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Interview of Merle Tuve by Charles Weiner on 1967 March 30, Niels Bohr Library & Archives, American Institute of Physics, College Park, MD USA, www.aip.org/history-programs/niels-bohr-library/oral-histories/4920
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Early interest in physics in South Dakota: early training as a physicist, Univ. of Minnesota in early 1920’s: acceleration of positive ions and electrons; teaching at Princeton, 1923: doctoral work at Johns Hopkins, 1924-26; pulse radio and ionosphere experiments, 1925; work on high voltages with Tesla ciols for proton acceleration, Dept. of Terrestrial Magnetism, 1926-31; obtaining funds for research, effect of Depression: building Van de Graff machine, 1932: connections between theorists and experimentalists in Washington-Baltimore region 1925-1930s; disintegration of light elements, 1932: reaction to discovery of neutron, 1932: experimental work on proton-proton and proton-neutron forces, 1934-36; organization of Washington conferences on theoretical physics, collaboration between Carnegie Institution and George Washington University, 1930s; early fission experiments, 1939.
I‘d like to start pretty early in your career and ask you how you got interested in physics…
Let me preface my remarks by saying I’ve made no preparation for this discussion this afternoon, although I had word here two days ago that you were going to talk about the early days of nuclear physics in the U.S.A. I have not tried to refresh my memory at all in reference to any reports or anything. How did I get interested in physics? Well, it’s a long story. It goes back to the fact that my dad was one of the early Scout masters in the United States, in Canton, South Dakota, in 1911. This must have been only a year or two after Thomas Seton started the scouting movement in the U. S. I was too young to be a member of the Scouts, but they allowed me to trail along on some of the hikes; so I got to know the friends of my older brother, five years older—Lew, we call him. What happened was that some of the boys got interested in wireless telegraphy. I think they had been reading the early publications by Hugo Gernsbach, which I did, too. Electrical Experimenter was a slightly later thing. One of the earlier magazines was Modern Electrics, remember reading that back in 1912 and 1913.
Did you subscribe to that?
No, you could buy it at Sherman and Roche, the corner drugstore downtown in Canton; and I remember haunting their magazine files to pick up some of these. You know, along with Popular Mechanics, there were these electrical things. To help them along, the Scouts gave a minstrel show. I don’t remember anything about the minstrel show except a couple of the boys blacked their faces. They were end men or something. They gave the show in order to buy money for wireless equipment from the Electric Importing Company in New York. Well, it took nearly two years for that stuff to arrive. It took a long time. By that time the older boys had lost interest, so Ernie Lawrence and I inherited this equipment in my dad’s basement. This was spark equipment—a spark coil with a tuning condenser and coil and a receiving tuner, an electrolytic detector, some Brandese headphones, antenna insulators for wire and so on. Ernie and I had been friends with the telephone repairmen anyway. As they did electrical repairs, we got their cast-off batteries, to make bells and motors run and so on. We inherited this wireless equipment, after some persuasion of my dad, and were allowed to set it up. That must have been some time in 1913 or early 1914. By 1915 and ‘16, we had of course gotten along quite a bit further ourselves. I believe it was the summer of 1915 that Ernest and I helped build the golf course greens in Canton in order to earn money to buy the first vacuum tubes. We had seen, on a trip to Sioux City, one of the early deForest Audion tubes used as a detector. There was a fellow whose name was White, the son of a doctor down there, who had radio equipment when we went down to a YMCA meeting.
Were these demonstrated?
We visited his home one night. This was really thrilling, especially when you could hear the spark transmitters of amateurs up in Minnesota and further off in Iowa, using this glowing Audion tube, We determined to get money to buy tubes, Ernest bought a “pliotron,” it was called—a tubular thing. I bought a deForest type T—this meant tubular—Audion. We couldn’t buy the round bulbs. They were reserved for the Navy and shipboard equipment, very expensive. So the blisters on the golf course greens earned our first good detectors. By 1916 we were both listening—I had built some long-wave coils—to long-wave CW radio. Ernest had long, very tall vertical loading coils. I had bought from Clapp-Eastham Company—these are famous old names—a set of their long-wave tuning coils, and we used to listen there in South Dakota to San Francisco, Arlington, and Tuckerton (New Jersey). I took down each night the 15-minute news reports from NAA Arlington. And also, of course, I was very much interested in setting my watch accurately. I had a pretty good watch and each day took time signals. By 1917 we were listening to OUI and POZ. These were Hanover and Nauen in Germany, and of course Tuckerton, New Jersey, was the long-wave commercial set on this side of the Atlantic. During these years we were in high school. Actually, I went only one year to high school with Ernest, and then I went on to a Lutheran Academy which my father had been head of there in Canton, called Augustana. Let’s see, I only went three years to secondary school, and then I found I had credits enough to graduate, and so I did. In my third year I took high school physics under a Professor M. N. B. Minne, and he opened the door to the luxury of really understanding a lot of things. Newton’s laws just fascinated me, I’d heard about them. But that these things could be so simple and straightforward was extremely interesting to me.
Was this a semester or a year course?
It was a year course and not too difficult, but we had some laboratory work and so on. My father died that summer, in July of 1918, and I had finished then in June. He was one of the first victims of the Spanish flu in 1918, although they didn’t recognize it. They didn’t know really till September and October what the epidemic was. I had also gotten interested in chemistry. I actually took a college course in chemistry. It was given at the Academy. They also had two years of college at this Academy. When I went to the University of Minnesota, where my brother had been a student after the war, I started in chemistry. But really found it was too much memory work as far as I could tell, and switched over to electrical engineering. But in electrical engineering I persuaded them to let me take as much physics as possible.
What career goal did you have in mind?
Well, I never knew that I could stay in college more than one more quarter at any one time. My father was dead; we didn’t have any money. My mother just moved the family up there. My brother was a sophomore, I think, in college at the time my father died, and I had just finished prep school. My sister was four years younger. She was somewhere in the grades, and I had a kid brother—Dr. Richard Tuve here in town at the Naval Research Lab—who was I guess six or seven when my father died. So we didn’t know just how to do it, and each quarter I tried to take the courses that would really open the most doors for me. It was a very stimulating way to study because you never knew whether you could keep on. I was lucky. They taught physics for engineers there at Minnesota over in the physics department. The three men—Erikson, Zeleny, and Miller— separately handled the different parts. It was interesting enough that I asked permission to take theoretical physics, which was a first year graduate course, at the beginning of my junior year under John T. Tate. Of course, this sealed it. By the time I’d been six weeks in that course, I really thought this was just superb. You know, I was just trying to furnish my mind. I wasn’t expecting to make any career of anything. I still don’t know why they’ve given me a Carnegie salary all these years. The fact is that I was just interested to know about these things as much as I could, and whatever I did—selling groceries or anything else—that would have a knowledge of physics and mathematics that could think about. It didn’t occur to me till later that you could make a business of your avocation. My first year of college I started in April, because my father had died the previous July. So it was interrupted, but I went to a couple of summer terms, and finished college with my old classmates in 1922.
Was Ernest Lawrence also at Minnesota?
Ernest finished in 1922 at the University of South Dakota. He had gone to St. Olaf in 1918 and then to the University of South Dakota where he studied physics with Professor Akeley. This was the brother of Carl Akeley, the explorer. He was professor of physics down there at Vermillion, South Dakota. At Minnesota in advanced courses and for graduate work we had Swann and Tate, especially. There was a long record in the Department there of forward looking in physics. Arthur Compton had been there for a year previously. Quite a few people had been through the mill at Minnesota and gone on to other places. I had persuaded Ernest to accept a teaching fellowship, and he came up there. He worked with Swann, and I worked with Tate, setting up vacuum pumps and ionization detectors. I stayed there and took my master’s degree. Actually my master’s thesis was on ionization of mercury vapor by positive ions, under Jack Tate. Tate’s method of teaching was rather different from Swann’s. Ernest managed to get all kinds of help out of Swann. Swann had his apparatus parts made in the shop, and Swann’s technician nursed the work along and so on. Tate just inquired what I was interested in and said, “Well, all right. You’ll have to get a pump and a suitable detector,” but he left me entirely alone. After a while I felt pretty ineffective. I said I wanted to do something in ionization of positive ions, but as the year drew on I wasn’t getting anywhere. I went to him and said, “Listen, I’m not going to be able to get a degree out of this. I’m supposed to go to Princeton next year.” I had applied and received an appointment as instructor under Karl Compton at Princeton, said, “I want to finish my master’s here.” He said, “It’s up to you.” I said, “What the hell—you aren’t helping me a darned bit. How can I make a thesis out of this? I just don’t get any ionization.” He said, “Well, that’s up to you. If you don’t get ionization, what does that mean? What about it?” He didn’t help me, and I went home the most discouraged guy in the world until I realized the next day: “Well, he was trying to tell me in his own way, without robbing me of finding it, that to find there was practically no ionization was probably as important as if found out there was ionization and measured it,” had proved there wasn’t any appreciable ionization—I’ve forgotten the velocity of the ions, 30 volts or something like that, maybe volts. There wasn’t one eight- thousandth of the ionization that you’d produce by electrons of the same energy. In general, Jack Tate would throw you in the ocean and say, “Now swim,” but not try (visibly) to help you. It was a terribly important lesson. I’ll never get over being grateful to that man, although then I felt awfully deserted, while Ernie was just steaming along, busy writing his thesis, I was just a feeble sap with notebooks that didn’t have anything but zeroes in them. It was smaller than I could measure, no matter what I did. Well, it turned out to be, if I dare say so, a perfectly good thesis. It happened to be true, and furthermore it gave me a feeling that really what you find out is up to you.
That’s a very interesting approach.
And I’ve never gotten over being grateful to Jack Tate. Even when I bellowed for help—I said, “I’m drowning”—he said, “Go ahead and drown or swim to shore. You’re on your own,” He just told me off, pretty much calmly like that, I’m sure it must have hurt him, but he didn’t yield, and it was two days before I came to him and said, “Well, would you accept a thesis if I proved that it’s less than so—and—so much?” He said, “Well, yes. That’s new, isn’t it?” He said, “I thought it was day before yesterday, but you didn’t seem to think it was worth anything. Just write it up.” Those were great days. Well, that’s how I got interested in physics. It grew out of early exposure, let me say it, to Hugo Gernsbach, to popularized writing about what they called “wireless” in those days. Modern Electrics and Electrical Experimenter: I always looked down my nose at these things; they seemed terribly trashy and so on. Nevertheless, it showed pictures, and it gave you an address to which you could send in just a few dollars and buy some parts to work with.
It’s interesting that in the same small town both you and Ernest Lawrence at about the same time got interested in this.
Well, I think that just came from this Scout experience.
Had you known him before? How did you meet him?
We were born six weeks apart across the street from each other, and we grew up that way, although when his father took a job as state superintendent of education or something, they were away for two or three years when Ernie and I were 10 or 11 years old. They were away at Aberdeen or Pierre, then they came back again. In and out, more than half of our boyhood essentially was spent together. And these critical experiences were along in the age group of seventh to tenth grade. That was when our interests developed. They created the yearning, and after that if just made you feel very good when you could learn something about these things that previously you hadn’t understood. My brother had bought me a book by J. Zenneck, (Munich) Wireless Telegraphy, when I was trying to help him sell Fuller brushes one summer. This must have been 1914 or ‘15. Let’s see, I was a high school freshman—it must have been about 1915. This book assumed you had a knowledge of calculus. Well, I didn’t know what calculus was. My brother had had calculus, but he didn’t tell me much. He just bought me the book and brought it home. I had said, “I want to get a real book on wireless and learn all about it.” Boy, I did my best in the first chapter of that, but I had written out by that time about five pages of things I didn’t understand, and so postponed study until I could be more grown up and qualified. Well, these are reminiscences.
They’re important. These influences may have determined your style of research in some sense, too.
Could have; could have indeed.
However, you mentioned that you had already applied to Princeton before you received your master’s. What made you apply, and how did one go about writing for a position as instructor at that time?
Well, there weren’t any graduate fellowships, you see. You had to earn your way by doing something. At Minnesota, for example, they had teaching fellowships. We graded the classes, and we took charge of laboratory sections and so on. We handled quiz sections, and also there were kind of tutoring sessions, where students were allowed to come and bring up questions which they didn’t understand. And we young teaching fellows were just supposed to be there and answer their questions——this kind of thing. So I’d been a teaching fellow for two years, starting even before I had my bachelor’s degree. Old Professor Henry Erikson said, “Don’t tell anybody you haven’t got your bachelor’s degree. But we know you know the stuff, so you can go ahead and have this fellowship.” They paid $650 a year at that time.
Where did the funds come from?
From the state indirectly then?
From the state appropriations directly. There were no other funds. That’s what enabled me to stay in, couldn’t have been there for my senior year except for this teaching fellowship. Well, they knew this, so I had two years as a teaching fellow, stayed on and took my bachelor’s degree in engineering to keep my feet on the ground. That’s what I said: “I want to study physics, but I think I better be sure I’m practical enough to know reality.” So I took an engineering degree, doing as few engineering courses as they would permit. Finally, my last two terms they insisted I do machine design, because they wouldn’t graduate an engineer who’d never finished this course in machine design, so I did that. But mostly I did graduate course work in physics and took all the electives they would permit. You had a feeling at the time of being pretty provincial if you were only at Minnesota—out in the sticks, so to speak. So instead of staying there to go ahead for a Ph.D.— (there were people with us who had come there from the East to take their Ph.D.’s; it was a perfectly good place)— I wanted to be sure that I knew what the rest of the world was like. So I asked where to apply. I think Tate was probably the one that said, “Well, apply to Karl Compton. In fact, he’s going to be in Minneapolis this summer, because he’s going to marry the daughter of our professor of Greek, Hutchinson,” which he did. So I saw him at Professor Hutchinson’s house as part of my application to come, and Compton gave me this instructorship. It paid $1800 a year—a lot of money. Harry Smythe had vacated it for a year or two while he went abroad, but then he wanted to come back, so that meant he had to get his instructorship back. Along in February or so, Compton lamely said, “Can you find another post some place, because this post won’t be available next year?” So I tried Hopkins and went down there. I was an instructor there for two years.
At Princeton you didn’t pursue any further graduate work?
I wasn’t a graduate student because I was an instructor. I wasn’t registered as a candidate for a degree, but, sure, I attended two or three courses. I studied with E. P. Adams and studied with Karl Compton, of course. What else did I do? Audited a couple of courses. But mostly I was doing research in the basement, again on acceleration of positive ions and electrons, Karl Compton was busy measuring ionization potentials by kicks in the curve of production of ions, and we had grids and so on. My big problem, as he repeatedly pointed out, were these ground joints with wax seals. You’d get small traces of wax vapor on your grids, and they’d build up charges and falsify your voltages. This was the big battle at that time. You had to outgas everything to get rid of these slightly insulating layers on the grids. Then I went down to Hopkins. The summer after I took my master’s degree—that thesis went through all right—I stayed on at Minnesota and did some library study and so on. Gregory Breit was coming as an associate professor the next autumn at Minnesota, 1923; so he was there during the summer, and I was in the lab every day, and he was in the lab every day. We used to go running around the athletic track together, and he got to know me. In fact, I was working that summer, come to think of it, on trying to detect very short waves. I wanted to measure things down in the region well below a meter. And we had some surplus Army tubes—J tubes and E tubes. The E tubes—these were Western Electric tubes-—have widely-spaced grids, low internal capacity; and I took the bases off, minimized the capacity to see how high in frequency we could go, and got waves on wires and measured them and so on. Breit had watched me doing these experiments. In fact, at Minnesota—I don’t know where it came from, but I think it came from my earlier experiences in South Dakota—I even announced that I was only interested in going to extremes of everything: extremes of temperature, extremes of frequency, extremes of voltage, extremes of distance, extremes of pressure, and so on. This is the way you learn about things—carry it to some kind of an extreme. Then you can find out what the limitations are. So this was part of that “extremes” business—- trying to see how high a frequency you could make with any available tube. When Breit got here at Carnegie, in 1924, I had been to Princeton and a year at the Hopkins. Early in my second year at the Hopkins, Breit called me up. He said, “Can you come down? I want to see if you receive short waves up there in Baltimore.” So I said, “Okay, I’ll come down.” So I came down here, and we had a talk. He said, “We ought to measure the Heaviside layer up overhead, because I think that’s where the seat of all these magnetic variations is. Here they have been monkeying around for 50 years with magnetic variations in observatories and so on, but nobody had done anything about the seat of the currents. It must be up there where the radio layer is.” He then said, “I want to put up a big, deep parabola out here on the Department’s lawn and maybe we can make 50-centimeter waves. We’ll send them up, and you can receive them in Baltimore.” I said, “Well, hold on a minute. It was a heck of a job to try to receive them across a room at Minnesota. I don’t know what the intensity will be. How many kilowatts can you put out?” Well, we didn’t know, but it was worth a try. It kind of scared me, so we went off to the Columbia Bakery here for supper, and I said, “Gregory, there’s another approach to this business,” Let’s see now. I’m getting ahead of my story. I didn’t do that until we had a formal discussion here. They had arranged a meeting. He gave me a glimmering of the notion first, and a week later they had a meeting upstairs in the library here, to which he had brought Dr. Cohen and Dr. Austin. They were in the radio section at the Bureau of Standards, the Austin-Cohen formula people. Also there were A. H. Taylor and E. O. Hulburt from the Naval Research Lab and two or three other people. Dr. Bauer (Director of the DTM) had called this meeting to find out if it was justified to spend a couple of thousand dollars to put up this parabola that Breit had talked about. Well, in the middle of this meeting—this is the first time they really asked me if I would be willing to set the receiver in Baltimore up there at the Hopkins, and by that time had thought over this whole thing—I said, “No, there’s another way. By all means, gentlemen, vote this $2000. You can’t do anything unless you can buy some equipment and have some money to spend.”
They were voting their own funds.
Yes, just advising the Director here that it was a wise expenditure. I don’t know why he was so hesitant. But anyway the amount concerned was $2000. I said, “Now, go ahead and vote this $2000, and assume that I’ll be a partner somehow in this. But I don’t want you to think that I’ve promised to receive these very short waves in Baltimore, because I’m not sure that anybody can do that. But I’d like to suggest that Breit and I will try to get some clue to the electrical state of the upper atmosphere. The other way to do it is by echoes. Give us the privilege with this $2000 to try some other method if this very short wave reflection looks too difficult.” They voted the $2000 and recommended that we should do whatever we could. Breit and I then went off to dinner at the Columbia Bakery here, which was a supper place near Chevy Chase Circle at that time, and in the middle of our discussions he said, “Do you know that KDKA has very poor modulations when you get out about 100 to 150 miles away from the station. You get out 400 miles and you can hear it pretty well—-the music is fine. And close in, out to 30 miles, it’s pretty good. But out around 100 miles, there seems to be interference,” So we calculated what the time delay would be for something going up to the hypothetical Heaviside layer and the direct wave, and it comes out to be of the order of 1000 cycles. So that would explain why the modulation, which ought to be a property of the signal that goes out, can be bad at some intervening zone. So we said, “That must prove there are two paths. It doesn’t prove that they move around, but it isn’t always bad at these places, so there aren’t always two waves.” So we thought, “Well, let’s see if we can do it from a spark transmitter.” I said, “How are you going to do that?” He said, “Oh, just record it with a cathode-ray oscillograph.” I said, “Oh, yes. Sure.” I didn’t see right away, but Breit was accustomed to this, too. Don’t forget that the cathode-ray oscillograph didn’t exist in these days, only the Duddell oscillograph, used as an electrica1 engineering instrument. So we came back from supper that night kind of figuring that this was what we would do instead of trying to build this parabola and having me try to receive these short waves up there in Baltimore. By the way, Professor Swann at Minnesota had spoken about the possibility of radio reflections from the upper atmosphere. Well, I’m getting into a long story here on the wrong subject.
It is the subject, according to your own definition of continuity in things.
Okay. Well, during that winter, of course, I was teaching in Baltimore, and would see him now and then. He set up a simple oscillograph. I guess he borrowed the first one from the Bureau of Standards and then had some money to buy some components. We couldn’t buy a whole instrument, no; but you could buy the galvanometer part, you see. So we had a little arc lamp, and he had bought one of these galvanometers, but their frequency was only, I think, 500 cycles-—the highest that you could get—and we needed a couple thousand cycles. Anyway we needed higher-frequency ones. So later that winter, both of us learned how— and in the course of the next several years, we grew quite expert at replacing the suspensions. We bought the little mirrors or made them, and we bought very fine tungsten wire, and we restrung our own up to 15,000 cycles. It took lots of milliamps to drive them, but we could make high-frequency oscillographs this way. Well, he looked at signals from various transmitters. Actually, they weren’t spark transmitters. They were keyed transmissions, but you could never be sure that the key wasn’t arcing a little bit, you see, and so you’d see these apparent kind of echoes right afterwards, but you never could be quite sure that there wasn’t key chatter. Along the while these observations were being made, Appleton announced (these observations were made January, February, March, April 1925) in Nature (in March) that he’d gotten interference between these two continuous waves traveling. But we suspected there were more than two paths. The Appleton system works all right when you’ve got just two paths more or less equal in intensity. So we kept on being interested in really verifying these pulses, and they asked me to come here for the summer, which did in 1925. But we immediately went to work with Naval Research to key their transmitters down here to verify with one oscillograph at the station that there wasn’t any key chatter, that the on and off was really clean, while simultaneously on the same keying we looked at the signals received there at Chevy Chase, 13 miles away, and there was an echo. This was the only way to prove that it was really clean. By golly, it was true. And the separation, as I say, was 103 kilometers. We looked at the map, and the darned Blue Ridge is just about 100 kilometers away. So we thought, “Well, maybe we’re kidding ourselves.” It never changed. Each afternoon it would be the same. We knew that propagation changes a lot in twilight, but we couldn’t have the set because the U. S. Fleet was over in the Indian Ocean and it was used every evening at 5 p.m. for Fleet communications. But along late in August (we got these records all during June, July) I was about ready to go to Minnesota or maybe had already gone to Minnesota. My family was there, and had to go and, think, move my mother. No, went back to Hopkins that year. It was the first year I was at Hopkins, 1924, that he called me—yes, in the autumn of ‘24. And I was at Hopkins until June 1926. So it was in the late summer of ‘25, anyway, that we got the transmitter for one evening, and, sure enough, by 6 o’ clock it was clearly different, and by 8 o’clock it had gone way up and in fact then had disappeared. I don’t remember; there were some troubles. But it clearly wasn’t the Blue Ridge, Well, that was that. Then I was going over to Rutherford. I had made arrangements to apply for a national research fellowship, and there was some hope of getting it.
You were still at Hopkins then. Had you started to work on your dissertation?
Oh, yes. 8 was one of Joe Ames’ last students. He said, “Good golly, you couldn’t find a better thesis than this ionosphere work. Go ahead now and write it up.” So that became my thesis. You had to hunt up all the historical references and so on. Meanwhile I was teaching a full load and also taking final courses and looking with dread at these final exams.
Who was on your committee—do you recall?
Oh, Pfund and Mernihan in mathematics and Professor Morley. I did two minors at the Hopkins at that time, one in physical chemistry and one in mathematics. I had done my mathematics earlier—had done Fourier theories and function theory and so on-—under Dunham Jackson at Minnesota. They regarded this as enough preparation for a minor, so I had to go then to Morley. I went to his house, actually, because during those two winters we would go and sing English madrigals at Morley’s house.
Didn’t you have an interest in music earlier?
Oh, yes, very much. I almost went into music. There’s a long tale that hangs on that. My father died and so on. Anyway, I was suspicious of music because all you do is play on the emotions, and I wasn’t sure but that I would be a very lopsided person if I only played on my emotions. So I made the decision I would go ahead and learn science first.
Was this E. W. Morley?
Frank Morley. He was the father of Christopher Morley. Professor and Mrs. Morley—he was an Oxford mathematician—had a few of us down from the graduate school, and we would sing madrigals and drink cocoa and have doughnuts. Anyway, I faced the exam with considerable trepidation because I had forgotten a lot of mathematics in two years away from it, but he set me this question: “A couple of hundred years ago, Bach tempered the scale, I want you to invent a better scale.” I said, “Well, that’s a nice assignment, but, you know, I came down to get my assignment for my mathematics exam.” He said, “That is your mathematics exam. You go home and think about it,” Well, the logarithm of 2 divided by 12 is of course the spacing in Bach’s scale, and the problem was to find a better one, It turns out—I forget now; it’s in my archives here—it’s either 17 or 19 tones. It fits very well. All the major intervals are just pretty well represented. It becomes C, C#, C##, D, D#, D##, E, E#, F, F#, F##, G and then two sharps and so on. I even worked out a keyboard and so on. That was my minor in mathematics. Then I’d had a course in physical chemistry from Bichowski and Urey. They were young professors there my last year at Hopkins. They taught physical chemistry. Lewis and Randall, which is a real good, meaty text, was the text they used. It was kind of unintelligible at times, especially from Bichowski, Russell Bichowski. He was quite a guy. But Urey and Bichowski taught that course. I don’t remember—I think Bichowski sat on my thesis exam. However, I would have collapsed except that Joe Ames made sure that he kept the questions steered.
Who else in the Physics department was very active besides Ames?
Well, Pfund, of course, and R. W. Wood and Ames—they were the main ones. I did some mercury resonance radiation work up in the attic and burned my eyes with ultra-violet light, wore goggles, of course, but I was using two mercury arcs in order to get very intense and focus both of them. I forgot that it would go in behind the goggles. I thought I was going to lose my sight. I called R. W. Wood up about 4 o’clock one morning told him about it. I was really worried. He said, “Oh, relax, I’ve had it happen about five times. It sure is uncomfortable, but you won’t go blind.”
Before I let you continue with an account of the trip to Rutherford, let me ask another question about other students. Were there other students interested in the same sorts of things?
Well, not the same kinds of things. Very catholic interests. But there was an enormous contrast between the graduate school at Princeton and the graduate school at Hopkins. At Princeton there was more in the tradition of reverence for ancient learning and the capacity to reproduce what somebody had done. At the Hopkins they said, “Well, that is what a library is for. You can go look up anything you need to in the library.” The thing they treasured was if you had gumption enough to try to add one more stone to the pile. To try to go out and do something new wasn’t very much—forgive me for saying it—the characteristic at Princeton. At least that is what I sensed as a youngster there. Maybe I was buffaloed by the sheer weight of the brilliance around me—I don’t know. But, anyway, it was kind of discouraging, really, at Princeton. I wouldn’t have gone on and finished a Ph.D. there. But at Hopkins they didn’t worry about the risk of giving Ph.D.’s to kind of punk candidates. It was the ones that went on and did things that counted. They knew that if you were too rough on them, you killed their initiative. Sensing this, Hopkins suited me just fine. I was interested to be able to go ahead and do things. It gave me a sense of values, too, which has certainly guided me all my life, to emphasize the positive; don’t worry about the negative—just filter that out and throw it off, but emphasize the positive. I was down here off and on during that winter after the pulse-experiment work in the summer of ‘25, and John Fleming, who was assistant director (Bauer was in worse and worse health), said, “Why don’t you come down and join us?” Breit had asked them to make a place here for me. I said, “Oh, I want to go and do high-voltages with Rutherford. Somebody has got to make high-speed protons, artificial alpha particles. We’ve got to speed up these things, and there’s no reason why one can’t do it. We know that if you put a million volts on a charged particle you’ll get something that’s more or less equivalent to an alpha particle to probe the nucleus. Protons and electrons somehow are stuck together, and I want to study that.” “Well, can you do it in one year?” I said, “Of course not.” “Well, then, why don’t you come here because you don’t have to quit at the end of one year.” This was Fleming. “You mean to say,” I said, “that a post here at Carnegie is anything like a National Research Fellowship?” “Sure,” he said, “you can’t make a new department every time you want to try to do something fresh. You’ve got to build it within the structure that’s available.” But he said, “That high energy problem sounds fundamental to me.” After all, I had said I wanted to know where the laws of electricity and magnetism break down. “If you get real close together, they must fail, because this stuff sticks together in the nucleus. How come?” He said, “Well, you better think it over.” I said, “Well, if I can come on the same basis as a National Research Fellow, sure, I’ll come here.” He said, “Okay, it’s a deal,”
Would you have gone to England as a National Research Fellow?
If they had given me one. I had my application all ready to go in, and Joe Ames was backing it and—I’ve forgotten—Breit or various people I knew. I might have had a fair chance. A lot of my friends were getting them. That was what I had fully counted on. But by the end of that February Fleming had said, “Why don’t you come down here?” Twenty years later, when they made me Director here in 1946 I said, “I hate to give up my fellowship. I’ve been here on a National Research Fellow basis ever since 1926.”
But there was no prior work here on the nucleus?
Oh, no, no—none at all.
Where did you get started on it? You said you knew by 1926 that this was the next thing you wanted to do. What’s the origin of that interest, especially, as you put it, because it was an interest in nuclear forces? It was a rather specific interest.
Oh, I think it goes as far back as South Dakota. It goes to this business of “extremes.” There must be some breakdown of the laws if things can hold together. I had heard, of course, about the Rutherford experiments in 1919. He was already breaking things up. So when I was a sophomore and junior at Minnesota, the Rutherford nucleus and the nuclear atom, were well discussed by Zeleny and the others there. Alpha particles were high-velocity particles, and Rutherford used them to drive protons out of the nitrogen nucleus. The trouble was that Coolidge had never got more than 200,000 volts on a tube, and no other people ever did either. That was a real struggle, those first three years. The struggle was that we didn’t have any voltage source. We had to build Tesla coils here in order to have anything that would correspond to putting a high voltage on a vacuum tube.
Where else in this country would one have had a source?
Well, if we’d had a lot of money… As a matter of fact, I asked General Electric for bids, quotations, and they did quote $3- to $400,000. Listen, our first appropriation was $2500 for a high voltage machine (1932) even after we could guarantee them that we could get results.
I guess the advantage then of, say, Caltech, of Lauritsen’s set—up was that this existed.
I mean the high voltage.
Yes, the high voltage maybe existed first, guess that was in the electrical engineering department.
It was built by the electrical utilities to test insulating materials.
That’s what it was. And Lauritsen got support for attempting very high voltage X-rays. But we didn’t have any voltage source here. General Electric would cascade the voltages for us and building high-voltage transformers. The rectifiers would give some trouble, but GE was prepared to make a 500,000 volt source, but the quotations were very high. I don’t remember what they were. They were astronomical in those days for this Carnegie department.
Where did you get funds from then?
We didn’t get funds. We got a thousand dollars at a time to last six months or a year, you see, from John Fleming. And Breit and I then undertook to build Tesla coils, build something that would make a high voltage. So we built a big condenser here out of window glass, built it with our own hands—window glass and lead foil. And we got a power transformer. We made sparks and Tesla coil voltages, measured them, had to use oil for insulation. There were three long years of sad struggle there.
Those were the years from ‘26 or so?
Well, yes. By late 1928 I persuaded Fleming to go easy on the radio work. We had to spend part of our time doing radio pulses through 1928. But in 1929, I went to Fleming and said, “Listen, as long as we stay in this business, because we were the first ones, the Bureau of Standards—Dellinger and his men—aren’t going to use the pulse method because we’re the grand old men of the mountain or something. But if we tell them that we’re going to stop and invite them to go ahead, they will get a half a million dollars from Congress and really do a job of it. We can’t do it. This is a big investigation. We’ve got the whole sky and all of the frequency regions to cover. All we can do is scratch the surface with a thousand dollars a year and two men.” This was after we had done a number of quite important things: pulse-interference, for example, using the Doppler effect. Odd Dahl and I had set up, down at Naval Research a system where we would leak a little of the output of their continuously operating transmitter crystal into the receiver, to monitor the phase relation continuously and then watch the phase of the echo as it came down, and it would phase in and out and in and out and in and out. We could tell every time the total path changed by one wavelength, you see, up and down. It moved rapidly downward until noon and then was steady for about half an hour. The reflecting “layer” then would start going up again in the afternoon, shortly after noon, or maybe it was 2 p.m. Anyway, we did this echo-interference method—I guess that was what we called it. We did a number of interesting kinds of pioneer ionosphere experiments, but my advice was to clear out, in order to persuade the Bureau of Standards to use our pulse technique. We stayed out of it for two years, and then the Depression came along. In 1932, when the Bureau faced a huge cut in their budget, we asked Lloyd Berkner to come over here and join us. We then started up again on the pulse-radio program. Well, that was the radio echo business. Meanwhile, we did work part time here, from 1926 to ‘29, on the high voltage and part time on the radio. We had Odd Dahl with us. This is Dr. Odd Dahl now of Mickelson Institute in Bergen. He left us in 1936. He was Harald Sverdrup’s assistant on the Maud expedition with Roald Amundsen. In fact, he was the aviator. He was the first man to try to fly over the North Pole. He said, “It was kind of lucky. We didn’t have gas capacity enough to get back. We knew we could not fly much beyond the Pole. We were just going to land some place and walk out.”
But the plane was smashed up on takeoff, so they never did have to walk out. Roald Amundsen was in the plane. Well, Odd [Dahl] came here as our technical assistant from ‘26 through ‘36.
I noticed a whole series of papers in this period on the echo work with Hafstad and with Breit.
Hafstad was a student at Minnesota. As I finished my engineering degree in 1922, I wanted to have some practical experience, so I took a job with the Northwestern Bell Telephone Company as a night man at one of the automatic telephone exchanges. The fellow who taught me the ins and outs of that was Larry Hafstad, who had just recently finished high school. He had worked for some years in this, even when he went to high school. And he was a shark on trouble-shooting in this Strowger automatic telephone exchange. Well, we got to be good friends during those midnight hours. Our turn was from 8 p.m. till 4 a.m. or 5 a.m. In the course of the summer I was studying German and doing some mathematics or something. I talked to him about going to college, and he was intrigued with it. I told him what we did in college and what the courses were about and what physics is about. He decided he would do it. So he kept his job there at night, but he came to the University during the daytime. See, I had just finished and he had just started. He did this for four years. And when he finished I gave him a phone call from here at Carnegie. I said, “Larry, why don’t you come down here and work with us?” He said, “I’ll come in a minute,” and so he did.
Did he have his bachelor’s degree?
Yes. He had finished his bachelor’s degree in electrical engineering. Then persuaded him here to go on to Hopkins, so he took some courses. They had arrangements for teaching Johns Hopkins courses at the Bureau of Standards. Then he took a year off and went up to Hopkins and did a thesis. He used the FP-54 for studying the proton emissions from disintegrations by alpha particles. What was he disintegrating? I don’t remember. Nitrogen, I think. I’d have to look at his thesis. But there again I egged him on, and he took it. We were friends all through these years.
As early as 1928, you had a paper with Breit. The title was: “The Production and Application of High Voltages in the Laboratory.’ Was this describing the building of the Tesla coil set-up here?
What’s the paper in? I don’t recall.
The paper was in Nature.
I’d have to look at it. Yes, we had built Tesla coils and immersed them in oil and studied how to measure the voltage by typical induction pickups, actually by a capacity voltage divider. We tried putting these on vacuum tubes. We busted all the tubes we could borrow from the General Electric Company. We put them on once, and they would puncture. We discovered it was very hard to put more than 250,000 volts on a vacuum tube, and so we undertook to make our own vacuum tubes. We had a glass-blower here. We made them in all kinds of lengths and shapes and divided the electrodes. We made the Tesla coil about this diameter, 6 inches. We put the tube, about 4 inches in diameter, inside of it.
The tube was a series of bulbs with a series of electrodes, and we connected those to the wires of the Tesla coil to make sure that the voltage was distributed. And we could put a million volts on this tube, and it would stay dark. It would flash at first, but pretty soon it would stay dark. Our problem was how to measure this darned voltage, and we gradually got so that we could believe our measurements. Actually, it turned out they were correct. By 1931, you may remember, Hafstad and Dahl and I wrote a paper. I gave the paper up in Cleveland, and they gave us the AAAS prize for it, of all things. We showed pictures of artificially produced high-speed protons and beta rays and gamma rays, all of which, using standard radioactive measures like the cloud chamber and penetration through foils or through lead with gamma rays, showed that we had on our tubes voltages higher than a million volts, about a million and a quarter, from these Tesla coils. Then came kind of a fallow period. They didn’t have any money here to buy high-voltage equipment. We were hunting around for any other way of making a decent voltage, and we were kind of stalled, until the spring of ‘32. And don’t forget this was getting deeper and deeper into the Depression. In the spring of ‘32 Robert Van de Graaff came back from Oxford; we had known each other at Princeton.
I was still in touch with the Princeton gang. I used to go back and forth; had friends up there in the physics department and so on. And he stopped by here. I knew him before he went to Oxford. He said, “Merle, when I was over at Oxford and talking to Townsend, I asked him why they didn’t use the old-fashioned electro-static procedures to make a good voltage, just put up a round ball and charge it up. You ought to be able to go to a million volts.” I said, “Yeah, I know, but how? Of course a million volts sounds very interesting to me. How are you going to charge it?” He said, “Well, just run a belt into it.” I said, “Say . . .“ And I sat and calculated what the field strength would be in a meter sphere and then a 2-meter sphere, and I knew at General Electric—we had been there seeking ways of measuring these Tesla voltages—they had a 2-meter sphere they used for their spark gap, and I calculated that you could sure go to a million and a half volts with that thing before you’d get a breakdown at the surface; and even if it was a rather poor surface, you might get a million volts. I said, “Van, you go right back to Princeton and make the first one. I don’t want to steal your idea. We’re going to make one here just the minute you’ve made the first sample. We aren’t going to allow the first Van de Graaff machine to be made by Tuve. You go and make the first one.” So he went up there and made a little pair of 20 inch sphere to put on a desk. I kept phoning him. It was about three weeks or a month later. I said, “Okay, now we can go ahead and make one.” We made this six footer. We got the General Electric Company to make for us the two spinnings to make a 2-meter sphere. It cost several hundred dollars, and I guess that’s about all. We got $150 for some pulleys and a silk belt. Then Dahl and Hafstad and I fabricated this darned thing right here in the building.
We had to buy an insulating column, and we got a Textilite column from General Electric Company. As soon as Van had tried his machines out, we assembled this thing and tried it. And to measure the voltage, I adopted what Ross Gunn had been using at the Naval Research Lab in measuring some atmospheric electric effects, a generating volt meter he called it. It is simply an insulated sector with a grounded vane that goes in front of it. Alternately it can see the voltage and then it can’t see it and then it can and then it can’t. By measuring the AC voltage in this sector, you could measure a high DC voltage at a distance, you see. So we mounted that generating voltmeter off to one side and looked at this sphere. We couldn’t do this in the house because the roof wasn’t high enough. We did it out on the lawn. Gee whiz, it went over a million volts! These first tests took less than three hours. So then we hurried up and got one of our vacuum tubes, and the next day brought out the vacuum system—mercury pumps and everything— set it up on the lawn and put this tube up against the 2-meter sphere and pumped it out. Sure enough, it would stand the voltage all right.
But the voltage, by the generating meter, would go up to a million, a million and a quarter, 1.3 million, and then it would abruptly come down to 600,000. You’d hear, “Bzzzzzz,” around. And we discovered right away (or the day before) that this was due to bugs—beetles and flies of various kinds and lightning bugs. So we mounted a feather duster on the end of a fish pole, and we’d brush the sphere off and then the voltage would go right back up again, and maybe stay there 30 seconds or 50 seconds, and “Bzzzzzz,” come down again. Then we’d have to go and brush that bug off. But we were interested to know if the high DC would go on these tubes, and sure enough, they stood up to it. Well, we didn’t have any beam in this tube. The temptations to put a filament in and use electrons, but I vetoed that because I’d had a lot of auxiliary experience with high-voltage x-rays, and I said, “Nothing doing. We can’t do this without a lot of shielding.” So we bided our time. Then Fleming asked President Merriam for $2500. No, let’s see. That’s when he asked him for $7500 to build a shed for the high voltage work. Previously we had gotten $2500 for the total Van de Graaff machine.
By the way, what time period was this when Van de Graaff came back from England?
I don’t know just when he came back. I believe it was March, 1932. It could have been earlier. We had this 2-meter sphere up and running in June 1932.
Then you went through Fleming to President Merriam.
And he got $7500 to build this wooden building, and we built that in the summer of 1932.
Well, it’s an addition to our experiment building here, made to house this 2-meter Van de Graaff with a high enough ceiling so that we could conceivably get a million volts inside of the room where we put our high-voltage equipment.
Prior to that it was just these runs on the lawn?
That’s all, yes.
What did you do when you were through?
We took it down. We had to take it down. We couldn’t have rain on those glass pumps.
By the way, were there any photographs taken of that?
Oh, yes. I have photographs upstairs in the files. In fact, maybe some were published. Anyway, lacking the ability to have this building right away, I said, “Well, let’s make a smaller machine, so we can use it in the experiment building.” So we spent August and September 1932, making this smaller one, which had a 1-meter hemisphere at each end, and a 1-meter cylinder in between in which we installed a power source, a generator driven by a belt—a separate belt, then a 10,000 volt source to make positive ions and shoot them through a canal. We had previously made ion sources of this kind. While this was just being finished came Cockcroft and Walton’s announcement. There are many things not being told in sequence here. Let me say that Breit had told us all along that you wouldn’t necessarily have to go to 5 million volts to get into a nucleus. Gamow’s theory of barriers showed that you could tunnel through the barrier with a certain limited probability. By the way, later brought Gamow here, actually to GW University, when I learned on a visit that he made to the U. S., I suppose about 1933, that he would be interested to come. (He was then at Cambridge). I happened to be an adviser to Marvin, the president of GW, his graduate counsel or whatever they called it. So I called him up and tipped him off that here was a man who was sure to be one of the world-famous people because of his nuclear theory—”Why don’t you get him?” And he did. He authorized me to go after him, and then he had the dean make him an offer, and so we brought Gamow here. So we knew in 1932 that it should be possible to go through the potential barrier and enter the nucleus.
Did you first learn of it through Breit?
I think so. We used to have lots of contacts. Heisenberg was here, and Breit’s contacts were very wide. And don’t forget that there was all this yeast of the quantum theory. Heisenberg had been here; Schrodinger had been here before 1930.
Were they actually at the department? Did they visit here or in the country?
Well, I met Schrodinger first at the Hopkins, I guess. Let me see if I can remember when we started the theoretical physics conferences.
The fifth one was held in 1939, I think.
I don’t remember just when. You see, this was the yeast of physics, beginning about the summer of 1926, especially with Breit as a theoretical physicist. We would go walking here in Rock Creek Park and out in the country in Montgomery County, and he would tutor me in what the latest theory was. He was trying to understand it himself, so he would expound to me the latest discussions and what he was worried about. In this way I got a lot of information about the activities in theoretical physics—the matrix theory, Heisenberg, and how in the world it could mean this and mean that and what the limitations were, and then when Schrodinger came along, and deBroglie had some ideas. In these years from 1927 through ‘29, there were lots and lots of discussions. We had a seminar here once a week or once every two weeks up in our library with the Bureau of Standards people—Foote and Mohler and Ellett and Ruark and McNair and others. So these ideas were cooking around. We knew about Gamow even before he came over, but when he came over, it was to talk about his potential wells. I had met him on some visit or other. Also Edward Teller came about 1932. In fact, I guess I was the motive force in both cases, again because of my post as adviser to Marvin. They were put on the staff down there at George Washington University.
Did these discussions of theoretical physics enter much into your work at Hopkins?
Well, this was after I left the Hopkins.
I know that, but were you exposed to any of these while you were there? Were you familiar with the events of 1925, ‘26...?
Yes, they were just being discussed in seminars. They weren’t, fortunately, part of the course materials that you had to pass exams on. You know, the early stages of matrix theory by Heisenberg looked like pretty much a foreign language to anyone who was used to continuum mathematics. Yes, Karl Herzfeld was brought there by Ames about the autumn of 1925, I would guess. I remember Ames calling me in and asking me what I thought of him as a teacher. I felt flabbergasted to be asked for an opinion. Of course, I was an instructor, and perhaps it was all right; he knew that I had been listening to Herzfeld’s lecture course. And Herzfeld would talk about some of these ideas, mostly in seminars, not in his lectures.
Was it a journal club type of thing?
Yes, a journal club type of seminar, at the Hopkins.
An informal, regular meeting of the group?
Oh, yes. We had regular meetings. People were assigned… Ames was a great one on that. He would assign things. You had to give a doggoned thorough report, you know. That’s the way you earned your spurs over there at the Hopkins. Ames ran the journal club. He would read the titles and would say, “I want to know about this, I want to know about that,” And he’d assign them to various graduate students, and you had to bring in a report on four or five papers at once. So I had heard some of this modern quantum physics at the Hopkins, and considered myself lucky that it would not be included-—they told us that details of this would not be included as part of our doctor’s exams.
Was anybody there particularly excited about it? Was it a question of just being afraid of it?
Oh, no, it was just that it was so new that how in the world could you get it all into a form such that you could make a decent presentation in response to a question.
Would anyone there have been capable of...?
Professor Murnighan, in the math department, was the kind of man that followed that sort of thing.
But not Wood or Ames.
No, not Wood or Pfund. Ames some, yes, but he was by that time pretty much involved in running the University. He became provost the next year. He learned new subjects more by indirection, by spurring some young chap to get up on his feet and expound. That’s the way Ames taught, except for his own very polished lectures, which were on classical kinds of things. No, quantum physics emphasis really grew up four years after the summer of ‘26 by Breit being here. He left here about 1931, and went to New York University. But in the course of those years and with the yeast here in Washington, the connection with the Bureau of Standards—there were many discussions of theoretical physics. It was recognized by everybody that this wave mechanics was a real yeast. We didn’t know quite what to make of it. And when Dirac came along, of course that was even another dimension of uncertainty or vagueness.
Did these developments all seem to point to the probing of the nucleus as the next step or was that just your particular interpretation of it? In other words, did the whole group of people seem to move to nuclear physic as a result of this?
The theoretical people who were working on atomic and nuclear physics, yes.
Was Breit working on it, for example?
Oh, yes. He was mostly studying the papers first of Heisenberg and Pauli and so on and then Schrodinger, Jordan and deBroglie and others. Let me see if I can answer your question. There were a very few people really trying to do any nuclear physics, maybe half a dozen on this side of the Atlantic. You see, the experiments were with alpha particles, and one would use different isotopes of the radium sequence for the different lengths of particles; and the experiments were pretty much the kinds of things that Rutherford was doing in 1918 and 1919. Larry Hafstad, for example. We went up to Dr. Burnham at the Kelly Hospital in Baltimore and got a whole handful of radon tubes. Larry brought these down to the chemistry department of the Bureau of Standards and managed to get the radium—E out, the polonium. And then using polonium alpha particles, he studied disintegrations produced by polonium.
They’re fairly short range, 2 or 3 centimeters, for very low energies. So there weren’t so many protons, but you could identify the difference between a proton and an alpha particle. A proton not only had longer range but less ionization per centimeter path, and this was the trick that he and others used. His was the first use of an electrometer tube, the FP-54, in studying radioactive transformations. And this is what Bohr and Pauli and Heisenberg and Jordan and de Broglie and Schrodinger and a few others, mostly at Cambridge, were concerned with. But I don’t think there were many others, except a few individuals scattered among the European universities. I had interested Ernest Lawrence in nuclear disintegration in 1928 or ‘29 when he was at Yale. When he moved to Berkeley he stopped by here, and said, “Ernie, for goodness sake, why are you playing around with mechanical things—spinners and so on? Why don’t you go after a high-voltage machine of some kind? You’re going out there to Berkeley and maybe they’ve got money. We can’t get one. And go after the nucleus. It’s sure as shootin’ that somebody is going to get high-speed alpha particles or high-speed protons and find out what the laws are that govern the structure of the nucleus, how the devil that nucleus can stay together. It’s clear that Maxwell’s laws break down when you get down below 10-10 centimeters.” He told me that this really intrigued him. Although he was doing some photoelectric work out there at Berkeley, he kept pondering on this, how to get a machine. And he and Livingston sat in the library (there were three men—-Edlefsen was the third one) and discussed it all one evening, and that laid the foundation—when they realized in discussion together that the time was the same for going around regardless of the radius of the path. Then they tumbled to the cyclotron idea.
You mentioned that you said to him maybe he could get the money at Berkeley, although you were having difficulty here. And yet you were doing high-voltage work.
Oh, we felt very squeezed. Listen, to try to get a million volts for $l000—that’s crazy.
But you were doing it. When was this?
This was 1928 and 1929 when all we had was Tesla coils. It was 1932, right in the middle of a sentence, that I saw that, by gosh, the Van de Graaff notion would offer a cheap high-voltage thing. So I just chased him right back to Princeton and followed it up with phone calls and said, “Hurry up and get that thing made so we don’t rob your idea. I’m not going to be a thief. But we sure want to use it, Van.”
Did you have in mind in the Tesla coil work and in the subsequent development of the Van de Graaff, the deliberate use of this to accelerate artificially...?
Only that. That was the only reason for making it, the only reason, That’s what I told Fleming in 1926 when he asked me to come down here and help with some of the radio things, to go ahead and go after high voltages. I said I wanted to put a million volts on a vacuum tube in order to accelerate protons. That was 1926, February. But it was at that time an old idea for me.
And yet even at that time the motivation behind that was the idea of pushing things to the extreme so that you could study the nuclear forces.
Well, study the breakdown of the Maxwell forces, Maxwell’s laws. That’s specifically the way I said it at that time. Yes, I guess maybe we used the term nuclear forces then. But what in the world were the forces? What’s the nature of the forces that hold them together? Clearly there’s either an attraction when you get close, or else the electrons were in the nucleus somehow or other. How in the world you can get electrons in the nucleus wasn’t clear. There’s a real region of unknown physics there. So that was an old idea. I suppose it went back to Minnesota as far as I was concerned. Because I bought Rutherford’s book when I couldn’t afford it. I remember that—in Minnesota.
Rutherford, Chadwick, & Ellis, you mean?
No, this was an earlier book of his. I don’t remember what it was, but I was fascinated by radioactive substances, you see, and radioactivity.
Now, in 1932, in June, you said you got results. Just after that, there were two important things. One was the discovery of the neutron. The other was the work of Cockcroft and Walton?
Yes, I was saying that after we got this machine, the first 2-meter Van de Graaff, to work in June 1932, we didn’t have a building to put it into. Don’t forget that money was awfully tight—it took several months to get $7500 from Merriam, and then it took several months to build the building. We knew this was going to take all winter, so we started to build a smaller machine. We just about had this 1-meter unit ready to run, had actually run it, in fact, when the news broke in the newspapers that Cockcroft and Walton had disintegrated lithium. It wasn’t a week later that we were making observations. We had fabricated all this thing from June till October, and there it sat. We hadn’t turned it on to the targets. So we turned it on on simple targets, and, sure enough, alpha particles.
We had all our detection apparatus ready—everything. It was a few days… We not only found these copious particles emitted by lithium and by boron, but I was aware by that time—I don’t remember quite why—of the ubiquitousness of contamination. And I was hipped on the idea ... “After all, there’s borax in soap, borax every place. If there are these huge ratios between the probabilities of disintegration of light elements and heavier elements, I just don’t believe all that Cockcroft and Walton put out. Sure, the light elements, that’s clear.” But they had disintegrated everything up to gold, you know. I said, “I’m sure that part’s baloney.” So we carefully went through a bunch of elements—foils and so on-and we measured the ranges, and they turned out to be boron. Most of them were boron. We found boron contamination every place.
Where did you publish those results? Was that in Physical Review?
Yes, although I was a funny guy on publication, always have been. I think I’ve had this notion about the development of “the generic mind,” and my strong prejudice against subscribing to the genius theory goes way back almost to undergraduate days, think. So we published rather little on the Heaviside layer, too. Even though we would find all kinds of things, I would say, “Well, that’s going to be there next year and the year after. Why in the world publish this stuff that we know is so incomplete and uncertain? Let’s wait and measure it right.” The same way with these contaminations.
What about in a case where you were criticizing or correcting or refining someone else’s results?
Yes, that had me over a barrel. I didn’t like to publish it. I may have made an abstract at one time to try to quietly say that a great deal of these things were attributable to contamination. But that’s a negative result, and I never like to call attention to negative results. It was pretty hard to be ahead of the others in Cambridge and Berkeley on positive results, because of course they were starting to harvest at a great rate.
Who were “the others”?
Well, Cockcroft and Walton and Lawrence’s men primarily. In Cambridge they had Rutherford and his whole Cavendish lab behind them, pouring on the coal, measuring everything day and night. Pretty soon, Ernest was in the same thing, and they ran day and night—students and everybody. Actually, everything that was measured here, I had to do—either Hafstad or I, I was too cautious.
How about Lauritsen at Caltech?
That came along shortly afterward, too. I went out to visit them in ’34. By that time they had made a lot of different disintegrations.
How about the discovery of the neutron? How did you hear about that and what was the reaction?
Oh, in the newspapers. Our reaction was one of great relief. At last there’s some sense to this nucleus, and how this could have escaped us, that and artificial radioactivity, too ... We had artificially radioactive things right in our hands all the time, and we hadn’t measured them. We felt like chumps on that one. But the neutron—that’s elusive enough so we didn’t feel so badly about that ... But on artificial radioactivity, I really did miss the boat. In fact, so many things happened that we just missed that I was chagrined all the time for a year and a half.
What, for example, were they? That’s interesting.
Well, in the first place, we had proposed the experiment years before. We had slowly worked up to it. We were all set with the second Van de Graaff machine in order to do the first disintegrations when they beat us to it by not more than two weeks because we were all set to do lithium, do the light elements, as pointed out to us by Breit in 1930. This was part of our proposal to Fleming and Merriam in 1930 for a high voltage machine to bombard the light elements with protons. In 1932 we had the proton source ready. That was a separate job to work out, you know. Nobody had made any such thing as a beam proton source. So we worked that out. We had the Van de Graaff, the second one, all built-tubes, everything, targets, detection apparatus, shields—golly. And then we were tardy because we went home to sleep at night instead of ants in our pants... Well, that’s one. Then came artificial radioactivity. That was the second one. There I felt really ashamed, that we hadn’t just looked for electrons from the targets we’d been bombarding.
Then the neutron came along six, eight months later, and that was kind of a bomb because it made the whole of nuclear physics much less mysterious, a much more acceptable part of nature. So the fact that Chadwick found it. Well, we were kind of glad that it was the British. The French have a way of rubbing it in, somehow, when they make a discovery.
Were you in contact through correspondence with people at the Cavendish during this early period?
Not really. I don’t remember that I even wrote. I may have written a letter to Cockcroft—of course we got to know him very well later.
He was here in 1933, I guess.
Yes, but would he look and see if much of these heavier-element disintegrations were really due to lithium and boron contamination? But then we looked at carbon and that had some groups of its own, and we were trying to make gas targets; that was harder.
At the time when you were ready to put the second Van de Graaff into operation, were you aware of what Cockcroft and Walton had been trying to do?
No, I don’t think so. No, I don’t think we knew.
And you never knew except through the newspapers?
When they got the disintegration, yes.
Was that through the newspaper or the journals?
No, the newspapers.
And then how long after it...?
I’d have to look at our notebooks, but I suppose it may have been five days.
I don’t mean your work. I mean the journal article of their report.
Oh, Nature came out very quickly. I think it was in 10 days, two weeks.
I see. So it was pretty close. In 1932—I just want to skip for a minute—there was the International Electrical Congress in Paris, Did anyone from here go?
I guess there was some report of the work here that was given.
I contributed a requested paper, which they translated into French. Was that ‘32 or was that ‘33?
Well, the bibliography shows ‘32. I‘m basing it on that.
I remember making a manuscript.
That’s not a major point. If you had gone, I would have been interested in knowing something of what was discussed. In 1932, when the discovery of the neutron began to make nuclear physics intelligible, as you indicated, did this have any effect on people’s consciousness of nuclear physics being a good field?
Oh, the minute Cockcroft and Walton made their disintegrations, then it began to be quite clear that this was going to be a very fruitful game. And of course the cyclotron came in right there, too. I think Ernest was doing artificial radioactivity within two days, or three days anyway after the telegram arrived. When was the artificial radioactivity? Can you remind me?
Well, there was some work leading to it. 1934 is the date that attribute to a certain variation of it. It was early work by Curie-Joliot which led to the Chadwick work on the neutron. That was ‘32.
The real discovery of the induced radioactivity wasn’t two years after Cockcroft-Walton, but was only a few months later. It was ‘33, I think. That was pretty quickly followed up. I would say that among the theoretical physics people and people who were in the habit of worrying about theoretical problems, reading those papers and thinking about them— not only the creative theoretical physicists—there was a lot of yeast going by reason of the Heisenberg-Schrodinger-Bohr-Pauli-deBroglie yeast that had been going on for six years, much of it centered around nuclear disintegrations produced by radioactive particles. The ground was well prepared for a great many people to be interested in doing these things by artificial voltage sources. Of course Karl Compton then immediately set about making the big Van de Graaff high—voltage machine for Round Hill, that pair of big ones, and that was going to be big nuclear physics and so on. Various people had big dreams and big money requests.
Ernest was the one who started with a small cyclotron and began pyramiding that to bigger and bigger sizes, We were happy to have something that would work above a million volts so that we could do things. During ‘32, ‘33, and ‘34, I decided that the whole atomic table could be surveyed by the university people, with all their graduate students. They could just assign one graduate student to each element and say, “Here, go ahead and study it.” That seemed like kind of an inappropriate thing to do with just two people here. So pretty much I kept our thing steered towards the original goal:
“Let’s measure billiard ball collisions. Let’s repeat the old Rutherford alpha-particle scattering experiments.” That meant that we had to measure the voltages. This was quite a task, and we got Ray Herb here for a summer appointment in the summer of ‘34, I think. We built with our own hands, using carbon resistors (we tried wire ones but they were too expensive) but with condensers between them; in other words, a series of flat plates. We’d have 100-megohms here and then flat plate, 100-megohms, flat plate, and so on.
We made a volt meter which would measure by the current what the voltage was. We were very pleased to discover that this unit confirmed our generating volt meter measurements. By this time we had discovered the resonance reactions in lithium and fluorine—those were the two that we had picked for many steps in the voltage calibration curve—and we then calibrated our voltage at the onset of these resonance reactions, which were convenient calibration points later for any kind of voltage indicator. You see, we really had to have absolute voltages before we could do the classical billiard ball scattering experiment. I knew that we just couldn’t do proton-proton by guessing at the voltages within 10 percent.
And finally we set about to just scatter protons on protons, and that was 1935 and ‘36. And, by golly, up to about 700 kilovolts, it was pretty classical, and then abruptly, from 900 thousand to a million volts, you get evidence of a really marked attractive force. I was surprised that we were fortunate enough to do this first, after all the heat that had been going on for four years in all these other labs, everybody rushing as hard as they could to measure everything and get it all in the literature—a lot of it sloppy, you know. I had been unhappy about that. But the proton-proton scattering was a very satisfying experiment. We had Amaldi here the summer of ’35. He had come to a theoretical meeting at Michigan or something. I knew he was coming, so I asked him to spend the summer with us. We made a big tank of water about five feet in diameter, four feet deep, and had our high voltage beam target down in the middle of that, and measured neutron activation in the water; we used indium foils and so on. It was a very good lesson in picking up the techniques that he and Fermi and Rasetti had used in Italy.
I imagine he came here to pick up some techniques, too…
Well, he was very interested to use the high-voltage equipment, yes; and so that was a good trade.
I notice you did a paper with him that was published in 1937. I wondered how that came about. I guess that was as a result of the work.
Yes, Maybe it was ‘36 then that Amaldi was here.
We’ve talked with Segre and we have year by year who visited where, and so we can fill that in. [Amaldi visited the Carnegie Institution in 1936.]
Well, we have the DTM annual reports, and we can check things there.
I have many more things to cover. But in the few minutes remaining, I’d like to ask a specific question about the Washington conferences on theoretical physics. Do you know who was involved and how they came about?
There I should have refreshed my mind, especially by dates and so on. Let’s see. Breit maintained a connection with our group all through the years after he left here. I regarded him as our principal adviser on theoretical things, in spite of the fact we had Gamow and Teller here in town after 1934. Breit has always been generous and thoughtful, and he has the remarkable capacity, you see, to be really interested in numbers— not just in theoretical equations and so on, but he always reduced things to numbers that could be compared with somebody’s experiments. I’ll have to look up as to just how that first one got started, but I‘m sure that it was partly because Breit was associated with it. But I think that the opportunity really came about because Gamow and President Marvin at GW were interested to take a share in it, and this was something that would help build the Washington community as far as interest and connection with theoretical physics was concerned. So it’s something that I’m sure I cooked up with Gamow.
Do you remember who paid for it?
Yes, indeed we do. We each paid half. John Fleming got money from Carnegie, and I think there was a special earmarked item at the central administration (Carnegie) for scientific travel or scientific conferences or something. Anyway, it wasn’t part of the department’s budget. He always got special money enough to cover whatever the expense would be from President Merriam (later from President Bush) and President Marvin would give his guarantee that they would pay half the bill. So the accounting was done here to pay the people their expenses and so on and then divided in two and Marvin would send us a check. So this was a real joint activity between the two places, and of course this was done by our department for the Carnegie Institution as an Institution activity. In this way it wasn’t part of the department’s budget and didn’t have to be prepared for the year before.
But Gamow and I—and of course after Teller came, Teller would join in—decided what the topic would be and whom to invite. We were interested in fundamental physics. That’s what it was all about—fundamental theoretical physics as of the current date.
The new thing was that we wouldn’t require any reports, we wouldn’t require people to prepare papers, and it really was just to be an informal discussion between active people concerned with a particular subject. But it was specifically to be of some advantage to our Carnegie interests and to the GW interests. So we jointly selected the title and the people, and we were more privileged than others to attend. Although some of us, like myself, who weren’t qualified to be theoretical contributors, were still allowed to be part of the conference and listen and ask questions.
Did the topics vary from year to year?
Oh, yes. I would have to look up a list of them.
But would you pick a theme for a particular year and focus on that theme?
Yes. I suppose this is the one that you have references to there: Specifically we wanted to examine the problem of nuclear reactions as stellar energy sources inside of stars. That was one of them.
That’s the one that Bethe attended and when he came back worked out something on…
On the Pullman going back to Ithaca, he worked it out then as to what the carbon cycle would be. Then there was one that specifically asked for on the red shift. This was right after wartime. It was just after the war ended. So that’s a later one that may not even be in your list. In other words, could we have “tired light”...? Was this possible? The loss of energy by individual quantums.
What about the one on fission that’s so well-known? Had that been selected as a topic?
Oh, no. That came as a bomb shell in the middle of the first day, I guess. These would usually be Thursday, Friday, Saturday; and this was Thursday noon. And the telegram arrived at about 11:30. We have the records no doubt, the actual title of the conference; but Bohr and Fermi were both there. It was concerned with nuclear levels or something like that. It may have been on neutrons. But we were down there at GW that year, and remember sitting in that room, and somebody brought in a telegram from Frisch to Fermi, and he read it, and Bohr was sitting there. Bohr started to talk excitedly. It was a little hard to understand Bohr, you know. He talked as though his tongue was in the way. They were very excited. They started to talk about what it must be. They called them “splitters.” The telegram was simple. It was from Frisch. Meitner had brought the word to Copenhagen. It was either Meitner or Hahn who said: “The barium comes from the uranium.” That was the telegram.
Is that preserved?
I doubt it. Anyway it was a telegram personally to Fermi. It’s probably in his papers if it is preserved. Anyway, it didn’t say anything about fission or anything else, but that they are convinced that the barium comes from the uranium. So then the puzzle was to decode this. Fermi and Bohr decided in the first minute or two to take it at face value:
“It must mean that the barium is born from the uranium. How can this be?” And of course they were perfectly aware of the energy relationships and so on, and so they took a look at it. People had nuclear mass tables there and so on. In fact, I think Fermi carried enough in his head to say, “Well, if the energy deficit and mass deficit is such and such and such and such, sure.” And then: “It must be splitters. It must be like an amoeba.” And so they were talking about surface tension. Right there within 20 minutes of the arrival of this telegram, they were talking about how they could calculate surface energy for the nucleus and so on, I leaned over to Larry Hafstad. I said, “Larry, go out and put in a new filament.” We’d burned out a filament in the ion source that morning before we went down to the conference. “We must put in a new filament. Let’s run this experiment tonight.” Actually that was Thursday noon, and Hafstad and Heydenburg got our equipment working by the next day. They went out and put in a filament and pumped down so it was working, and we took a look at things that Friday. But Bohr and Fermi couldn’t come out on Friday. I think Bohr wasn’t feeling too well. But we said, “We’ve got splitters here. We’d like you to see them.”
They said, “Okay, we’ll come out first thing in the morning.”
So Saturday morning they came out. We’ve got pictures of that occasion upstairs here, too, and in the basement target room we showed them both in the cloud chamber these enormous long fat tracks of fission, and also the large ionization “kicks” on the cathode ray tube of the ionization chambers. So both Bohr and Fermi saw their first uranium fission right down in the basement target room here at DTM.
Lawrence Randolph Hafstad, “The Application of the FP—54 (Pliotron) to Atomic Disintegration Studies on Neutrons and on the Resonance Disintegration of Aluminum,” (PhD, Johns Hopkins, 1933).