turns it on more” and so forth. But anyway, that was silly because it turned out that after we started pursuing, when we came back from New York, we started trying to put various tests of why it was giving such unstable data. There was some idea that we didn't know how to make stable electronics as compared with the Harwell people. But I didn't think that was true because I had great confidence in Glen's abilities in that respect. And I had some of my own at the same time. But in any case, about two weeks later we had done a number of tests — One of the things we first did was I thought, “Maybe the temperature affects this ceramic transducer” we were using to produce the differentiation of the line shift. And so I had been very proud about having obtained that ceramic transducer, because we tried to make some locally.
There was an outfit that made ferroelectric devices of this brand, and I put in an order for them and I kept calling them and said, “Where is it?” and “How is it?” and they said, “Well, the one we tried, when we put it in the oven it cracked.” So this went on and on, and it turned out they had made seven to start with, and every one of them broke when they heat treated it. So I went back to Ted Hunt, my acoustics colleague in the Division of Applied Science, and asked him — and he called up a former associate of his that he had known very well during the war years because he ran the underwater sound lab, who was at Clevite Brush Development Company in Cleveland. And he said he'd give a look. He thought he might have something like that in his shelf. And so he found this and sent it to me very kindly. So that's what we were using for the modulation in a very neat way. It's a silver-plated ceramic cylinder with ferroelectric material, so you put an ac potential on its walls and it vibrates in length and by just the amount we needed. So I took that out and put in a magnetic gadget, moving coil device, and it didn't make anything any better. And then we tried to see whether the Earth's magnetic field or other magnetic fields were doing anything, wound the coil around the thing and we would turn it on. Now it took quite a little while to see whether something had an effect because you had to collect data enough to get the statistics for it. And at first it didn't look as if it did anything, but in the longer, in longer times it seemed as if it finally was doing something, so maybe there was something in that after all. But the real thing that happened was that the coil was heating the thing. But I didn't think of that at the time.
So what happened next was when I was sitting in the upper level experimental lab which I was running as my teaching duty at the same time, where also the control system for our experiment was at the base of the tower, or the midpoint of the tower. And this student came and asked something about what I was doing and I told him about this Mossbauer effect and I said that the fluctuations, thermal fluctuations of the nucleus in the solid were at such high frequencies mainly because of the nature of the phonon wave that they averaged out during the time of emission of the gamma ray, because these gamma rays were 10-7 seconds long and these frequencies were typically 1013. So I said, “but of course the second order doesn't go away.” So then I quickly wrote down on a piece of paper an estimate of the mean squared atomic velocity in thermal vibrations compared to C2 and found the fraction to be about 10-13. So I realized that one degree of temperature would have exactly that as much difference. So that evening I went home for supper and picked up an old coffee can, came in and made a little cryostat out of it in the evening in the machine shop where we could make a test of the temperature effect. Because we could put liquid nitrogen and dry ice and things like that to vary the temperature (?). And sure enough, there the shift fit specific heat curve of a Debye function over the solid quite nicely. So then we sent that off and published that in the middle of March — well I guess we sent it off about the 1st of March.
Then we discovered — The Harwell group had this letter from B. D. Josephson which suggested to them that there should be a temperature effect, and that was a few weeks later. Our letter was already in press. And Josephson was an undergraduate at Cambridge University. Harwell, uh, Walter Marshall told me that he tried to — that's the old story. He tried to call this person called Josephson at Cambridge, Trinity College and the porter answered the telephone and said, “Oh, that's an undergraduate. We don't take telephone calls for our undergraduates.” And so they said, “Well, this is the Atomic Energy Research establishment calling and it's a very important issue,” so they finally did get to talk to him. And then they went and made a measurement, but unhappily they made their measurement with the same apparatus they did their redshift test, and they came out within a factor of only half as big a shift as they expected between the nitrogen temperature and room temperature. They expected the shift to be 2 times 10-13 I think, and they found just one, but they said that was okay. But then I sent Cranshaw a telegram to say the correct number should be 4, which is what we get, because – “Your number calculated must be wrong.” And that of course exposed the fact that their apparatus really wasn't capable of measuring this gravitational redshift.
Rigden:Okay. You just said that the group in England really were not able to measure it because —
Pound:I sent them a telegram, and later I got, when I visited Oxford Brebis Bleaney had a dinner — well, a luncheon — in which he got Walter Marshall to come because — we've got together again, and Walter was telling me that he was really quite annoyed with his colleagues who in the first place had invoked him into helping in the experiment though he was the head of the theoretical department and on the original iron-57. But in the second case they came to him with a question about this letter from Josephson, could this be so, and he looked at it and said, “Oh yeah, it could be,” and then he did a number calculated on the back of an envelope, and that's the number they were going to publish. And Walter said they never checked it themselves. And he was embarrassed by the fact that he made that factor of 2 error. And so —
Rigden:Did they ever withdraw their —?
Pound:They didn’t publish that but did publish Josephson’s article on the effect of temperature.
Rigden:They never published. Okay.
Pound:They never withdrew their original one though, in which they did publish the thing that they reported at that January APS meeting. And Viki had suggested that if I wanted to get in on the publications, saying he knew that they had, that they had submitted the paper to Phys. Rev. Letters. And he suggested if I wanted to be along with the earliest publications I should have a paper in as well.
Rigden:Did that compromise priority at all do you think?
Pound:I don't know quite what you mean by compromising.
Rigden:Well, did people — did anyone —?
Pound:Cite them as the number one?
Pound:Not many. I usually get cited. Pound and Rebka usually get cited as the ones who did this experiment, although some people say Mossbauer did it. But a few places that only Cranshaw and company, Schiff or Cranshaw get mentioned, because one such case is the first book of Stephen Hawking who describes the redshift had first and finally been measured determined by the group at Harwell and never mentioned us then. But when Hawking was here a year or so ago, a couple years ago — he's a remarkable fellow B he came in a special van in which he could get his chair in and out, or his assistant, his now wife, came with him. And I went over to say hello because I had known him from when he came here in — what was it? '67 or something like that B and I told him who I was and so forth, and I said, “You remember?” And he sat there with his computer and typed out — I had to wait around for 5 minutes or so to hear his response. And he said, “Of course I know you. We consider you with having proven that the relativity was correct” and so forth, and he was very generous in this little conversation.
Rigden:Let me ask you a question. It may be — I don't know how you feel personally, but you know sometime in the late sixties, or in the sixties as I recall, there were people talking about you getting a Nobel Prize for this. Did you ever think of that?
Pound:Well you know, when you said, “Did you ever think of it?” I never supposed that — I know that having that kind of competition and having so many people involved in this and that means you don't get cited. Actually when you come down to it, I have said that I won a prize once that had some money attached to it, namely in 1948 I won the B. J. Thompson Memorial Award of the IRE, Institute for Radio Engineers, and I had a hundred dollar check. But that's the only prize I've ever won that had any money. And except that when I gave the Lauterbur lecture to the International Society for Magnetic Resonance in Medicine, there was a, a stipend came with that which is the biggest prize I've ever got. So anyway, as I say, I know that a colleague who has a Nobel Prize himself, namely Sheldon Glashow, told me he wanted to nominate, put my name in as a nomination for a joint prize with Irwin Shapiro [spelling?] for our contributions to experimental relativity. That's the last I ever heard of it, but he did do that.
Rigden:But you surely have been nominated earlier. Are you aware of it?
Rigden:You're not. Well, I know in my conversations over the years I know on a few occasions when you talk about the Prize and so forth, people have mentioned that Pound should have gotten a Prize for the redshift experiment.
Pound:Well, especially it's awful — I don't really like prizes as such. They seem to change people.
Pound:Of course you know I lived through both the fact that this was essentially bypassed by the fact that Mossbauer got a prize for his thing, but I don't think his thing got much notice before we started this high-resolution stuff. And that's what — it was the iron that really turned into the tool of all the condensed matter physics and chemists and such people. And 90-odd percent of Mossbauer's spectroscopy went on to that. And its role in nuclear physics was nil.
Rigden:Yeah. Well, are there other — anything else you want to say about this wonderful experiment that will live forever?
Well, one thing is that it's always cited as this 10 percent experiment of Pound and Rebka but that we went on for four years later, three years more, and it was a comparable amount or more effort put into trying to improve. And then after that, with the help of Joe Snyder, we got a 1 percent experiment, probably a little better than 1 percent. I was fairly generous in attributing the uncertainties. But then of course I have continued with other students and such to pursue the possibility of developing a light pipe to overcome the inverse square law. So that the original experiment is independent of height because the intensity of the radiation falls at the inverse square law, and the uncertainty in being able to measure it improves because the shift is greater. And these two things cancel exactly so it means that the statistical data is independent of the height. So you could do it in the height of a tabletop in principle, but not in practice because there's the issue of systematic error.
So if you could make a system that could avoid the inverse square law then you can use a much taller system, and I looked into using locally the Prudential Tower and went to New York and studied the Empire State Building and decided that like Edwin H. Hall, our colleague of 1902 who used this tower here, that there were advantages in having the results of your colleagues in the laboratory at hand that over-weighed some of the opportunities of having a larger place. Because he had looked into using the Washington Monument as a basis for his tests of whether objects fall south, move south when they drop. And I had the same concept of the advantage of the laboratory. The real thing that put me off about the Empire State Building was that all the high-energy radio and TV emissions for the New York area go from the top of that building and the electromagnetic background must be something pretty fierce. I didn't think that it would be much fun to try to run sensitive detectors in such an environment.
Rigden:Let me just ask one more question. If you had named that, if you had titled your paper something like “Verification of Einstein's Redshift,” it would have attracted more attention than “The Weight of a Photon.” Why did you name it that?
Pound:I named it “The Apparent Weight of Photons” in the original paper, and I got flack from Jerrold Zacharias when I gave a talk at MIT because Jerrold came — he was my boss during World War II — and he said he had made a reputation over trying to develop atomic clocks sufficiently well to be able to do the redshift experiment, and that's one of the things that put it in my mind because he talked about it off and on. He came up with this idea of the fountain kind of atomic clock basis and he, but he was thinking of measuring between the top and bottom of mountains in Switzerland for example. But he hadn't got that far. And he said, “You know that was a great experiment, but it was a terrible title. Why did you use such a title? You know it isn't that, because nothing happens to the photon. It's only that the timescales of the two ends are different.” And I said, “Yes, that may be, but I can't prove it by my experiment because we only measure that the effect is the same as it would be on anything else falling in that length of time.” I think he may have partly accepted my argument. And I also had flack from Lev Okum, a Russian.
Pound:No. A more, a man that's still relativist and — oh, he writes on — he dislikes the idea of implying that something happens to the photon also. I'll think of that name eventually. But anyway, I thought it was less pretentious to talk about that, to talk about it this way. Because it doesn't overplay what we actually operationally could test.
Rigden:Later, in fact it was around — I think 1980s, early '80s when you did your little experiment with heating yourself with microwaves?
Well actually I never really got to doing an experiment on myself. That thing over there in that box in the bottom is a 500-watt 5300 MHZ backward wave oscillator which once had a classification that should not have allowed it out, but they gave it to me from Raytheon because a man named John Osachuk was an officer there and he's one of the strongest exponents of opposition to all the business about the dangers of electromagnetic fields. That's partly because Raytheon owns the company that builds — well, they started the building of microwave ovens and so forth. Of course they got all kinds of flack and lawsuits and things about the dangers and the hazards and the troubles produced by things like that. So in that general area of science if you call it, he's one of the people I had interests with, and the other person of significance was — what's her name? Ellen R. Adair. And Ellen R. Adair is the wife of Bob Adair of Yale, and she is an experimental psychologist and she worked with — what is it called? The J. B. Johnson? No, the foundation which is associated with Yale University Medical School in which they are concerned with the effects — They had a big project there for measuring the effect of infrared radiation on people and so forth. And she had an oven, a microwave thing in which she was studying the effect of microwaves on squirrel monkeys, the behavior of squirrel monkeys. And she was very excited when I published this paper in Science in 1980 on using it for heating people, because she had never found any significant impairment or any problem with her monkeys that — Well, she in fact has done some very worthwhile experiments under the auspices of the Air Force, I think it was an Air Force base she went to in Texas, and she got written up in the New York Times a couple of times in the last year or so about having — She finally got around to doing experiments with people.
I never got around to doing anything. I was going to build a demonstration facility here, and I got approval of the IRB, the Institutional Review Board, for carrying out experiments on human subjects, with some conditions. Among the conditions were that I could only use subjects who were knowledgeable enough about all the controversies to know what kind of risk they were taking. And I knew they weren't really taking any risk, but that's all right. Of course there was a large group of — many people really felt that the evidence was strong that cataracts of the eye were strongly produced by the effect of microwaves, but the man who had originally done that said, “Look. If I had radiated anything but the eyeball with that, people would have fried,” because he said he was using a tremendously high level compared with anything anybody would think of being exposed to just for this purpose. And there was a man in Alabama, the University of Alabama I believe it is, where they had a primate center, and he wrote me one time that he was having trouble getting Science magazine to publish this article which he had written describe these thorough experiments he had done with primates, monkeys too, in which he had them go suck on a tube from which they could be fed honey, and every time they'd do this the 3-centimeter wave microwave source would blast them in the face. And he had a team of ophthalmologists and clinical psychologists, all kinds of medical people that analyzed them, after doing this for several months on these beasts, to see whether they had shown any problem with their eyes.
Pound:So, and this of course, the people that look into these questions always doubt their validity because they know that the project in this case was supported by the U.S. Navy and it was in the interest of the U.S. Navy because they were under suit from former radar operators from ships that had 3-centimeter radar who were claiming that they had damages that had been caused by their employment. And I gave a talk, as I mentioned the other day, to this group that Heinz Barschall chaired at the University of Wisconsin. I was there actually to give the lectures on, in the physics department there is an endowed lectureship which is named for Julian Mack used a spectroscopist to compose the tables of nuclear isotope tables? X-ray spectroscopist? What was his name? Anyway, they have that lecture series that I was to give, and Heinz got me to give this talk, and he told me that he was about — he had been attempting to organize a conference on the effects of electromagnetic fields and there was one person whose name I won't mention who is a dominant antagonist in this area — sort of the biggest known name attacking people — he wrote and was going to get him to come and this man replied that he had seen that Pound was on the list of invitees and anyplace that he was going to be he wouldn't think of going.
Pound:And that's how Barschall introduced me to my talk in Wisconsin.
Rigden:So that experiment, really you never did fulfill that.
Pound:I never carried it out. I had a little shed out here which —
Rigden:Is that the old little red shed?
Pound:No, it was another. There were three sheds out there beside what was then named “Research Laboratory of Physics,” later renamed the Lyman Laboratory of Physics.
Rigden:One of the sheds you did the NMR experiment.
Pound:Yes, that's right, the big one. The big one. And that's going to come down. It was supposed to come down last December. I was asked by one of the people in the lab here who was doing some of the historical things, he wanted to know about the history of that and so forth, and then he asked if I had qualms about, sensed loss in its coming down, and I said not really, because it had changed its use so much and been fancied up and wasn't at all like what it was then and I said I would feel much more loss in the disappearance of the tower situation in Jefferson — which is gone too.
Rigden:That's gone, yes. You said that.
Pound:The tower is still a separate masonry structure there, but the top penthouse and the attic space through which we had to carry all that junk back and forth and down to the basement Sabine reverberation chamber, there was a lot of physical effort that had to go into getting that experiment done. They are now modifying that space above the fourth floor in Jefferson into office space for more theorists and so they, they called a meeting a few months ago to see whether there was anything of historical significance still lying around up there. And there was one thing that was there which they have collected and Andy Strominger, who is actually a — what do you call it?
Pound:A string theorist. No, he is the head of the theoretical people, but had got all that modification done on the fourth floor, people somewhat cynically call it the Taj Mahal the way they modified the fourth floor at Jefferson, but he wanted to have this thing preserved as part of the art work in memory of this experimental thing in that new space they are going to build. And what the thing that was found and I knew was there actually was one of the two big proportional counters that Ron Drever designed when he was here that year in 1960. 1961, wasn't it?
Pound:By the way, you know the book you sent me that had a picture of me and the experiment or something?
Pound:On the other page it had the gravity wave detector from Cal Tech.
Pound:In the one picture — I showed this to Ron Drever, and he was a bit concerned over the fact that he was involved in both of those pictures. Because that thing at Cal Tech was his, and within that picture on my page of my experiment was his, quite significantly observable was his proportional counter which he built for our project.
Rigden:Okay. And I wrote the captions on those things, so — Well, let's move on. We'll probably have a little more — In fact, we're almost done but we'll keep on going here. All right. Bob, you said you wanted to say one more thing in the experimental vein.
Pound:Well, on the issue of being able to test the effect of microwaves as a heating source for people. I made applications for a patent on the idea and that got canned by a patent examiner who took an illegal position of judging it as being medically dangerous. And that was not his role. That had nothing to do with it. But we were not successful in fighting him that way, and I decided it wasn't worth the effort because there was so much, so many people were gun shy of the idea that I knew it wouldn't ever go anywhere. But then the other thing was, that I thought I could get some support from the DOE because they in fact had participated in some conferences they set up, but then they — there was one conference at Yale with Ellen R. Adair and company, and it was the, one of the divisions of the DOE on environmental safety or something like that, and they behaved in the beginning as if they might be interested in seeing some support in this thing. But when I got around to talking to them directly about that possibility they thought that they would have to put so many conditions on how it was done that they wouldn't do it. But then they got me involved with the new sources of energy kind of group at the DOE. What was his name? A Polish name that chaired that division. And he encouraged me to submit a proposal and I submitted a proposal to get some funding to do this thing where I thought you could have some people go sit at the desk and read with the surroundings at 40 degrees but feel happy because they were in this radiation field. And they had to send that out for review and they sent it to ten reviewers, and the list of their responses was that some were extremely enthusiastic. A couple were moderately, but I think it was three that were very negative, in particular the most negative was this person I mentioned otherwise, saying he was shocked that a major university with a reputation would tolerate anybody making proposals like this and so forth. And so — And it sounds to him as if he would have to make a tutorial report here to explain what electromagnetic fields are all about to this man. And he didn't — Perhaps he didn't know that I had taught the course for many years in intermediate electricity and magnetism, but never mind. So anyway —
Pound:That's what happened to that, and that's why these things just sit here, and that's the power supply for that klystron, that backward wave klystron, and my students — I had some wonderful students back in the seventies and eighties who put this whole system together. And I never got to use it really.
Rigden:One of your long-time students — who I got to know — was Vetterling, Bill.
Pound:Oh yes, Bill.
Rigden:Is he still at Raytheon?
Rigden:Okay. All right. Well listen —
Pound:No, not Raytheon, Polaroid.
Rigden:Polaroid. Yes, that's right.
Pound:Polaroid. And he's the fair-haired boy there, because the one thing that they want to push of their own now is new technology for printing in digital domain, and he got some fancy prizes from them over the last couple years for the development of their fast-printing high-quality thing that they are going to peddle to the Ritz camera types and so forth.
Rigden:Very good. Bill is a nice guy.
Pound:And he's a great teacher. I've talked to — well, I was hoping that they might bring him back to the division here.
Rigden:Yeah. Okay. This is the end of the tape now. Okay. I would like now — I gave you an outline yesterday.
Rigden:I'd like to sort of talk to you about your life as a professor, and I'd like to ask you about how you maintained a balance between your various responsibilities, most specifically between your research and your teaching.
Well, that's — I always have said that one of the great things about being in this institution is the quality and interests of the graduate students in being in continuous contact with this developing young people, remarkable for — and you mentioned one just now who was such a person. And of course I started with — my first student of significance, that I was solely responsible for but never really completely because there was always colleagues in the background, was George Watkins, who is now a member of the National Academy and so forth. But he came to me in '49 I think when I was first a faculty member, and in those days the students I had were mostly veterans from World War II, as he was. He had been in the Navy during the war. And then the next student was the one named Christopher Dean, and he followed up on the Dehmelt and Kruger studies of chlorine in his thesis work and pure quadrupole resonance, and we developed and continued to develop for quite a time when he went to the University of Pittsburgh the super-generative kind of NMR detector which I was aware about the behavior of super regenerative devices from my ham radio days, because that's what we used for UHF kind of reception in those days.
It was a very crummy kind of thing, but it turned out to have some qualities that also made it into a pretty good EQR detector. And so far in my — and my teaching as an assignment was I began in — I said the other day that I had given a special course of my own design as a junior fellow. That's not allowed in — well, it was, in those days there was a taxation issue as to whether people could be asked to do things for the university as junior fellows because the junior fellowship was then not taxable. But now it is taxed like every other fellowship and so forth, so it would be different now. But I gave that course with, oh I don't know, eighteen or so students, including Dave Middleton who was a specialist in the theory of noise. He had worked during World War II with Ben Van Vleck on that subject and so forth.
But when I first started teaching as a member of our physics department I got assigned initially a course called “Physics 10.” And the theory of Physics 10 was that it was a one-semester course that brought the students who had studied Physics 1, which was sort of a non-calculus-based physics mostly for premeds up to the level of Physics 11, so 1 + 10 is 11. It was an impossible thing actually, because in principle you supposed that these were students who had developed an interest and wanted to learn, but actually they were students who wanted to satisfy some requirements that required them to have the equivalent of 11. And then they were doing this struggle in the least painful way they could. So that was my first teaching assignment, and I say it was impossible because you had to cover the whole of elementary physics in one semester at the level that was higher than anything they'd [had]. And you soon learned they hadn't learned much of anything from Physics 1 yet, so it didn’t really work. Then I took over the teaching of the intermediate level of electricity and magnetism, which was 131 in our system, and I taught that. I have a book here with many, many names in it of people that I still meet when I go out to various places who say they were in your course and so forth.
Rigden:Is that the course Purcell eventually took over his EMM book came out of?
Pound:No, he didn't take that one over. His EMM book was aimed at the introductory level, which was 11B, and it became 12B.
Rigden:That's right. That was the Berkeley course.
Pound:And then it became 13B. It was always regarded here as a bit too hard for our first year students.
Rigden:Yeah. Okay, you go ahead, I'm sorry.
Pound:And I used his book when I taught. I did teach 11 and then 12 — or then 13, which 13 was the course of the same sort of curriculum but which was designed to take advantage of advanced placement students that had had calculus and things since high school and so forth, and I taught the electricity side of that, and I had advantage of the manuscript from Ed's book before it was printed. And then during the time I was doing the redshift experiment I had been assigned to give 12A, which was the mechanics course. Is that right?
Rigden:I think that's right, from things I've read about you.
Pound:Yeah. That was the first time I had taught that course, and there were 230-odd or something like that number of students in the course, and that was in the spring of the time that I was in trouble about what the instability was. And I guess I wrote it in that article about the night that I had come in in order to make my notes for the 9 o'clock course the next morning, and at 12:30 the telephone rang and it was the Harvard Police.
Rigden:Yes, go ahead.
Pound:Who told me that my wife had been trying to get in touch with me because she said there had been an explosion in the oil furnace downstairs. And so I rushed home and the oil burner man was there working on it, and he couldn't figure out why, but he thought he had fixed it and put it together and I came back to continue what I was doing, and it was by then 1:30 in the morning. And then shortly after I got back Betty called me again and said it had exploded again. So I went back and the oil man was there again and he said, “Do you have to work this time of day?” He said, “I'm a night man for the oil company.” I said I have to work all times of day. And so then he suggested that well, he didn't know quite what it was, but it was a very cold night and you couldn't be without the furnace, so he said it would get it running and let it stay running and if it got to satisfy the thermostat — and it has a high-temperature shutoff, because that house had radiant heat in which the floors and the ceilings and so forth were heated. It was a contemporary house designed by a contemporary architect named Carl Koch. And so he said I should listen for it to shut down and if it did then I should turn the switch off so it wouldn't try to start again. Well, I went to bed but fell asleep. And at 7:30 in the morning it went blam again, so it was lucky because I could get up and go and make it to my class.
Rigden:Do you feel that your teaching and research were comfortable partners, or was there tension between them?
Pound:No, I never sensed any particular tension between them. No, I didn't. Because — well, I think I learned always from teaching things that were significant in my knowing of things. The second course I gave for example was electron physics, which was a graduate level course, 231, and I picked up the syllabus for that. Purcell had given that course the year before, and before him it was E. L. Chaffee that had given it, called Physical Electronics or something. But there I learned about things like magnetic lenses and the reason why betatrons had to have the right kind of magnetic field shape and not fall off more rapidly, the 1 over R, whatever it is, and the fact that it made the vertical and horizontal oscillations at certain frequencies. I got through a lot of things there that were quite useful to know. And I had quite a group of students. Do you know the name of George Benedick for example?
Pound:Well, George was a student in that course as I always remembered, and George was rather pushy in the sense that he didn't want me to get away with not explaining things completely or something. But I of course have been friends with him ever since.
Rigden:You have been privileged to work in a very special environment. Let me just tell you a little story. Your former colleague, Schwinger, I spent time with him in UCLA. He told me he would never have dreamed the difference between Harvard and UCLA. He said, “At Harvard I had four good students a year. At UCLA I have four good students a decade.”
Pound:Yeah. I can believe that. Well, I oversaw Julian Schwinger's decision to depart from Harvard, and I was department chairman you see, and so I am looked upon as the one that lost Julian. And the thing was, that he had this longstanding friendship with Saxon [spelling?] who had moved up by that time to be the president of California University System.
Pound:But he had been trying to get Julian to come to the UCLA physics department while Dave was there, but Julian had become concerned about physical health being dominant in determining mental health in the long run. So, unknown to his friends here — except he told me — he and Clarice, his wife, had hired the YWCA swimming pool for once a week in Cambridge and they would spend the whole morning at the swimming pool. But he said he could go to California and have his own swimming pool. And then this close friend of mine called Asim Ylilig who was a Turkish fellow who had been an engineer and had become graduate student of Julian's after having actually also held a professorship at the University of New Hampshire. He told me that Julian, he went to Julian and asked him if he would teach him physics, what kinds of physics he meant, and he said he made a compact with Julian that if he would teach him physics Asim would teach him tennis. And so Asim was a world class tennis player actually, and he got me back to playing tennis and I belonged to the Badminton and Tennis club in Boston, because he was the one that got me there. But he had been invited to the Longwood Cricket Club when he came here as a student because he had got a doctorate in engineering from Yale already but he wanted — he claimed it was hearing me give a talk at New Hampshire where he had this professorship that got him concerned and interested in physics. And so he came and applied to get a Ph.D. in physics, but under Schwinger. And he had been in Turkey a member of the Turkish Davis Cup, was it, Davis Cup tennis team and was taught tennis by, his tennis was created by that famous German, prewar German tennis player.
Rigden:Well, actually Julian Schwinger told me about that.
Pound:Oh did he?
Rigden:Yeah, yeah. Let me shift now again to — we're sitting here in 2003 and this will be the last topic. Your life in physics started, well, started with the Rad Lab, and so it's a good, an amazing period in the history of physics that you have been one of the principal —
Pound:Well in a sense it even started in college, because I always remember having to give a talk about analog computers back as an undergraduate, and the research apparatus I had to build.
Rigden:I have two questions. The first one is, as you think about all the physicists you have known and seen come through Harvard and whatever, how would you — would you care to comment on any of them? In terms of your sense of the contribution they made and —?
Pound:Mmm, well that's a pretty broad and —
Rigden:Yes, it's perhaps too broad, but I just thought there may be a couple that stand out in your mind or —
Pound:Well, I hadn't thought about it that way. Of course Purcell, having been such a close friend with whom I shared a lot of things and most of the time when he was doing things that I would hear about it more or less directly from Ed. Of course the other person that I had a great attraction to was Henry Torrey, the other member of our team, because I always felt that he had really been very helpful in turning me back into being a physicist, because really what we were doing at MIT Radiation Lab was engineering, was communications engineering basically. And I have a feeling that Henry, he was always very supportive, and you know there's that picture of the three of us. The other person I was trying to remember was Desmond Kuper, JBH Kuper, do you remember him?
Pound:K-u-p-e-r. He was the editor of RSI for many years.
Pound:Those two, and I have my little communications thing which was based on my stabilized oscillator, and Henry always said he was embarrassed to be in that picture because he had nothing to do with that, and neither did Kuper. That was entirely my own thing. And I don't know if I told you about the fact that Louis Ridenour, who came back from the Office of the Secretary of War came and wanted to learn enough about microwaves to set up another group to develop that thing into a communications system. And he did. He said he got the dregs from lab, because at that time it was late.
Rigden:Well let me ask one name. Did you know, did you ever meet Bohr?
Pound:Yes, I did.
Rigden:What did you think of Bohr?
Pound:Oh, I thought he was a very fine man, and I went to Copenhagen in the summer of '51 and I knew Bohr's son Aage rather well, and he suggested that I come. I was in England as I told on this Fulbright thing, and he suggested at the time to come to Copenhagen might be one — Bohr was running a reunion at the Institute for those people who had been fellows there over the years, and he thought I should come then, because then I could participate and listen in on that. And people like Bethe — And in fact the person that flew from England and helped us get to the airport and so forth at that time was Hans von Halban, Hans Halban, who had been in Los Alamos during the war. But he was a very close friend, and he had left Germany to go and work with Joliet-Curie in Paris, and when France was falling Joliet-Curie sent Halban and Kowarski with all the collected heavy water to England, and the Germans tried to catch them and sank a cross-channel boat, but it was not the one they were on.
Rigden:The wrong boat, huh?
Pound:Yeah. So Halban — You see one reason I wanted to go to — part of the reason I wanted to go to Copenhagen is that my wife's family are all Danish, and she's very well connected in Denmark. But we got invited then as a result to the reception at Bohr's house. You know, Bohr lived in the Carlsberg Foundation house which is on the grounds of the Carlsberg Brewery. It's the only party I've been to where it ended up with fireworks in the garden at the end.
Rigden:That's nice. All right, let me ask one more question. Not people, but just physics, over the period of your active career from start to now, physics, the culture of physics has changed, the support for physics has changed, the scale of physics has changed. How do you think about it?
Pound:Well, there are aspects of all of that that depress me considerably because I ask myself if I were starting over now would I find myself oriented that way. I don't know what else I would be oriented towards, but I don't find it very attractive to be, to have to deal with the kind of things that people have to deal with nowadays — especially the raising big monies and being parties to big groups in which you have a little piece of the action and so forth.
Rigden:And the degree of specialization is what you're saying, yeah.
Pound:That's right. And when I've given talks I've described the difference between prewar, postwar and now as evidenced by the number of pages published in the Physical Review, and in 1939 one month of the Physical Review contained about 200 and some pages. In 1946, the year of our first letter on NMR it contained 53 I think, for the whole month. That was two issues jointly put together. But then by the year I was writing this up in the 1990s sometime one month of the Physical Review contained 8,000 pages in its — what is its nine or ten versions.
Rigden:Yeah. A, B, C, D.
Pound:Yeah. And the Letters is a separate issue.
Rigden:No, it's a different world.
Pound:And you know, even in 1960 when I gave this talk on the redshift everybody knew — everybody that went to the Physical Society meeting was interested and came to that big auditorium where I gave that invited talk. But nowadays it would be so fractionated — one little thing here, one little thing there. I mean, there will be big crowds at every one of them because there are so many big crowds available.
Rigden:But how do young physicists get enculturated into the discipline? I'll tell you, that January meeting, annual meeting of APS as a very young person, I went to hear the talks of the big players, and I became aware of physics through that meeting. You know, it was one big meeting. That doesn't —
Pound:That's right. Exactly.
Rigden:A young person today has no idea as they look through Phys. Rev. Letters whose papers they should pay attention to because they are important people. They don't know that.
Pound:That's right. I agree. And of course there is so many, so much volume of it that you can't possibly cover anything significant of the totality, whereas back in those days you looked at the whole issue of what's coming out and you knew that everybody was excited by one thing or another thing at a given time. Let's say Charlie Townes describing the possibility of making a maser back in the 1950s, and Charlie has also cited the fact that our experiment called a spin system at negative temperatures or something like that was part of his inspiration for it because he realized from that that stimulated emission was going to be a significant factor. Because that's the first publication which specifically described that, because the inverted system when it was tickled with rf emitted rather than absorbed.
Rigden:What do you think about the relationship between theory and experiment today as opposed to fifty years ago? And you're building new wings for theorists here. Have theorists lost touch with experiment?
Pound:I don't really think so. This man, Andy Strominger whom I mentioned as having overseen that thing, he teaches the course on general relativity in the graduate school and every year he asks me to come and give one of the lectures there on the redshift because he said, “This is where it was done.” And he has on the wall up in that Taj Mahal the number which was the energy shift due to the redshift in that building, taken from my paper. And he had it engraved into the glass of the department office up there.
Rigden:Have you taken a picture of it?
Pound:No. [laughs] He's the one that I mentioned that wanted to collect that counter thing as a part of the artwork of the renovated attic.
Rigden:Bob Pound, this has been a wonderful period. And I want to thank you for myself and for AIP, but before I turn off the tape, is there anything you want to add?
Pound:Well, I thank you for thinking of me in this respect, and it's been a pleasant opp but I'm afraid I have a tendency to over-talk.
Rigden:You've done very well. I don't think you should feel that. And I will tell you, long after you and I are gone, people will be looking at these transcripts and bringing insights into the work you've done and into the period you've been a part of. These are very frequently used results at AIP. So once again thank you, and this tape is almost done so I'm going to turn it off.
Session I | Session II