Oral History Transcript — Robert V. Pound
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Robert Pound; May 22, 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:Let's start. This is John Rigden. It is May the 22, 2003. I am sitting here with Professor Robert V. Pound in his office in Lyman Hall of Physics.
Pound:Lyman Laboratory of Physics.
Rigden:Lyman Laboratory of Physics, and we are on the fourth floor. Professor Pound is ready to talk and I'm ready to start asking questions, so let's begin. By the way, for the purposes of this tape I have known Professor Pound for many years and I will probably call him Bob most of the time, because that is how I think of him, so the informality will probably be apparent. Bob, let's just begin at the early part of your life, in fact the beginning. Where and when were you born?
Pound:I was born in 1919 in Ridgeway, Ontario, which is a few miles on the other side of the Niagara River from Buffalo, in the Niagara Frontier as it's called, near Niagara Falls and all that jazz. In fact my father's father, my father's family, the name family Pound and my father’s mother's family both were United Empire loyalists who came to Canada in the 1780s during the time of the rebellion, and they acquired Crown grants as a result of being, having demonstrated that they had supported the British during the rebellion. In fact I discovered recently the background of my grandmother, whom actually I never knew because she died when she was twenty-six or twenty-eight. They had become homesteaders in North Dakota where she contracted tuberculosis B the called consumption. Her name was Francis Ellsworth — and her ancestor was Francis with an i instead of an e, who was granted the piece of land closest to the Horseshoe Falls in Niagara Falls, including Table Rock. So, unfortunately, he sold it in 1817, but never mind.
Rigden:Okay. So you were born in Canada. How long did you live in Canada?
Pound:We lived in Ridgeway full time until 1923. My father joined the new faculty of Arts & Science at the University of Buffalo across the river in the Department of Mathematics. He started there in 1922 but commuted from our Canadian house in '22. But then they moved the university to the north side of Buffalo, which was too far from the ferry, and so we bought a house on that side of Buffalo and we moved over there for the academic years but we continued to live in Ridgeway during the summer months. It was a fairly long summer from the academic year, so even I had to start school in Ridgeway when I was old enough, but only for a few weeks, until we went back to Buffalo for the winter.
Rigden:So you were about four when you came to the United States.
Pound:I was four when I came there, and I was sixteen when we finally gave up our house in Canada even for summers.
Rigden:When you were a third grader you learned a new word called physics.
Pound:[laughs] You read that.
Rigden:I read that. Was this in any way the beginning of your interest in physics?
Pound:Well, I suppose not — I really didn't know what it was, but my father was an experienced man in physics and he had done his Ph.D. at Toronto in 1912.
Pound:Yes, in 1912, I'm sorry, under J. C. McLennan, who was the best known physicist at Toronto in those days. He became Sir John later, knighted for work in WW I. And my father left there in 1913 to go to Queens University in Kingston where he spent the next five years — four years I guess it was — before he came back to Ridgeway to help his father in a small company that they jointly held called the Ridgeway Milling Company. And he was general manager for the flour mill. But then he decided to go back to academics. Of course the milling business went down the drain pretty much after World War I. It was a big business during World War I, and then they had a number of other facilities, like being a party to the Bertie Township Gas Company, because several of the wells, gas wells, were on property that people of my family had owned. They used to have their board meetings in our living room. And I used to have a nice seal stamp thing that said Bertie Township Gas Company or something. But the gas companies were all taken over by a provincial gas company, consolidated and that sort of disappeared too.
Rigden:How do you spell Bertie Gas?
Pound:B-e-r-t-i-e. That's the name of the township of which Ridgeway was a part. All that's changed now because it's all part of the Fort Erie municipality.
Rigden:All right. While we're still talking about your early interest in physics, or your interests [unintelligible word], Rabi said there were two kinds of physicists — one turned to physics because of troubles with their radio kits, the others turned to physics because of troubles with their God. Were you either of those?
Pound:No, I wouldn't say I was, because I never thought much about going into anything else but physics, although my idea of going into physics never — I never enthused for the academic side at that point, because my father, being an academic, I knew that they didn't get treated very well, and I thought I was going to become something like a research person in a corporation, you know, something like General Radio, Naval Research Lab or some such place. But my experience in college and then particularly after the war changed all that.
Rigden:Did you have any particular experiences in high school that were important in your career and your development as a physicist?
Pound:No, I would say that my experiences were completely self-made in that connection. I became interested in building radios and things when I was about nine or ten and built my first radio, which used the first a.c.-powered vacuum tubes, the 227s, and was built from a circuit in, I think, Popular Mechanics along about 1929. My father helped me in that respect in the sense that he had a large collection of radio parts, because he used to build radios when I was very young. In fact in Ridgeway he had a battery-operated radio that he had built, and I can still remember the family each using a single headphone of his radio to listen to the Prince of Wales dedicating the Peace Bridge a few miles away from Buffalo to Ft. Erie. That was in 1926, and they brought the Prince of Wales over to serve the dedication. My father would drive the old Model T up beside the windows in the study of his in our Ridgeway house and run the leads out to use its storage battery for the filaments of his radios.
Rigden:Now the radio was an AM radio?
Pound:Oh yes, an AM of course.
Rigden:It wasn't a ham radio.
Pound:Oh no. No. That's right. Those radios were battery powered, then I built this a.c. one which just used two vacuum tubes and had a regenerative detector. That had a lot of influence on my postwar involvement in NMR in the sense that the marginal oscillators for which I'm pretty well known were in fact derivatives of regenerative radio detectors.
Rigden:That you did back when you were nine years old.
Pound:Yeah, that's right. And then I went on, when we moved to a different house in Buffalo which was a newly built house and a better than the one we had bought way back in '22. My neighbor was an older boy, four or five, four years older than I, I guess. And his father was the superintendent of lighthouses for the Lake Erie and Lake Ontario, and they had three ships in Buffalo Harbor, the biggest one called the Crocus. And the Crocus was a lighthouse tender, and the lighthouse service was a separate division under the Commerce Department then, not connected with the Coast Guard. The Coast Guard was also under the Commerce Department, but Roscoe House, the superintendent of lighthouses, got the opportunity twice in the summer to use that ship as a sort of cruise ship after they had reset the navigational buoys. They had built quarters for the superintendent, the family who would all go in the early summer, they would go up the lake, up Lake Erie to Cleveland or Detroit and then come back and visit all the lighthouses and the lighthouse keepers along the shore. It's about a two-week cruise. And then later in the summer they would go through the Welland Canal and do the same thing for Lake Ontario. And Bob, as a boy, went along with that, and he got to know the radio operator on the ship. And I remember his name is Steve Gusparovich.
Pound:Yes, Gusparovich. And he operated this long wave ships radio which was running on 500-cycle a.c., and it went buzz-buzz-buzz when they keyed it. And Bob got the idea, or Steve Gusparovich suggested that if he got a ham radio he could actually converse when the ship was out on the lakes. And so he got interested in ham radio, he had also been listening to what they used to call a BCL, broadcast listener, and he would stay up late at night and pick up VK2ME from Australia on the ordinary AM radio and such things. So when we moved there I got involved with him and we started studying the code in order to get a ham license.
Rigden:How old were you?
Pound:When I was twelve.
Rigden:You were twelve. Okay. And did this influence your work in high school science courses?
Pound:In the sense that I found them stupid and trivial, yes. I mean in the sense that I petitioned my — I had a great friendship with the physics teacher. He was physics and chemistry, and he'd let us take the chemistry New York State Regents Exam after the first semester, which was the final exam for the full year, but he said we'd have to go on with the course no matter what happened. And we did that, and then he said he wasn't going to do that in physics though, and I talked him into letting me do that, and I got 99 on the physics exam after the first semester. You know, they asked you how to wire, they used to ask you how to wire a doorbell and stuff like that. It was so trivial as far as I was concerned. I skipped the second term.
Rigden:Well Bob, if you got 99, you had learned a lot of physics. Had you learned that just on your own?
Pound:Yeah. I had been heavily into photography for years and I knew a lot of optics, geometrical optics, because I was also building a telescope, grinding a mirror, learned about the Foucault knife edge test, things like that and so forth. And I knew about three different kinds of eyepieces — Ramsden, Newton, and what's the other one? I forget. So I had done all these things, and so that the physics course was absolutely trivial. The 99 was because of the question I missed, was to do with a question of who saw the apple fall. And I never read much of that stuff, so it was multiple choice and I chose the one, I think I chose Galileo instead of Newton. And ever since I've not been one for saying who did what. I say that's a part of social science and not physics in a sense.
Rigden:Well, we're now sitting here and we're going to try to understand what Bob Pound did as we go on. So okay, you went from high school to the University of Buffalo. Was that choice simply because it was nearby?
Pound:It was relatively economic I should say, because I never thought much about going somewhere else, and in many ways I think if I had known enough about Rochester at that time which was quite, fairly nearby, I might have been inclined, because they had a wonderful physics department then with L. A. Dubridge and Vicky Weisskopf and so forth. But — and they were building a cyclotron with Van Voorhis. But — our university, my father taught in the math department, but he actually taught all the analytical mathematics used by the physicists, so he and then I, knew many of the young people who had gone through as physics students there. There’s a man named Marvin Chodorow for example who is a well known applied physics scientist at Stanford in recent times. He was one of my father’s students.
Rigden:Now you entered Buffalo around '37?
Pound:Yeah. And I had two different scholarships — a New York State scholarship. That year was in fact, this high school I went to called Amherst Central High School, it had been founded in 1932 I think or '30, and ours was the first class that won New York State scholarships. They gave forty New York State scholarships in Erie County. I think the number of New York State scholarships was equal with the number of something or other, representatives from the county to the state legislature. And that was the first year any of them had been won by the Amherst Central High School, but there were six of the forty in that school that year. Previously they were won mostly in Buffalo high schools as, for example, by my oldest sister. And then it also was announced at the graduation that I had been awarded an Erie County Supervisors Scholarship to the University of Buffalo, which was a full tuition. In those days tuition was the only thing you got covered with scholarships, so I had that plus the hundred dollars a year for the two years — it was only two years — I'm sorry, full tuition for two years, and in the last two years, of which I only spent a year and a half, I earned my keep by being a teaching assistant. I was so-called senior assistant.
Rigden:Did you, as you look back, do you think you got a good undergraduate education there?
Pound:It was rather spotty I'd say in a sense. I mean there were some very, very dedicated teaching people, but I would say that, for example, a man that was my brother-in-law came there from Yale in the fall of — sorry — in the summer of 1940, and in the fall of 1940 he taught a course called quantum mechanics, but he was really an experimental nuclear physicist and his quantum mechanics was what he'd learned from [Henry] Marganau at Yale. And I didn't learn much from it. I took that course. And but my actual supervisor, advisor and so forth was a man named L. Grant Hector [spelling?], and L. Grant Hector had been a student of [A.P.] Wills at Columbia. In fact the predecessor to I. I. Rabi. In fact Rabi once told me that he took over Hector's apparatus when he became Wills' graduate student. But then Rabi said the trouble was that he, Rabi, was so smart that he didn't ever use anything. He invented a way of doing what he was to do for his thesis without building anything. So then he said thus he regrets that he never learned any experimental physics as a result. I guess I can't tell you much about Rabi, but —
Rigden:Well, that's a true story. Rabi was I think fundamentally lazy, and if he could not find a simple way of doing something he probably didn't do it, and he kept trying until he did.
Pound:I think he did something about adjusting the susceptibility of the things until it balanced.
Rigden:With water, against a sample.
Pound:Yes. A solution.
Rigden:Yeah. I asked you the question about your undergraduate education because I was setting you up a bit. You have the distinction of being a full professor at Harvard and have an illustrious career and you only have a bachelor's degree. That's your only formal degree.
Pound:And that was in three and a half years instead of four, because I left early when I was offered an opportunity to go into defense activity. I didn't have quite enough credit to graduate, but Hector stirred up a couple of extra semester hours credit for my tutorial work so that I could make the graduation requirement. In the tutorial program, I had been pursuing a project in dielectric susceptibilities that took most of my time for the last two years, building electronic apparatus for example.
Rigden:And you left a half a semester early because of the war work?
Rigden:Okay. Now how was it that a young fellow with a bachelor's degree, how did you get attracted to or how did you get an offer to get into defense work? And where did you go from Buffalo?
Pound:Well, of course what was going on then was that the war was getting intense in Europe and our Selective Service began. I had to register for Selective Service October 16, 1940, and it was clear that our future as going to graduate school and going on in science was very prejudiced by all this. And so when my brother-in-law, Howard Schultz, who became a professor at Yale after the war but had got his Ph.D. at Yale in 1937. He had come down as one of the first people being recruited for MIT Radiation Lab. He was also being recruited at the same time, in competition, to a company called the Submarine Signal Company in Boston, in which my other brother-in-law Harold Hart was the head of the radar department. They had developed a radar department entirely on their own starting in 1930, which was long before anybody else. And H.M. Hart had also been a graduate student at Yale and had worked on his thesis work with a man named L.C. McKeehan, who was into magnetostriction which was used in sonar.
Rigden:How do you spell McKeon?
Pound:I'm not sure. M-c-k I think. And he was a consultant to this Submarine Signal Company. And so Harold spent his summers working for them, and they talked him into coming full time around 1937, and he took over and he gave up his thesis work at Yale. Howard Schultz had done his thesis work at Yale with — what's his name? — Ernest Pollard.
Rigden:Oh, Pollard, yeah.
Pound:With Ernie Pollard. They shared in the building of the first Yale cyclotron. So both my sisters were married to physicists who had also graduated from the University of Buffalo.
Rigden:That company your brother-in-law, involved with radar, what did they use for microwave sources?
Pound:It wasn't microwave B it was actually 50 cm, 600 MHz.
Rigden:It wasn't microwave.
Pound:Well, they were developing it when I came. I came down for an interview in November or December 1940 to see about what this — and that's when I first saw radar running. And Harold built this 50-centimeter radar and it used a Western Electric vacuum tube called the 316. It was called a doorknob tube and that was nominally a 300-volt vacuum tube, but they were hitting it with 2500 volt pulses and making pulse r-b signals. And the people who investigated organizations trying to develop radar at that time wanted to know how come they were the only company that was playing with pulsed radar at that time. And the reason was, they were doing it by pure analogy to their business, which was sonar. And they had been founded during World War I under Fessenden patents, I used to hear — I'm not sure about that — for developing sonar. They were founded, I believe, by MIT people actually. And they were very proud of their economic success because they survived during the big Depression by developing what they called Fathometers and renting them or leasing them to the fishing fleets here in Boston which went out to find fishes. And they thought very lowly of Raytheon, which was a more or less defunct company at the time. The only thing they did then was to build vacuum tubes mostly for ham radio and such.
Rigden:All right. You didn't make it clear. You went from your baccalaureate at Buffalo to defense work where?
Pound:In the Submarine Signal Company.
Rigden:In the Submarine Signal Company. And you were there for how long?
Pound:Well, I started there on February 1st, 1941 and in the summer of '41 — well, at the same time I was living, I shared living with my sister Kathleen and brother-in-law, Howard Schultz, who was then at Radiation Lab, so I was quite aware of that combination of things, and the Submarine Signal Company was closely involved with advice and help from Radiation Lab, although they were actually ahead of Radiation Lab in the beginning. In fact we built a pulsar for the magnetron. Sub sic had been brought into the knowledge of the British magnetron as soon as anybody, because the Navy, they were high on the Navy's list of corporations that were important — because they supplied at least 50% of the sonar to the Navy and they did set up experiments on the U.S.S. Semmes, which was the then sort of sailing test bed for the Navy. The Radiation Lab ended up using it for a radar test bed in later times.
Rigden:Why did you leave and go to the Radiation Lab?
Well, in the summer of '41 after I'd been there six or seven months it became clear that Radiation Lab was going to bypass the whole business. To be in research in a small company like that when there were three of us involved in that program didn't strike me as viable. I saw that the company would end up in production of some kind, engineering, and I wasn't inclined in that direction. But I was sent over to MIT Radiation Lab in what they might call “technology transfer” to get briefed and get experience in some aspects of their radar. So I went over there and spent many weeks. Actually I built the first electrostatically deflected PPI, (Plan Precision Indicator), which is the sweeping kind of radar indicator, and Charles Sherwin was building one which was a magnetic type which is what mostly ended up getting used. This was a group that was headed by Bob Bacher, and a man named Ted Seller was the actual head of that group at the time. So I was in conventional electronics, because that was my big experience from my background. And I could see that if I had hung on for a few more weeks before going to Boston, I probably would have ended up directly at Radiation Lab. So I started petitioning, I started to see if I could make this switch. And I would get in touch with F. Wheeler Loomis, who was the associate director, for personnel particularly, and he finally told me that he'd like to offer me a position but he couldn't because with defense deferment I would have to get a release from the company that had got me deferred from the Selective Service.
So I spent some time, in the fall of 1941, this was before Pearl Harbor, they put the condition that they would give me the release if I would finish the actual model of their 50-centimeter radar that they wanted to have as a demonstration of what they had done. It had been working but it was not fully assembled and so forth. We had a pair of big horns on the roof that were steerable. So in fact I went through that and I did that. Finally I got ill in early March '42. And when I got strong enough to go back I went in to see the vice president, a man named Fay Charles and told him this thing was working and finished and so forth, and finally, they signed my release. So then I was able — So I joined the Radiation Lab the same day that Rabi came — I'm sorry, that Jerrold Zacharias came back from Bell Labs and started the microwave components group. So I became one of his first tools in the microwave components group in March, 1942.
Pound:1942, three months after “Pearl Harbor”.
Pound:So I think of myself [as] having been at Radiation Lab before that, you see, because of this visiting and other close contacts.
Rigden:So you were there almost from the beginning.
Rigden:All right. I'm going to switch this tape, because it's almost done. All right. We just concluded that Bob Pound was at the Radiation Lab at MIT almost from the beginning, and I was going to ask you sort of a cultural question. There were a lot of very well established and rather eminent people at the Radiation Lab, and you came in with a bachelor's degree. Were you treated well?
Pound:Oh yes. I would say I was treated well. Of course I knew that having come from a local environment I didn't have the advantages that some of the people coming from elsewhere economically in the beginning did, because I know that my brother-in-law for example was given a salary plus living expenses so that it almost doubled what he was getting as an instructor in college, but of course instructors didn't do very well in those days.
Rigden:Yeah, that's right.
Pound:It was like $1800 a 9-month year or something.
Rigden:Uh-huh. But you were not treated as a go-for?
Pound:Oh no, no. As a mat — Well, you see I was in Zacharias's group and I was one of his — and within a few weeks I got established as sort of one of his favorite subgroup. I had a subgroup that I organized and although that came along when I was in charge of mixers, but I and a man named Louis Smullin were particularly involved in what they call mixers and duplexers, which was the front end of radars. And we had a major problem, which was, because, in the field when colleagues went out to look at Radiation Lab — developed radars they would find they weren't working well at all because the military had no clue about the fact that crystals could always get burned out even at the first turn-on, and so they were operating tens of db or more below their expected receiving. But you see, they would see local echoes perfectly all right because the inverse fourth power that applies in radar. That meant that you didn't notice the loss particularly on local things but you really needed the sensitivity for remote.
Rigden:Let me ask this. In 1941, '42, when the Rad Lab was getting started, how much was known about getting power around a circuit at microwave frequencies?
Pound:Well, there were people who knew about, say, waveguides but they were mostly academics that had never done anything with them. Page for example at Yale had written some articles describing waveguides. Because I know that my other brother-in-law, Harold Hart, told me that on his oral exam there he was asked a question about that and he doubted it. He had never read Page’s article on waveguides. But the big thing at Rad Lab was that everybody was trained, got to know more about microwave technology, because of the wonderful series of lectures by W. W. Hansen. Bill Hansen came every week up [from] Garden City, Long Island, the Sperry Gyroscope Company, where he was full time and gave these once a week lectures which got annotated, got transcribed. Who did that? I keep forgetting. It was one of his cohorts from Stanford who served as the Boswell for those notes, and I still have copies.
Rigden:It wasn't Packard?
Pound:No, no, no. Packard was a graduate student after the war and he only got there late. No, no, this was a — I can see him but I can't remember his name. Names are harder to get as you go along.
Rigden:But things like the Magic T and various components that went into a microwave system, were those invented at the Rad Lab?
Pound:Well, the Magic T is an example of a disputable issue, because Bob Dicke was the one that really realized the full properties of the Magic T if it were properly matched to a system so that all four arms were equivalent. However, there was a patent issue that came up about that. And Dicke had a patent application from Radiation Lab for it, and there was a man — now another name I've forgotten — at the Bell Labs, who had written a book on microwave hybrid circuits. Not a book — I'm sorry, a memorandum for file is what they call it at Bell Labs, and we had access to much. All that stuff came in through our documents office. And this was — and hybrid circuits were the low frequency equivalent to what became a Magic T. And he was discussing how to make them in microwaves correctness and waveguides for example. And it was what we ended up calling a rat ring, a rat race with four arms going into a ring of waveguide, and if you put them at quarter wave spacing and halfway and so forth you got the exact same behavior as you got with a Magic T, although that was before there was a Magic T. But then that paper went on to describe that you could put a waveguide on the side which you called a series junction or on the broad side of the waveguide, or the narrow side and call it the equivalent of a parallel junction. But the difference would be that you'd moved a quarter wavelength to go from one to the other, because then the phase issues were the same. But then he had a picture in his report showing that you could even put two of them in the same place. But that picture, which was a Magic T by everyone's understanding later, was a picture of what you might have as a pair of junctions on the ring — not a recognition that in itself it was just what he was looking for. And yet that picture won the patent issue, so he got the patent on, Bell Labs got the patent on that thing.
Rigden:One more question in this same vein. To what extent were you guided by any theory that say Julian Schwinger was doing?
Pound:Very little, because in my design of mixers — Julian came back to the Radiation Lab only late, you know. He wasn't there the whole time at all. And actually when we were worrying about the crystal burnout problem early on, Julian was brought through by Hans Bethe at one stage, and he brought, Hans Bethe brought Julian as a young man — this was in '42 — to worry about the problem we were having about what we called feedthrough for the transmit/receive switch. That was Lou Smullin and I who were doing this. And Julian thought about it and the next morning proposed a way to redesign the resonator for the TR box that might reduce this feedthrough. And we lost many weeks building this thing this way and it turned out it didn't make any difference. It turned out that what he proposed had to be — it weakened the transmission but it also weakened the coupling in such a way that when you adjusted it with the right way to get back where you had to be, it had the same feedthrough.
Pound:So that was the early time, and then he went off to Purdue, where he taught for some time. And then when things got tight he came back to Radiation Lab. And then he — oh, what I was going to say is, I designed a mixer in which I had to have coupling from the — you have to have the local oscillator feeding into the mixer, but not interrupting the flow of the weak signal. And I did, instead of cut and try as we usually did with these things, I tried to use Schwinger's network theory to design this exactly, and it took me days of hand calculations to do, to get the equivalent circuits to all these corners and things that he — and when I got done it really was much easier to have done it just by cut and try.
Rigden:Now at this time you were the section chief for mixers?
Rigden:Did that increase significantly your responsibilities?
Pound:Not really. I had two or three members in my subgroup as it was called, but I shared an office there with the people who were in charge of the crystal development, namely Henry Torrey and Charlie Whitmer, and so we were very close friends and that's how we all of course, Henry and I got together with Purcell on NMR?
Rigden:Yeah. It was a different environment in the sense there was, everything was more, I guess everything was classified, there was security visible. Did that bother people used to freedom in the academic world?
Pound:Well, before I answer that question I might tell you how I made my situation with Zacharias and company, because I was assigned the job of designing or finding out — I'm going to start over again. The lab had decided that they couldn't use bead-supported co-axial lines anymore; they wanted to use stub-supported; stub-supported lines, which means you put a little quarter wave long stub that's short circuited at the end to support the inner conductor, and it doesn't have all this reflection problem of the former plastic beads. But it has to be an effective quarter wave, and at 10 centimeter wavelength, which is what we were using then, there were three sub-bands: 9.1, 10.0 and 10.7 centimeter wavelengths, and I was assigned the job of finding the right length for these stubs for these three different wave bands, and I said, “Hey, there must be a way of combining a couple of things that maybe make it broader band.” So I came up with this idea of broadbanding and combining a half wave transformer — which was known to be frequency-sensitive with a quarter wave stub — and learned from Hansen's notes, Hansen's lectures and so forth, how to use — what do they call them? Smith charts — and solve the problem as to how it worked. And it turned out that that became the way to supplement microwave things. And in fact I can show you that. Let's see. Yeah. And this thing is B there's a patent applied for by the Army Signal Corp.
Rigden:We're looking at a figure dated August 10, 1948, which is “Apparatus for broadband radio transmission, inventor Robert V. Pound,” signed by an attorney.
Pound:Yes. Well, what we had to do was, I had to write a report for the Radiation Lab. And Zacharias, in order to get this report officially approved, and I had to go and see Sam Goudsmit, who was in charge of these things at that time. And this was in the spring of 1942. And Zach took me over to Goudsmit’s office where I was to give Goudsmit a lecture on this device. And I knew the name of Goudsmit at the time, coming from where I did. It was a small scale place, but here was one of the big names that I knew, and so I gave this talk to Goudsmit, and Goudsmit said, “Where did you learn so much?” And so I was rather happy with that.
Rigden:That was nice, yes.
Pound:Because what made my status in the — that was about two weeks after I first came permanently into the microwave business.
Rigden:So that was right at the beginning.
Rigden:Okay. So you established your abilities quickly.
Pound:That's right. With Zacharias at least.
Rigden:All right, back to my question. Did the security issues and the classification and all bother people?
Pound:Well, yeah. Of course it did to the extent that Ajax Allen got shot in the stomach by the security guards.
Rigden:Oh really? I've never heard that.
Pound:No. Well, it was — after one of our Monday night seminars we had regularly, and Allen decided to go back to the lab for something. He was actually in charge of buildings and grounds for the Radiation Lab, and he was challenged at the guard's gate, and he saluted them thinking that they would recognize him and he just drove on, so they shot him. And he had to go to the B to the hospital with surgery for gunshot wounds in the stomach.
Rigden:Was that early in the —?
Pound:No, that was around 1944 or 45. Early we had a simple kind of guarding system with retired Cambridge policemen and such people, but after Pearl Harbor then there was an Army group that came with their riot guns and everything and they stood at all the places. I might say that when I got interviewed for the Society of Fellows, the rather eccentric Englishman, Arthur Darby Nock, who was then acting chairman always used to tell people as to how he went down to the MIT secret laboratory and to see Rabi, who was one of my sponsors at the time, and he said he got — he was so impressed, because he got past the guards there. You know, he got escorted through the guards and so he was quite impressed with that.
Rigden:How much were you aware and others at the Rad Lab in general about what was going on at Los Alamos?
Pound:Rather little in the sense of detail, but rather thoroughly in view of who was involved and that they were into this particular aspect of nuclear physics. Because of course many of our colleagues were recruited away, and people don't generally realize how many of all the important people were at Radiation Lab in the beginning, including E.O. Lawrence and including Backer and we referred to it as Shangri La.
Pound:Bethe, and Ken Bainbridge in particular. He became, you know he was the head of the Trinity Test, and so he, I knew him fairly well from the early times, but it was March 1943 that he was recruited out to Los Alamos. He was the first person actually to have been recruited to Radiation Lab in 1940. Because E. O. Lawrence was a major recruiter for the Radiation Lab, and he came — but that's because he was a friend of Alfred Loomis, who was the member of the — what do you call? — National Defense Research Committee, with Compton Conant Vanevar Bush. And he chaired the microwave subcommittee, and Lawrence knew him very well because with Alfred Loomis' interest in technology he had become the financial source for Lawrence and his cyclotrons. He got his banker friends to help support the cyclotron. So then Lawrence came here to Harvard apparently, as Ken told me, Ken Bainbridge told me, and asked him to come over and walk in the yard where there would be fewer ears close by and talked him into taking leave and coming to MIT which was just founding the Radiation Lab. So he was the very first. He was number one.
Rigden:Well, when the war ended, there was a Time magazine that was scheduled to have the radar story as the cover.
Pound:But it was bypassed by the —
Rigden:It was bumped back to page 82 or something like that, and the bomb took the cover.
Rigden:Did the people at the Radiation Lab feel that they had really been overlooked in terms of the importance of the work that they had done?
Pound:I'm not sure. I think they were also overcome with excitement over what had happened at Los Alamos in fact, but they knew perfectly well that what they — it used to be said I guess you've read in a number of places that they said that the bomb ended the war but the radar won the war.
Rigden:Yes. I think —
Pound:Rabi said that.
Rigden:Well, I think Lee DuBridge said that during the big final talk he gave.
Pound:You mean during the closing —?
Rigden:Yeah, at the closing ceremony.
Pound:Ceremony on VJ Day.
Rigden:I think he said that.
Pound:That's the thing that's in this —
Rigden:Yes, it's in that book.
Pound:Oh, that's that picture by the way, in color.
Rigden:You have said that those years at the Radiation Lab were, quote, “one of the three most exciting and all-consuming of my career.”
Pound:That's probably, that's true.
Rigden:Can you just elaborate on that a bit?
Pound:Well, it was of course the involvement, it was of course the intensity of having to keep going at things and knowing it was going to have some value — plus the fact of being involved with all those, say 50 percent of the distinguished scientists or physicists in the country. And for example it wasn't just physicists either; I spent the evening the other day, well, I spent lunch on Tuesday entirely with Paul Samuelson. You wouldn't expect that he was a member of the Radiation Lab, which he was.
Rigden:He went to Stanford later.
Pound:Paul Samuelson? No.
Rigden:No, no, no. He's the economist.
Pound:He's the economist at MIT. And the reason that he got to Radiation Lab was that he was a junior fellow in the Society of Fellows, and there were two other distinguished junior fellows who played very important roles at Radiation Lab. One was Ivan Getting and the other was Dave Griggs, and they were close, they were contemporary colleagues. And Jim Fisk, Jim Fisk who became president of Bell Labs. They were all junior fellows at that same time that Paul Samuelson was, so they put him into — I can't remember what group he got into. But of course Paul had that particular interest in physics as much. He asks me such things as, “Can you explain entanglement?” to somebody and I said, “Not me, no.”
Rigden:Two more questions on the Radiation Lab. Were you at ease with the whole writing effort at the end when all of you folks were writing these books? By the way, not all were in the writing operation.
Pound:I wouldn't know what you mean by being at ease, because we — I didn't like to spend my time while I was down there sitting at a desk writing, because some of my apparatus was being, had been hijacked into the continuing Research Laboratory of Electronics RLE. And in fact, following a suggestion I had made, Al Hill and Arthur Roberts and somebody else were using it to look for the hyperfine structure in absorption of cesium in the microwave stabilizer. So I would go on kibitz and look at what they were doing whilst I was supposed to be writing the books. And seeing all these people getting on with their lives, and here I was stuck to have to sit down and write this book.
Rigden:Well, my question was — my understanding is that this writing effort was launched by Rabi, who said something to the effect that we didn't write it up all of this knowledge would go to Bell Labs, and he felt that —
Pound:Well, did he put it that way? I see. I hadn't known about the worrying about Bell Labs, but I thought he thought it would be lost, but never mind.
Rigden:And he thought it ought to be available to everyone.
Rigden:And these books became very important after the war.
Pound:They did. Right.
Rigden:So did people see the rationale for that extensive writing effort?
Pound:Oh, I think that they recognized that there are quite a lot of — that the changes and advances in technology of that kind was very, very significant and it shouldn't be lost and we should probably gain the credit for it if that's — I think anybody was taking the credit for it, but I mean you know, people like Brit Chance who had done some great things in precision measurement techniques and so forth, these were things that had to be preserved. And of course my, I have that book I wrote. I don't know if you've ever seen it, but is this the one?
Rigden:I have that book, yes.
Pound:That — this is one of the things that's described in it.
Rigden:And this is the Rad Lab book, volume number 16, Microwave Mixers by Pound.
Pound:And there is the most sophisticated microwave mixer, which has three Magic Ts. That was inspired jointly between me, Bob Dicke and Ed Purcell.
Rigden:Now in something like this, did you present drawings to a machine shop and they made it?
Pound:Well, it's worse than that. This is the rough B this is die casting which we had made by Yale and Town, who were the people who make Yale locks down in Connecticut. But the first model, the test model of this was made by a very distinguished local flute maker.
Pound:William S. Haines, yes. And I went down — we had a man named Jules Simmons who took charge of our getting things made and getting things done, and he took me over to William S. Haines, which used to be over Mass Station in Boston, and I went over there whilst they were machining this thing out of solid brass. And they were doing a beautiful job. And they such — a wonderful thing. And they had just — a man at Case, a University in Cleveland, a mathematician had just died and it was announced in the newspapers that he had a collection of Haines flutes, platinum Haines flutes, and they said they hated platinum because it's awful stuff to work with. But they had one man working on a desk repairing flutes, and everybody else was doing our kind of thing, and so they said would I like to try to play a flute. And I said, “Oh, I couldn't touch it,” and he said, “Do you want to hear the flute?” and I said, “Sure.” So they called a man from the milling machine and he came over and washed his hands and he picked up a flute and he started playing Bach and other things, and he said well, he used to be in the symphony, but he said, “The life of a musician is very tough these days,” so he preferred his life as a machinist. And he was also, they were also making at the time tapered hexagonal — they had metal violin bows they were making, and they were made out of tapered aluminum, hexagonal aluminum, the backing of the bow. And I said how did they make that? Where did they get that from? They said well, they tried all the aluminum makers and nobody would do it so they had to do it themselves.
Rigden:All right. One last question about — When you closed shop at the Radiation Lab, you were certainly aware that a lot of new physical techniques had suddenly become available.
Rigden:As you looked ahead was there a great sense of sort of anticipation as to what would be possible in physics following the war years?
Pound:Well, I think most people thought more in terms of what you could do in the way of accelerators with our microwave technology, and I of course was looking for a way to do something in physics with my limited background. I hated glass blowing among other things, and my mentor Hector for example spent a long time trying to make a vacuum gauge out of a receiving tube, type 59 I think it was, and never succeeded in sticking a pipe onto the side of the vacuum tube glass. And that's because these glasses are not compatible. I mean, you never get glasses with the same expansion coefficient. So that kind of thing put me off a bit on having to get into that kind — And for example my students later have quoted me as saying, “Pound abhors a vacuum,” so [laughter] I was also trying not to have to get into things like molecular beams. But I did think, among other things, that microwave spectroscopy was going to be of an interest. And in fact I had been trying to relearn some physics or learn some physics I had never fully learned, and I got the little book of Herzberg on atomic physics, on atomic spectroscopy, and there was a footnote about the fine structure constant of hydrogen, the wave number of which it said had been measured as .3 per centimeters. And I say, “Hey, that's 3 centimeter wavelength, isn't it?” And I thought that might be something to do, but I never got involved in it as did Lamb. I once mentioned that to Herzberg when I met him in Toronto at one time, and he said, Lamb said that's where he found [out] about it too.
Rigden:Okay, we were just finishing up the comments about the Rad Lab and you were saying?
Pound:Yeah, I was saying something about the ammonia microwave absorption which had been well known from Leeton and Williams from the early thirties, and they had done marvelous things in that they built their own magnetrons to do that with and so forth. And I was quite aware of that, plus the water vapor absorption. But my particular interest at the time was that I foresaw building an atomic clock, because my — one of the things I was most celebrated for at Radiation Lab was developing the technique of frequency stabilization, and all kinds of the early microwave spectroscopists referred to the Pound stabilizer as being what they used to get good signal sources and so forth. And so I, but I had — in fact in my interview with the Society of Fellows proposed using an atomic absorption line like ammonia or whatever to stabilize instead of a cavity which I was using then, because that's not absolute, whereas this other one — And I foresaw using that to measure the difference in different kinds of timescales, and thus I was thinking in terms of — I had been influenced by reading an article about E. A. Milne who had some proposals of kinematic and dynamical timescales by which the difference in the two timescales should change by about one over the age of the universe per year, which meant in those days about a part in 1010 per year if those two timescales really existed, one based on atomic spectra and the other on gravitation or whatever. So that was one of the things that I had the greatest enthusiasm. And then of course what came along was this idea of Purcell's of looking for the absorption of protons.
Rigden:All right, before we get to that, let's go back. You almost provided the perfect springboard. How was it that you got the attention of the Society of Fellows and were asked to become one?
Pound:I was invited.
Rigden:You were doing classified work. How did they know about you? Of course there were these other people there.
Pound:Well, you know the Society of Fellows functions only by nomination by sponsors, and the person that first told me that — My colleagues knew my ridiculous status of never having gone to graduate school, and but it was Al Hill that first mentioned it to me. He said that he had developed the plan of having me, nominating me to the Society of Fellows at Harvard. I didn't know anything about it then, but we had several Radiation Lab people, as I mentioned — Paul Samuelson whom I didn't know then, but the one I knew best was Ivan Getting, and he had been a junior fellow for six years I think, which was illegal. I mean six years was the maximum, but the one that was illegal was Dave Griggs, who had been seven years, because he spent one of those years in the hospital. But he got into Radiation Lab because he flew a plane. Goetting got him to fly his plane as a target plane for testing the early radar, so that's — and then he ended up being part of the Radiation Lab. Of course he got a bad name in the long run for his testimony against Oppenheimer.
Rigden:What was his name again?
Rigden:Griggs. Okay, yeah.
Pound:Dave Griggs. He was a geophysicist while he was a junior fellow. He was using Bridgeman techniques to observe the creep of rocks and he had an experiment set up in the basement here of Jefferson on that subject.
Rigden:You were interviewed by [Alfred North] Whitehead.
Pound:Yes. What they do you see is B and I served on this as a senior fellow about six different years in the postwar era, but they had me come down to Eliott House and they had something like the six Senior Fellows had lunch and then they invited me in to be questioned about what I was interested in and what I was doing, etc. So that group included Whitehead, Arthur Nock, Paul Buck was then provost at the university, and a wonderful man named Fred Hisaw, who was a biologist. We used to call him Mr. Sex or something like that because he was an expert in many respects. He was a Senior Fellow. And I think Henry Shattock, who was one of the old Boston people, once later he told me he was stopped on Beacon Street and asked, “Sir, are you by any chance the late George Apley?” He was a perfect model for such. Anyway —
Rigden:What did Whitehead ask you? Do you remember?
Pound:Well, I think I talked a little bit about the interest in these timescale issues with Whitehead. Because of course Whitehead had his own relativistic theory at one stage. But then they also asked me about what I read, and I told him my wife had put me onto reading Dostoevsky recently and what did I think. Oh, I thought it was wonderful but also very tearing you know. I think it was Crime and Punishment or whatever.
Rigden:So who were some of your contemporaries as a junior fellow?
Pound:Oh boy, that was quite a group, because one of the first ones I met was a man named John Kelleher, who was a Celtic historian and scholar — not a linguist particularly, but he was an Irish American, and I soon discovered, the first day I met him — He ended up being the professor whose professorship was endowed by Henry Shattock. But in any case, he, when he learned I came from Ridgeway he said he knew about the Battle of Ridgeway. And he said — turned out that his ancestors had helped organize the Irish into a raid which became called Penian raids, which was an attempt to take over Canada for the United States — or to drive the representatives of the kingdom out. And this occurred in my home village, and there is now a little museum to it and so forth. In 1866. And these Penians, the leader of this group they called him General but he was Colonel O'Neil in the U.S. Civil War, the Union Armies who had driven back some southern raiders who were raiding all along the Ohio River Valley and so forth, and he was considered an extremely able warrior. And he organized two thousand Irish immigrants who had been in the Civil War as well to cross the river and attack Canada. And it was the Battle of Ridgeway and it lasted only one day, but John and I have had that relationship ever since. I just read his obituary because he died January 1, 2004.
Rigden:Were there any other scientists as junior fellows?
Pound:Not physicists, but there were — Don Griffin was a biologist and very — Oh yeah, and Don Griffin is the man who studied homing of bats — I'm sorry, the homing of pigeons — and he was the man who studied the sonar properties of bats. And he had the help of a retired Harvard physicist called George Washington Pierce, who had studied insects as well and had ultrasonic equipment that he lent to Don Griffin. Don Griffin, he was still with us in a dinner party last week. And then there was a man that helped me, it was a chemist. The chemist junior fellow, Martin Ettlinger, got to use the chemistry professor's laboratories at Radcliffe over in the old Radcliffe Byerly Hall. Ettlinger helped me there was — he helped me make solutions of gallium chloride — that I could look for the NMR. I measured a lot of nuclear magnetic moments using NMR. Another distinguished biologist was Carroll Williams who went on to discover a growth hormone by his studies of insect physiology.
Rigden:When did you start your tenure as a junior fellow?
Pound:Technically July '46, but I actually was involved from July '45.
Rigden:So when you did the NMR work you were a junior fellow?
Pound:Yes. And lot of people suspected I think that I got appointed because I had done the NMR work, but I was not; I was already appointed before that came up.
Rigden:All right. Well let's now look at the postwar world. Just a general question. When the war started physics was really interrupted.
Rigden:And there was building intensity in physics in this country in the late thirties. And then everything stopped, and now suddenly the war is over. Was there a sense amongst you and your other friends that you were going to pick up where you left off, or how did you sort of think you were going to get started again?
Pound:Well, I think, well as I say, in the dismantling of the Radiation Lab I saw all those people going back to where they'd come from mostly, and the dominant thing of physics in those days was of course nuclear physics and cyclotrons and all that. And Harvard was rather limited in that respect because it had lost its cyclotron to Los Alamos. And Ken Bainbridge, who had built the cyclotron before the war, and it was quite successfully operational before the war, whereas MIT had attempted to build one that didn't work very well, so they used the Harvard cyclotron quite a bit. And I profited from that a little bit in the postwar era because they were generous to us to use the postwar MIT cyclotron for radiations occasionally. And so, because they felt an obligation from our willingness. But anyway, no, I think people were certainly looking for using the new technologies, and of course people like — one of the most distinguished people at Radiation Lab was Jim Lawson for example, and he went off to General Electric in the new Knowles Lab I guess it was. But he in particular oversaw the building of a betatron there. Now was it a betatron or a synchrotron? I think it was — I know that he sent some information at one time about the volume of stuff that the pumps had succeeded in pulling out of there. It was tons. It was amazing. But anyway. So if you've read Alvarez's book, people like Alvarez and Bill Hansen, they all tried to make accelerators and apply that aspect of the technology.
Rigden:So that was the big initiative after the war.
Rigden:All right, talk about your lunchtime, going to lunch with Purcell and Torrey.
Pound:Yes. Well, I had been in the habit going out —
Rigden:This was summer of '45? No, later.
Pound:Yes. It was after VJ Day in the fall of '45.
Rigden:In the fall of '45. Okay. Go ahead.
Pound:But I, with a man that went to Yale after the war, Bob Beringer, used to go to that lunch there for quite a long time quite often. I would go over and Bob Beringer worked in the same room with Bob Dicke, and sometimes we'd get Bob Dicke to go up there to this Hennesey’s Bakery and Deli for lunch. For 40 cents you'd get this marvelous lunch. They made their own bread, they made their own Boston cream pie, and all these things. It was a bakery and it was a delicatessen.
Rigden:What was the name of it again?
Rigden:Hennesey. Okay. Go ahead.
Pound:And so then as things started disintegrating B I don't know whether Beringer was still around, but he ended up at Yale building accelerators at Yale. But Henry Torrey and I occupied this, Henry Torrey and I had the same office suite, and so we went off to lunch that day and said, “Let’s see if we can get Ed to go along.” Ed [Purcell] choose a different group. We weren’t in his group. He was down the hall and across and I used to spend a lot of time over in his office because in what I was doing in this thing, the Magic T and all, was very close, that was their concern. And so, and another person in his group that I spent a lot of time with was Carol Montgomery who was the co-author with them on that book. He died soon after the war but — And he had been Bob Beringer's thesis advisor before the war. They did the first directional correlations, they did the directional correlations of annihilation radiation, positrons. Anyway, so we picked up Ed, and he said, “Sure, okay,” and he went along. Of course we walked from 77 Mass Ave. up Massachusetts Avenue to Central Square. And it was in that walk that Ed, knowing that Henry had been a member of Rabi’s group, asked him this question about whether you think that you could detect the absorption of a two-level system of protons in a magnetic field as an absorption. And he thought, they used to talk about that at Columbia. And of course that was the after effect of [C.E.] Gorter.
Pound:And but Henry couldn't remember quite why they didn't think it would work. So he went home that evening as I've said I guess, that he went home that evening and as was his wont — he always loved to calculate things, and so he did some calculations and he got quite excited because he decided, “Hey, it should be possible,” and he went the next morning to see Ed and told him, and Ed said, “So let's do it.” So that's the way it got started.
Rigden:Well, do you remember there were calculations by Teller and there was one —
Pound:Heitler and Teller.
Rigden:B that said that the relaxation time was eons. You know, I mean it was —
Pound:No, they didn't say that. They said, well, Teller — the Heitler and Teller calculation, which Henry found in his search — You see, what happened was we decided to get started on that, and then Henry started thinking, you know, “I assumed thermal equilibrium when I did this calculation. I wonder how that comes about?” And we went over and talked to Ed and together. Henry said he would do a literature search and try to find what happened, what would be the case. And he came up with this paper of I. Waller.
Rigden:I. Waller. That's what I was trying to think of, yes.
Pound:And I. Waller had calculated for electrons, not nuclei, and Henry sat down and converted it to apply for protons as compared with electrons in solid and he came out with a view that it might be an hour or so. But he made some — And this was that he realized it was not the first order effect but the second order effect that dominated because that allowed you to integrate over the whole spectrum of phonons and that at room temperatures and well above the lattice temperature you could have that help, and so he gave out with the view that it might be some hours. But it turned out that he used incompatible numbers in the long run. If he had done it right he would have been more discouraged in the hours because our system was designed to work even though it would be hours. Because once the relaxation had happened our big cavity and the rf level we would use with it would be so low that it wouldn't disturb the equilibrium significantly in less than several hours. And that was one of the reasons we used this big cavity instead of a coil. But the other reason was that we were so immersed in microwave technology and so forth that we never thought of not, of just using coils and capacitors.
Rigden:Let me ask a little tricky question I think. You and Torrey and Ed Purcell, when you were walking to lunch you were all young and you were all early in your career. What established Purcell as the head of that experiment?
Pound:Well, he had made the suggestion. He raised the question of could you do it, and as you say, it was the fact that in his book writing he had been writing down the history of the discovery of the absorption due to water vapor, and he came to the realization that there were just two particular levels whose energy difference was just equal to that frequency. And although there was a system of hundreds of levels, and if anybody looked at it carefully enough they might have discovered that particular pair, but [David M.] Dennison I think it was at Michigan had published from infrared spectroscopy a description of all those energy levels of the water molecule. So and of course there you didn't have a population problem. Well, it's the same differential population for those levels because of their energy difference, but it's populated at the atmospheric temperatures through a very large number of those levels. So he said, “But you can get a two-level system in absorption by making the frequency match the energy of the energy gap,” and so that was the question that started the whole thing, and that's nominally what made him leader. Although in a sense I think that all three of us were pretty important to it.
Rigden:Ed told me that when you were doing that experiment that you, Bob Pound, knew more about — and I think he said signal-to-noise — than anyone in the country.
Pound:Well, I think that's an exaggeration, because there were some people at Bell Labs, and there was a man who ended up for a while at British Columbia and then at Michigan, Michigan State, who wrote books on these subjects. But there was a man named Rice. I gave a course here when I was a junior fellow on limits of sensitivity and detection and so forth which actually was under, oh, engineering science and applied physics department, a predecessor of applied science to the division, and that was in '47. Was it spring '48? Maybe. But I learned an awful lot of that, and the real details of what I could talk about from my having the manuscript of Lawson and Uhlenbeck, which was one of the Radiation Lab's books, and that was really the best work of that kind that existed then.
Rigden:Do you see your role in the Purcell experiment sort of analogous to Hansen's role in the Block experiment?
Pound:Not that much, because I think that Hansen's role was greater than most people realize, in that he was the man that really understood how to make the thing work, the circuitry and everything. And I have seen his notebooks from May of 1945, which was well before we even thought about it, in which he was designing a balanced amplifier for this thing. Then he had a question under this that said something about how the nuclei would react to this or that. I don't remember exactly what the question was, but at the bottom he said, “Ah, but leave it to Felix.”
Rigden:But you essentially designed the apparatus, did you not?
Pound:Pretty much, yeah, I guess so. Well, Ed and I participated in designing that cavity, and I had my technician build it. I had a very good private kind of — Charlie Rowe, who had been my sort of electronics and machinist private guy in my little subgroup there all through the last couple of years, and he hadn't anything much to do and was waiting for an opportunity for his new job after the war, so I put the drawings we had made and asked him to build it, which he did. And he was very good. And actually my college mentor, Grant Hector, hired him after the war to National Union Radio Company which he had taken on as the head of something or other. Because you see he had spent the war years after I left, then he left and joined Merle Tuve in the proximity fuse development. So he became very involved in making these little hearing aid, well, these little vacuum tubes for proximity fuses.
Rigden:Let me say — I should have probably made it clearer. When we just talked a little bit about the walk from MIT to Central Square, this was the discussion that launched the discovery of NMR in bulk matter.
Rigden:Which of course has had enormous significance in the following years. And so Bob Pound was a part of that along with Ed Purcell and Henry Torrey. Why don't you just tell us about the experiment?
Pound:Oh, well, as I say, the experiment was based on using a balanced bridge. In one arm the cavity that contained the absorbing sample, which was paraffin wax. We had about 2 pounds of paraffin wax in this cavity, and that's some stuff that Purcell had bought at the little local grocery store on the way over that evening. And we melted that and poured it into the cavity. And on Thursday, the 13th of December, we spent the evening trying — We had everything set up. I brought everything up from MIT. The only thing is Harvard — it's always called a Harvard experiment, but the paper is published under the byline of Radiation Lab MIT. And, you know, that's right. All of three of us were full-time employees, and we were doing this clandestinely. And I once said that in the presence of Al Hill and he said, “I knew what you were doing!” So anyway, the 13th of — we met in the evening of that Thursday, and I have told various people about this fact that I had that afternoon read that article in The New Yorker in the “The Talk of the Town” which is describing the discovery of nuclear fission, and that J. R. Dunning of Columbia had been hearing that talk from Bohr which was given at — it was at the New York Physical Society Meeting I think.
Rigden:I think so.
Pound:And he heard that talk by Bohr, and he decided he wanted to see for himself, so after the talk he went back to the lab at Columbia, set something up and saw these big flashes of tracks on his — I don't know what kind of detector he was using, but they were big things that indicated he was seeing this big energy from the fission. And so then The New Yorker said he closed it down and thoughtfully went leaning into heavy weather. It was pouring rain or something like that, and walking, contemplating about the new world that was opening up this way. So when we had that Thursday night there was a snowstorm here. And this was almost the first time I'd been here. No, we had come over in preparation for that experiment. We had to measure the field of the magnet and we got — Ed had the machine shop here make new pole pieces to try to get a uniform field and used Rose shims on those pole pieces which turned out to be overdone. And but we brought down from the attic, from not the attic, the fourth floor electricity lab, a wall galvanometer called a ballistic galvanometer in order to measure the field with the flip coil technique. Of course nowadays the student would say, “Why didn't you use NMR?” But anyway, so we used this flip coil and calibrated the field. And I don't know if I ever showed you that. Did I ever show you that —?
Rigden:Let's just pause a minute. I'm going to switch the tape. Okay. We were talking about calibrating the magnetic field on the night of Thursday, December 13th.
Pound:No, that calibration was done sometime before that, I mean a couple of visits before.
Pound:And we had the thing, the magnet, calibrated and the pole piece, that was after Ed had had the pole pieces modified by the machine shop here. And the other item that Harvard's contribution was the general radio signal generator. It was applied as a 30 MHZ source. Other than that and the magnet the rest of it all was stolen from MIT. I use the term stolen as a euphemism I suppose, but one of the things that came from MIT was also, it came out of my crystal test set thing, was this Hallicrafter high-frequency radio receiver. That performed the main amplification and detection whereas it was preceded by an MIT Radiation Lab preamplifier that was used from radar, because, see, 30 MHZ was the frequency of the intermediate frequency radar, and so we had the very lowest noise amplifiers available in those days. Henry Wallman designed that fancy circuit which got the noise figure down to 1 or 2 db, and that was at the front end. So, and then it fed the Hallicrafters, which came from my apparatus in my lab at MIT and it had a meter at the output which was the only way of seeing the signal. You watched this meter and you would balance this bridge by adjusting the amplitude on one arm compared with the other, adjusting the frequency into the peak of the transmission through the cavity, and then balancing it down by adjusting the intensity and the phase. And the phase was adjusted by using little line stretchers that were intended for 10-centimeter wavelength and here we were working 10-meter wavelength, so we had a line of these things so that you could get enough adjustability.
Rigden:But Bob, go back to Thursday evening. You were talking about Thursday.
Pound:And then by Thursday everything was together, and then we started trying to see if it would work.
Rigden:So you actually started the experiment on Thursday evening?
Yes, we started the experiment on Thursday evening, which meant turning on the magnet and getting the water flowing through, the water cooling on the big magnet. And the control of the magnet was a rheostat on a panel on the wall, which was many feet away from where the experiment was, and the meter sat on that table, and everything in this balanced bridge was terribly microphonic so you didn't want to touch the table or anything when it was balanced down. Because you could only balance it down so far, because the frequency sensitivity of the two arms of that dumb bridge were different, because one had the cavity and the other just had an untuned attenuated path. So you could only balance it down to about, by 60 db or so, because the noise sidebands weren't balanced in the same way on both sides. So that would determine how much rf level we could use. And then we adjusted it down until we could no longer balance more and the meter was standing at, reading noise, so then we started adjusting that rheostat around the field which this calibration said would be the right value, because we knew the g value from Rabi. And we worked from mid-evening until three or four in the morning trying, rebalancing and adjusting and so forth. No result whatsoever. So finally I had to go off in that snowstorm without the contemplation that I could think about what was happening in the future. I was the only one that had driven, and I drove Ed back to his house and Henry back to where the Torreys were renting and living down near Mt. Auburn Street, and my wife Betty had been with Henry Torrey's wife, Helen.
They spent the evening together wondering what we were finding, and I had to say we hadn't found anything. But we made a compact about coming in on Saturday, thinking maybe it was the relaxation time, it was too long. Although having spent all that time, it was relaxing all that time, when you think about it. Because the field was on also at the time. So anyway, Ed agreed to come in around seven in the morning on Saturday and turn the magnet on and let it cook until we would come in. Because in those days we still were expected to work on Saturdays in principle, although I don't think anybody would fine us if we hadn't. But we came in about two in that afternoon and then we started all over again. And the same effect. Everything happened. Nothing happened. The meter never made the bumps. So, about late afternoon, 5 o'clock or so, we decided, “Well, let's shut it down and try to think of what we might do to improve things.” And I said, “Why don't we just turn the magnet all the way up?” That magnet, that generator which was in Cruft, remote from there and it was the field control we had there — it was very coarse — we turned it up. It was 100 amperes at 500 volts, so that was a lot of power. We turned it all the way up to the top and then came down slowly. And as we came down through 80 amperes it went bump. There it was. And that's because in this calibration we were seeking it at something like 73 amperes.
Rigden:Seventy-three amperes I've recorded.
Pound:Yeah. And it turned out it happened at 82 amperes.
Rigden:But why, given the uncertainties, did you stick with the 73 for so long?
Rigden:Why didn't you just explore?
Pound:Well, we did. We went plus and minus 10 percent relative to that thinking we couldn't be wrong by more than that.
Pound:And the fact was we were wrong by more than that — not because our calibration was wrong, it was fine, but it was what we had forgotten and didn't look at it properly was that the magnet was saturated. So it took all that more amperes to get 2 more percent field. We were only off 2 percent in the calibration, which is pretty good for that kind of system, but it took 15 percent more current in order to get that 2 percent more field.
Rigden:So it was on Saturday 15th —
Rigden:— that you discovered the first absorption of hydrogens in paraffin.
Pound:That's right, that's right. And one of these pieces of paper has Henry's signature on it — not Henry's signa — Oh, there is a copy of the circuitry, but — Yeah, well —
Rigden:What was the reaction of you and Ed and Henry when that happened? Were you elated that you —?
Pound:Oh, yeah, we were very — we first saw that we had now something to go with to what we could see what we were going to be doing for a while. And I would give up my ideas of building another atomic clock for a while — although I was supposed to be. At Harvard there was a — you know E. L. Chaffe was. He was the main electronics specialist at Harvard who built big vacuum tubes and things. But he ran the electronic research lab, and he had some graduate students. One was going to make an ammonia-based atomic clock following my suggestions. That guy got — he went down the wrong route because he instead got enthused not about how the stabilizing system how well it worked, but rather to see what you could do without stabilizing it by stabilizing all the power supplies and protecting the temperature and everything. So that didn't get us anywhere.
Rigden:Well you've already suggested it. I'm going to ask the question. When you found that you —
Pound:That's the one that's Henry's writing.
Rigden:Okay. All right. When you found that you had succeeded on this NMR experiment, that put your thoughts of atomic clocks on the side burner or back burners, and did you sort of quickly decide that you were going to pursue this for a while? And in fact it had a major influence on your career.
Pound:Yes, except that it was always in the back of my mind that I might discover a reference system for the concept of the atomic clock that would be better than the ammonia one. And in February of '47 Rabi came and gave a colloquium talk. And in that talk he talked about the work of [Willis] Lamb and [Bernard] Feld, which was discovering quadrupole splitting in molecular spectroscopy in molecular beams. And I went away from that saying, “My God. Surely we will have something like that in perfect crystalline solids” and so forth. So I immediately began pursuing the idea of quadrupole resonance as distinct from nuclear magnetic resonance. And it's for that reason that I built the frequency-scanning marginal oscillators because with quadrupole resonance you have no control over the frequency. It's whatever the solid gives you. So you have to have something you can scan in frequency. And at that time it was almost impossible to make a system sensitive enough it could be flexibly scanned in frequency. So everybody did their NMR by scanning the field, and that brought it through a fixed frequency. There was no problem.
Rigden:Yeah. Well, we'll come to quadrupole in a bit. Let's go on to your paper in '48. One of the most cited papers I think in physics is the BPP paper — [Nicolaas] Bloembergen and Purcell and Pound. How did you get involved in that collaboration?
Well, I was part of the advisory system when Bloembergen came, and since Bloembergen arrived in the beginning of '46, and Ed got him, appointed him as a research assistant. And I oversaw most of the — I educated him in the electronics aspect of doing this, and we decided to go for full modulated lock-in amplifier detection system and so forth. So I was part of that whole project from the beginning, including making the apparatus, and then I participated — we spent a lot of time looking to try to find other nuclei, but that magnet which ended up being powered by a bunch of big storage batteries, the current was controlled by a sliding — what do you call it? It was a battery clip sliding along a invar strip or — what is it? — to vary the current. And you looked at this output meter, the lock-in amplifier that was always joggling away when it was up to the sensitivity of the noise and you tried to find the magnetic resonance of say bromine or something else.
We had seen fluorine of course in the original cavity and the first thing we put Bloembergen onto was to look for the fluerine 19 resonance and with the old cavity, which ended up destroying the old cavity in a sense because that stuff we put in it corroded the hell out of the brass. But anyway, we never found any other magnetic resonances with that system because you had to watch and slide this clip along the maganin strip. But we also did most of the thing as Bloembergen had pointed out that I was the one that showed that you could move this sample around to find the most homogeneous place in the field and get the narrowest line we'd ever seen out of the protons and started to realize about fluctuation narrowing. And I came — my own idea, you know, I think I really brought up that issue because after we'd found that I went home and that evening I was — I used to think in my Radiation Lab days largely in terms of Fourier transforms and so forth and was thinking about frequency modulation and what happens to the sidebands in frequency modulation, and it depends on rates as compared with distance in spectral fluctuations, and I realized things average out. You get this narrow thing. And I came in in the morning and said to Ed and Nico that I felt that I knew that it was the fluctuations, and that's how we got started in the whole fluctuation narrowing business. At least we would have started anyway, and then we went and did it much more formally, and which Ed dug up — what is it? — theory on correlation functions and so forth. I always remember that [J.H.] Van Fleck was our mentor in a way, because Ed always told Van what was going on. And when Van read about this and saw our paper coming out, and he was thinking about Weiner, and he said, “I think you ought to refer to the sausage.”
Rigden:Refer to what?
Rigden:Well, that was a very, very important paper.
Pound:That's right. I think that the people in the magnetic resonance in medicine are pretty aware of that too.
Rigden:When did the Pound Box come in?
Pound:Well that's, you see I started that in order to look for the frequency scanning technique, looking for quadrupole things. So I started that in February of '47.
Rigden:Explain what the Pound Box is.
Well, it's really an oscillator held at a level close to threshold so that if it experiences some variance in the rf energy storage situation in its coil it will show up as a change in level. And if you use lock-in amplifier technique and all that, you can do it all through that game and do the same sort of thing that you do in conventional fixed frequency stuff. But the big trouble is that it supplies the rf essentially to drive the NMR and also does the detection, so it works almost like what I was used to in ham radio from listening to a c.w. signal, because there you let it oscillate and you hear the heterodyne between its own self and the incoming signal. And so I went forth, I used this before I was able to find any quadrupole effects to look at a lot of NMR magnetic moments, including phosphorous 31 and quite a list of them. I think I had about ten different nuclei that I studied that way. But then — and I had, and you asked me about other scientists in the Society of Fellows. One of them was George Kennedy, George C. Kennedy who ended up, he was really a follower of Griggs in a way, because he was a high-pressure geophysicist and he ended up on the faculty here for a while but he ended up at that UCLA institution run by Louis Slichter I think it was. But and he was a junior fellow. He had made his reputation at the Bell Labs developing crystal-growing techniques.
So I got his help to learn how to, a technique to grow a certain single crystal. And the crystal we grew initially was lithium sulfate monohydrate. And I looked at the lithium-7 magnetic resonance in that and found the structure due to its interaction with the quadrupole. I decided to do that. Originally I hadn't been interested in — you could predict where there would be some quadrupole resonances from the knowledge that came as an interaction in molecules in microwave spectroscopy which was going on broadly, but I wasn't interested in these molecular things because I had this naive idea that I could solve Rabi's problem of getting a quadrupole field gradient by having a perfect ionic crystal and calculating the field gradient from the charges looked at as point charges on the lattice. That turned out to be hogwash, because there's the [R.M.] Sternheimer effect which turns out to mean that the atom gets heavily polarized and contributes much more than — we have to know all kinds of atomic structure interaction problems in order to evaluate that. So it never really was successful in that respect, but I ignored going to look for things that would have been simple to find, and that's why I got scooped in the pure quadrupole business by [Hans] Dehmelt and [H.] Kruger in Germany who looked at chlorine in — what is it? It's in a chlorine ethane, dichloroethylene or something like that and —
Rigden:You were right almost there, weren't you?
Pound:Oh yeah. I had already done — I had decided — it was a needle in a haystack. Actually I have a notebook full of calculations of the field gradient by assuming this thing from mercuric sulfide, HgS and I was going to look for that because it's a nice hexagonal single crystal and I was trying to grow a single crystal. You didn't have to have a single crystal in fact, because if you didn't have a magnetic field there was no directional sense and therefore you could deal with the powdered version and you get a single frequency even so. So I started looking for that, but then I decided this is really a needle in the haystack if you don't really know the field gradient and you don't know the quadrupole moment. So I decided it would be easier to look at light elements where the quadrupole interaction would be small and look for structure. So that's what I did, and then I used corundum the most significant one was the aluminum-27 which I did a lot of study on, which demonstrated it through the second order interactions and so forth.
Rigden:This was in the fifties?
Pound:No, this was in '47.
Rigden:'47. Oh, all right.
Pound:Or '48B it was only published fully in 1950 but in abstracts in 1948.
Rigden:Well just let me wrap up one thing. The Pound Box, that got picked up and that was in labs all over the place.
Pound:Well, the first publication —
Rigden:Did you patent that?
Rigden:Did you patent that?
Pound:No. The patent situation for NMR was impossible because [Felix] Block and Hansen had made such a broad patent and succeeded that you couldn't do anything against it. I spent a lot of time consulting with a company called — well, Perkin-Elmer in particular, who wanted to get into NMR, because they were being pushed out of IR. They were the big name in infrared spectra, but they thought they should get into NMR, and this was around 1950 when Rex Richards, who was from Oxford, came over. He was well-versed in the infrared spectroscopy game but he picked up at Oxford as a chemist NMR in his own right and he became a consultant to Perkin-Elmer when he came over here too. But anyway, in the end they had — I saw a lawyer concerned with what that patent that Bloch and Hansen, how strong was it, and they concluded it could be broken because it was overplayed but that it would cost a lot of money, and Perkin-Elmer elected not to go with it, so they never did. Because it would run out eventually.
Rigden:And was the patent the basis of Varian's getting into —?
Pound:Yes. In fact, in the fall of '47 — was it the fall of '47? No, it was the fall of '46. Yes, it was the fall of '46 I was at a party at J.B.H. Kuper’s. The man that was the editor of RSI for many years, head of the components group or electronics group at Brookhaven but was a friend at Radiation Lab. He is in that picture with me and Henry in the Nice Years book. Anyway, he had a cocktail party at the time of a meeting of the Physical Society in New York in the fall of '46, and Bloch came and told me that they were proposing to patent nuclear induction and would we want to join them. And I said I didn't think so. Actually, as I thought about it later I figured you couldn't do that because you can't join two independent groups in a single patent like that. That would violate the rules. And I came back and asked Ed about it and he had no interest in it. And so, but Bloch had told me that he and Hansen were patenting it and were going to license it to the Varians because he felt that they had been shortchanged. They felt they had been shortchanged on the Klystron because of the war. You know, that was sort of taken away from them as a going thing. So he did that. But now they wrote this patent and they had this man named Hunter who did their patent write-up and they wrote the description of it as if it were a textbook in nuclear physics, and I think that so dominated the whole picture that it looked as if they had invented nuclear magnetism and everything in that patent. Their patent was filed December 23, 1946, one day before a year had passed after our paper was received at the Phys. Rev.
Pound:And then a little later, two years later, they had it reissued in which they changed all — they had all the same claims but they were written in italics in their final patent, in which they changed from nuclei to parts of atoms. And that was so it would extend to electron resonance.
Pound:EPR. And there I think was the built-in vulnerability, because after all EPR had been invented before in Russia by Zavoyski. And so that could have been cited as a prior art for them. So they wrote it in such a way that there was no distinction in the technique. I claimed that their patent would have been excellently justifiable if they made it specifically to the crossed coil concept and picking up of procession. But quadrupole resonance doesn't show that for example, so my technology for looking for quadrupole resonance with marginal oscillators and so forth wouldn't have worked with crossed coils.
Rigden:Is there anything else that you think I should ask you about the whole NMR period of your life?
Pound:Well, a lot of question often arises as to whether we had any anticipation of its getting applied to medicine and such things at that stage, and my answer to that would be somewhat like Ed's. We wouldn't be at all surprised about being able to observe NMR in human or other living matter, but that we had no knowledge or expectation of the power of computing that was going to come up, and that's what really made the big difference.
Rigden:How long after was it that you saw NMR being applied by chemists?
Pound:That took a little while too. In fact we used to tell chemists that, you know, you have to have sizeable amounts. It's not an analytical sensitive thing for chemists. They are not going to be interested in it. But it was only after the realization of the high resolution aspect and the fluctuation narrowing and so forth that one realized that you could see very small amounts, because the signal-to-noise ratio became so much better because of the narrowness.
Rigden:And chemical shifts came in.
Pound:And chemical shifts came in — well, both chemical shifts and — what do you call it? — spinning direction things and so forth, yeah, with all that structural stuff. It's amazing. You get the spectra with forty-seven different lines, all attributed to different structures in molecular things. So it soon became true that no working chemist could be without an NMR spectrometer.
Rigden:That's right. And that was true certainly by the fifties.
Pound:Yes, middle fifties I'd say.
Well listen, it's almost noon. We're through —
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