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In footnotes or endnotes please cite AIP interviews like this:
Interview of James Chadwick by Charles Weiner on 1969 April 20,
Niels Bohr Library & Archives, American Institute of Physics,
College Park, MD USA,
For multiple citations, "AIP" is the preferred abbreviation for the location.
Family background; early interest in mathematics; physics at University of Manchester; Ernest Rutherford's influence; early research under Rutherford at Manchester; examination by Joseph J. Thomson for degree; recollections of associates at Manchester, including Niels Bohr; scholarship to Universität Berlin and work there with Hans Geiger; internment during World War I; scientific work at internment camp; return to Manchester; move with Rutherford to University of Cambridge; appointment as Assistant Director of Research at Cavendish Laboratory (ca. 1923); work with Rutherford on artificial disintegration; Rutherford's idea of the neutron; early experimental search for neutron; duties and experiences at the Cavendish Laboratory from 1919 to 1936; Rutherford's personality; Solvay conference of 1933; reasons for leaving Cambridge for University of Liverpool; initial plans, personnel and activities at Liverpool; cyclotron; award of Nobel Prize; encounter with Joliots, also in Stockholm for Prize in chemistry; influx of refugee theoreticians; work on the meson; changes effected by large machines; recollections of announcement of fission; World War II work; involvement with A-bomb project, Los Alamos Scientific Laboratory and General Leslie Groves; postwar considerations regarding international control of atomic energy; effect of Rutherford's death on Cavendish; return to Cambridge as Master of Gonville and Caius College; circumstances of resignation as Master; appraisal of personal satisfactions. Also prominently mentioned are: H. K. Anderson, John Anderson, Homi Bhabha, Patrick Maynard Stuart Blackett, Niels Henrik David Bohr, Paul Adrien Maurice Dirac, Albert Einstein, Charles D. Ellis, Walter M. Elsasser, Ralph Howard Fowler, Maurice Goldhaber, Otto Hahn, Walter Heitler, J. R. Holt, Ernest Orlando Lawrence, Douglas Lea, Lise Meitner, Stefan Meyer, Henry N. Moseley, Walther Nernst, Giuseppe Occhialini, Mark Oliphant, Maurice H. L. Pryce, Stanley Rolands, Heinrich Rubens, Joseph John Thomson, Merle Antony Tuve, Walke, H. C. Webster, Charles Thomson Rees Wilson; Department of Scientific and Industrial Research of Great Britain, Manchester Literary and Philosophical Society, Ministry of Aircraft Uranium Development Committee (Great Britain), Physikalische-Technische Reichsanstalt, Royal Society (Great Britain), University of Birmingham, University of Cambridge Cavendish Physical Society, and University of Liverpool.
Let's make a point of saying that today is Sunday, April 20th. We're resuming in the morning. This is our traditional morning session. I think that yesterday we had started talking about Liverpool with a general characterization of it. And it was just about the time you went to Liverpool that you received the Nobel Prize. I'd like to talk about that. From the beginning, had you thought when you had done the neutron work that this might be of Nobel Prize caliber, and that you would be, so to speak, in the running for the Prize?
Not particularly. No, it hadn't crossed my mind until I was showing the experiments to Leonard Jones, who was a theoretical physicist more on the classical side than quantum mechanics. But he was an old friend, and he just happened to drop round to see me, and I told him the position. By that time, you see, I was pretty convinced that this was the neutron. I told him so, and I remember his saying, "Ah, but this means the Nobel Prize." Well, it had never crossed my mind, and it didn't later really. It's somewhat difficult to express my feelings about those things. The award of a Prize, it seems to me, to be not so much a question of luck but a question of being there at the right time. Also, they have rules which I don't fully understand. There are men who in my opinion should have been awarded the Nobel Prize in some cases much earlier than they were — in some cases where they were awarded it, they were, in my opinion, a little late in getting it. I mentioned one yesterday — Charles Sherrington. It was a long time after he had done his work, and he was recognized as something quite exceptional, and so he was. I didn't know that I was being proposed. Well, you're not supposed to know, but I didn't know; and the first intimation I had: I think it was that I was in the laboratory, and I had a message that there was a telegram from Sweden. Then a kind of vague suspicion crossed my mind. And the same evening I think was, Rutherford rang up to congratulate me. No, that kind of thing — it may have been rather stupid of me — it didn't seem to concern me very much. It was very welcome, and more than that, but I hadn't thought very much about it before it happened.
What was your reaction then when you did get the notice?
Well, of course, naturally extremely pleased, but I don't think I can say much more than that.
Then, of course, you had to prepare an address upon receiving the prize.
Yes, that wasn't very difficult. At the same time it wasn't very easy, because I had nothing new to say at that moment. That was the least of my troubles. Most of them were trying to do the right thing while I was in Sweden. It wasn't so very easy because I didn't know what was expected of me, and I was given a guide who was supposed to tell me, to look after me generally and to see that I got to the places at the right moment, to tell me what was about to happen. He was a Count von Tolstoy, some relative of the famous Tolstoy. But he wasn't very good. To give you one example: I did manage to turn up at the right places at the right time more or less. But at the conclusion of what I may call the festivities, there was a very big dinner at which the crown prince presided. His wife was the sister of Mountbatten. I sat next to her. And I had asked Tolstoy if I was supposed to do anything, to make a speech. He said, "Oh, no. You might just say thank you — nothing formal about it." But there (it) was, and I was suddenly called upon to make a speech at the gathering. Well, I was in a dreadful pickle. I was extremely nervous by that time, having gathered that speeches were going to be made, and not the faintest idea what to say. I mumbled a few words and left it at that. I could have said something much more to the point if I had know that I was expected to make a speech — not a long one but something more or less appropriate to the occasion.
Speeches were given by the other recipients in the other fields as well?
Yes. I only remember one. I think he was a physiologist, a German, whose name I have forgotten. And that warned me that I was expected to say something. He had been properly prepared, and he had a good speech ready which he read out. It was then that I realized that I should have to do something of the same kind for which I wasn't prepared. There were several other things of that kind which happened. For example, I didn't know that a deputation was awaiting me on the railway station at Stockholm. If I had known, I should have looked out for them. But all I did was to take a taxi to the hotel. They missed me completely. They thought I had got lost somewhere.
It probably caused more difficulties for them.
Well, Siegbahn, whom I knew already, and his wife, were very kind; and we managed to turn up at the right time in the right kinds of dress.
The Joliots were there for the prize in chemistry. Did you have much contact with them?
Oh, yes, we had occasional meals together when we weren't going to some formal dinner, very happy meals together. I was rather fond of Frederick Joliot and to some degree Irene Curie, who was rather different. But I think I can say we were very friendly. When I say we had meals together on occasion, it may have been only once or twice perhaps during the proceedings, but I do remember one occasion very well indeed, because it was quite happy. And I remember his address at the meeting, which was very good. There was nothing very much of scientific interest in it, but it was done with — what shall I say? — panache. He was a great actor. He liked that kind of thing, and he did it very well. He would have been a very good actor. Irene would not have done things of that kind because it was not in her nature. She was much more reserved. Indeed it was a little difficult to know her properly. She might have said the same thing about me. But on the whole we got along very well.
Had you known them before this meeting in Stockholm?
I had known Irene Curie, yes. I should say she had been at this conference that I mentioned.
‘27 or ‘28. I'm not sure whether she had visited the Cavendish after that or not, but I have a very vivid memory of her coming to lunch at my house, to the consternation of our domestic, because she had the habit of breaking up her bread, and some pieces she would put in her mouth and some she would throw over her shoulder.
Really? As a nervous habit you mean?
I suppose it was, yes. Oh, I knew her reasonably well.
And Joliot? Had you met him?
I can't remember.
It could have been at that London conference in 1934 or the Solvay. I don't know whether he was at the Solvay Conference.
Oh, yes, of course, he was. Yes, of course, I met him there. They were both there.
This dinner that you referred to as a happy occasion, was this a small private group?
Oh, it was just us.
The four of us, yes. We were in the same hotel, you see.
I just wanted to cover that and get your reactions to it. The ceremony itself went off without any special hitches?
Well, it wasn't exactly a hitch. Why do you ask that question?
Because of the nature of those rituals, sometimes I think there can be humorous things involved, although I don't know of any in this case.
Well, there was one due to a piece of what I might almost call stupidity on my part. Speeches were made about my work, and then the Crown Prince presented me with — shall I call it? — a book in which was inscribed the notification of the award. Inside the book was a check. But I didn't know that, and it fell out. As I was leaving, I had to pick up this piece of paper in full view of the audience, not knowing what it was. That caused a certain amusement, but I had not been told that that would happen. It was, I suppose, due to nervousness, but it loosened inside the book, which I must have somewhere but I don't know where. At the moment I don't know where I put it.
Then I guess there was the normal rounds of formal dinners and balls and so forth.
Oh, yes. Well, the Swedes are a very hospitable people, and they were very kind. The dinners were very large and extremely formal, but quite pleasant. It would have been so much easier if I had know what I was supposed to do and what was going to happen, but I never knew from one moment to the next. And Tolstoy would suddenly say, "We now have to be at such-and-such a place." Later on I was able to warn one or two people what was expected of them in case they were told. Actually the Joliots got into a little bit of trouble. Whether they had known or not, I don't know; but there was a little trouble. When I say trouble, I mean they did not do what was expected of them, and I think they had not been properly informed.
You mean a protocol type of thing?
Yes, very much, which no doubt had been laid down for many years and to which the Swedes were accustomed, and I presume it was part of our guide's duty to tell us this, you see. However, this was quite a trivial matter.
When you returned home, well, even before you went, I'm sure the letters of congratulations kept coming in.
Oh, I have no doubt they did, but I can't remember.
Did it affect things at Liverpool? Did it make it easier, for example, to develop your plans for the physics program and to obtain resources?
I suppose it may have done, but I wasn't particularly conscious of that, because I did not have any difficulties within the facilities that the University could provide. You see, I was able to get extra stuff, not much but a little. I was able, for example, to get the University to found a readership in theoretical physics, which was a great help. I thought that was very necessary. And I remember the applications that I had. Three (there may have been others) were quite outstanding. There was Heitler, who was then in Bristol; Bhabha, whom I knew already — he was a member of my College at Gonville and Caius, and I knew him in Cambridge —; and Morris Pryce. Well, it was a very difficult choice. I knew that it was no use thinking about Heitler, because an appointment of a German would not have been agreeable to some of the people in the University, particularly to some of the business people. Bhabha came up to see me. I would very much have liked Bhabha to come, but I thought he was too good. Well, you see, some teaching had to be done, and the quality of our students was not the quality of the students in Cambridge, and I thought that much of it would be drudgery to a man like Bhabha, who was a most exceptional man. He was a painter and a poet and had extremely wide interests — not merely interests but far more than that — and I didn't feel that however much I like him it was fair. And so it came to Morris Pryce, whom I knew. I had known him in Cambridge when he worked under Ralph Fowler.
What year was this? Chadwick I can't remember. It may have been just before the war. It was indeed; it was before the war, because he was there in 1939.
And this was the first theoretical physicist in the department — I mean during your period there?
During any period. There had been a man whose interests were on the theoretical side, a rather senior man called James Rice. But he did not have the training which was necessary for such a post. But he had died, I think, before Pryce came. I don't think he lived much more than a year after I got to Liverpool.
What was the general situation in regard to theoretical physicists at English universities? We talked a little about the Cavendish.
Oh, there were very few.
Did they tend to be clustered at a certain place?
Well, you see, in the early days — when I say the early days, 1919 — I can only remember one definite post in the whole country. That was at Manchester, where the readership had been founded by Schuster and the stipend paid by his own pocket — for some time anyhow — and that was the post that Bohr had just before the war; 1914 he came back. I remember very well an occasion on which I had come back from Germany for a few days and visited the laboratory and met Margrethe Bohr for the first time. They had been married only a few months then. The first man that was appointed, as far as I remember was Bateman, who went to California.
Did he? I'd forgotten. It was a long time ago. Then he was succeeded by Charles Darwin. And the next one would I suppose have been Niels Bohr. I don't know of any others in the whole country, but then of course I didn't know everything that was happening.
By the late ‘30, the period that we were talking about, you made this appointment at Liverpool. Had the situation changed by that time at other universities? Had they been adding theoretical physicists?
I expect so, because they were then available, chiefly due to the efforts of Ralph Fowler. He encouraged the mathematical students to go into physics, those who had an interest, any kind of interest in it. It was almost entirely due to him.
With some of the refugees from Germany and from countries in similar situations, did the situation change in England? You mentioned Heitler, for example, as a theorist. Then Peierls came; Bethe came. Some people, of course, came just for a short time. But how did that affect the situation?
Well, it helped a great deal, because there were many, but they were very able people. But the difficulty was to find a post for them. It was not easy. You could find some temporary assistance from what was then called the Academic Assistance Council, but to find a permanent post was not easy at all. That I think was why Bethe went to the United States. I for one should have been very anxious to keep them all. Max Born got a chair in Edinburgh. But Peierls, I don't quite remember what did happen to him.
He first went to Manchester. And then I don't know whether he went from there to Bristol — I'm not sure. But eventually, after a series of temporary posts, he got settled.
He settled in Birmingham.
He went from Manchester to Birmingham (with a stay in Cambridge in between).
I don't remember exactly what happened in those days.
When you say there weren't enough posts, what did this mean for the students of the Cavendish laboratory, people who had come through the laboratory as research students and who had gotten their degrees? Did they have difficulties in finding suitable positions?
No particularly. You see, immediately after the degree some would get grants from the DSIR which were just sufficient to keep them. Some of them would do a little demonstrating in the laboratory, which brought in a little amount of money, but part of that would be deducted from their grant if they were getting a grant from the DSIR. But the grants were made, I think, for two years and could be extended to three. Again I forget the details. But then, of course, they went to junior posts in universities or into industry — some to teaching, but very few, though there were some. There wasn't the same difficulty about them as there would be about these German refugees. They were younger, and it was much easier to find a junior post, and in any case the junior posts were always becoming vacant as people moved up and moved out of the universities through age. But in the case of the refugees a junior post would have been quite unsuitable. And, of course, there were other difficulties naturally. As I mentioned about Heitler, it wouldn't have been at all easy to get him accepted. I expect it could have been done, but it wouldn't have been easy, and I wasn't prepared to run the risk of having trouble or having him in a disagreeable position, which might have come to.
Would it have been more difficult in Liverpool than in other cities?
I don't know. It would certainly have been more difficult in Liverpool than in Manchester. Manchester had had for many years a small but important German group, of German descent, who were in business in Manchester. They were a very important group.
As a matter of fact, there was in Manchester, I recall a sort of a local academic assistance council which was formed, which provided funds.
I didn't know that, and I haven't now got a book written by Beveridge about those matters. It must be about ten years or so ago he wrote a book.
A Defense of Learning, I think it's called.
I don't remember what it was. I was looking for it the other day, and I can't find it.
I mentioned that I made a study of his paper — the files of that committee, the Academic Assistance Council — they are in Oxford now. They give some of the statistics and background. Well, on another question … We started off on this track by talking about theoretical physicists. Let me extend that to theory in general. Here are specific developments — for example, Yukawa's paper where he postulated the existence of a meson or a mesotron, as it was first called, to explain nuclear forces. You showed me before the copy of that paper that he had sent to you shortly after its publication. I'd like to know what the relation was between experimentalists and this kind of theoretical work. Did it influence your work? I'm talking now of the period from 1935.
No, not really. I have rather a sad and stupid story about that. I don't remember the date. There was a discussion meeting in the rooms of the Royal Society on the cosmic radiation. Rutherford was in the chair, but whether it was in the period when he was president or not, I can't remember, and I haven't come across the paper which gives an account of that meeting. But I had told Rutherford that I had something to say. I don't think I had told him what it was. I'm pretty sure I couldn't have told him or he would have put me right. I had been thinking many years about the cosmic radiation; in fact, to begin with in 1914 when I was with Geiger, because then the subject was just beginning. It was at a very young state indeed, and Kolhorster, who made measurements in the balloon, was Geiger's assistant for time. But I never did any work on it. But I remember discussing the matter with Bothe and one or two other people at this conference I mentioned in Cambridge. It must have been some few years after that when we knew a good deal more about the behavior of the cosmic radiation, that I thought (in fact, I was convinced) that you couldn't explain all the properties of cosmic radiation on the basis of the behavior of gamma rays of whatever energy and electrons; and there must be some particle with the same charge as the electron but with a much bigger mass — of the order of a hundred times the mass of the electron. That was what I was going to say at this meeting. Rutherford called on me.
By that time I had got very nervous about it indeed, and I just did not have the courage to say what I had intended to say, and I invented quite suddenly some remarks of a trivial nature. If I remember rightly, it was about some suggestion that Millikan had made — I can't remember exactly what it was. But I remember that after the meeting I had been invited to dine with the Royal Society Dining Club, and I happened to sit next to Eddington, and I told him about it with the addition, pulling his leg in a mild way, by suggesting that the mass of this particle would be equal to the square root of the mass of the proton multiplied by the mass of the electron. He was then at that time busy starting this general explanation of his of the whole of the universe. I don't know whether you remember it. But he ended up with about 37 or 137 equations which explained everything, and there was nothing you could suggest to him that he couldn't explain in some way or another even if he had to invent a few more equations. But I dropped it, and it may have been due to the stimulation of Yukawa's papers, or it may have been that some other work was going on somewhere else that induced me to get E. J. Williams (it may have been that his mind was already on those matters) to make experiments in Liverpool. He observed some tracks which appeared to be electron tracks but which were more heavily ionized than the track of an electron. I wrote to Rutherford about it. There were quite nice photographs. I don't think that the work was ever published. I don't know why.
Had Anderson published by that time? I'm referring to Anderson and Neddermeyer on the mesotron. I'm not talking about the positron. This would be about 1937.
Well, these experiments were, I should say, in the winter of 1936, '37. You see, that letter of Rutherford's was dated October 1937, and it was some time before that, I'm quite sure, that I had written to him but I don't really remember very much about this except that so far as I was concerned, these were the first photographs...
Just as we ran out of tape on the other side, you were saying that you believe this was the first photograph of the meson.
That may not be true, but it was the first photograph that convinced me. But there were various difficulties at that time, difficulties connected with the building of the cyclotron, which were exasperating. We couldn't get on with things. You couldn't get the things made and delivered at the time that was promised because most of the outside work was done by Metropolitan Vickers, and they were busy indeed with the defense contracts. I didn't realize it at the time, but I knew that they were extremely busy. I had to pay several visits there. I had friends there who tried to help me, but they were unable to do very much, and one of them suggested that I should go myself and talk to the head of the workshops, who was in charge of the workshops and very much in charge. I could see my bits of apparatus lying about the place waiting for their turn but their turn never coming, because they were big. I think there was only about one lathe in the place which would take them. At the same time, you see, I was building up my own workshop in the laboratory, buying new lathes and reorganizing the place as well as reorganizing the teaching. So I was reasonably busy, and in some ways rather worried that it seemed to take so long to get anything done. It was coming along, but it was very slow work.
Was it more difficult to get things done in Liverpool than it would have been in Cambridge?
Well, yes, because our workshop was not very good. We did not have the technicians that I needed and a very small staff. There were not the people about to give me advice about some of the matters. But at that time, you see, I had Kinsey; and I forget when Walke came along, but also he knew something about it. I could also ask some of our engineers, but these matters were rather outside their interests, and we had to rely upon ourselves. We had to build the valves, for example, that operated the machine, because I couldn't afford to buy them. Well, there were one or two available which might have done the job, but in any case, I had to be very careful of the money, and I had to buy a rectifier of considerable capacity. In fact, I had to buy that from Germany, but at that time the Germans were very anxious to get hold of money from abroad, and I got it at a very reasonable price. But it was the only one in the country of that type, and after the war began, some engineers came from English Electric to have a look at it and study its design because it was the only one in the country. I'm rather off the subject.
That's good. It fills in background. Let's return to the subject of nuclear forces and this talk that you didn't give at the Royal Society on the subject of the possible existence of a heavier particle. Can we try to date that? You said you couldn't remember the date. Now, it certainly was before Yukawa's paper. Was it between the neutron and Yukawa's paper in those intervening years?
I don't know. I just don't remember, and I haven't seen any reference to it anywhere. But I must add this, that I wasn't then thinking that such a particle could have any part to play in the nuclear forces. I wasn't thinking about that at all. It was just simply that I was sure that the phenomena shown by the cosmic radiation could not be explained on the basis of gamma rays and electrons and that one had to bring in a particle with the same charge as the electron but with about roughly a hundred times the mass. That was all. It didn't go any further than that. I shouldn't have mentioned that, but it does connect up with that remark in Rutherford's letter, and perhaps it connects up — yes, I think it does — with a little note that was written at the time I was awarded the Copley Medal by the Royal Society. I can't tell you the date. I can find out. But it was at a time when I was not at all well — in fact, I was in bed most of the time for two or three months. My health had given way because I'd had no rest since being in the United States, which had been a very heavy time for me, and my reserves of energy had given out. But on coming back — when you're awarded a medal, some little screed is written about it, justifying it.
There is a special term for that.
Yes, there is.
It has to do with the presentation.
Well, I don't know who wrote it, but there was a remark in it. I can't remember the words.
A citation. Yes, that's the right word. Which suggested that I was rather lacking in imagination but otherwise a very good experimenter. Well, now, I must say that irritated me slightly. It amused me at the same time, because I knew that I wasn't lacking in imagination. What I did fall down on was in telling people about the things I was thinking I very seldom indeed told even Rutherford to whom I would naturally speak. But my difficulty was not so much that I had a lack of imagination but that I could generally find two or three different explanations of the same phenomenon, I was always most, unwilling to speak about them until I had done the experiments, until I had evidence on the way things were going. And, of course, that depended upon being able to do the experiments, and I was restricted, not only by facilities but by time. There's a limit to what one can do. But I had thought about a great many things.
In this connection on the nuclear forces, you said that that particular cosmic ray explanation had nothing to do with nuclear forces. You were leading into something, I think, that related to that; that it did have relations to something else. You didn't pursue that. I don't know what you had in mind.
Well, if this particle existed, how did it get formed? I suppose that if I had been able to find it or somebody had been able to find it, I should have thought about its function of if it had any function in the nuclear structure, because there was always the difficulty of understanding why a neutron and a proton didn't combine. Obviously, something would keep them apart at short distances. And in the first paper I wrote, the Royal Society paper, I remember putting in a diagram. Stupidly I didn't explain what it was about. I did put in a repulsive force, but I didn't explain that this was meant to be at very short distances. It was worrying me then. Also, why didn't two neutrons combine? Why wasn't there a neutron with two masses instead of one? I looked for it as well as I could, but of course there was no evidence for it. And, as far as I know, there isn't one. But although the discovery of the neutron did help in a great many ways, there were still a lot of quite fundamental things which were most unclear. They were in my mind, but I don't suppose I said very much about them. Everybody must have had much the same ideas. These ideas are fairly common. People think in much the same way.
You discussed some of these questions in 1937 in your Kelvin lecture, and the title at that time was "The Elementary Particles of Matter." And in it you said that the main problem in nuclear physics is the nature of the elementary particle and the nature of the interaction between these particles. By the time you gave this talk in '37 you were building the cyclotron. Did you see then that you were further along on the path to solving some of these fundamental things ...?
Well, that was the idea of building the cyclotron. I had no particular interest in observing all these disintegrations. That was easy, inevitable. One could do that. It amused some people; it didn't amuse me. It was unlikely, it seemed to me, that one could get any clue to the nuclear forces from experiments of that kind. It was in the nuclear forces that I was particularly interested, and my idea in building the cyclotron was to study the forces particularly between the neutron and the proton. And possibly in some way, by producing neutrons by proton bombardment, use these neutrons to study the forces between the neutrons and nuclei. Again, I say I was not interested in these artificial disintegrations. I had had enough of that, and there was very little more than descriptive botany.
Was this feeling widely shared?
I don't know. Well, there were always a number of people who would be interested in the disintegrations, particularly, for example, Walke. But that wasn't going to interest me.
The cyclotron, of course, could have been used for several purposes.
Yes. I have no doubt that we might have done a few experiments of that kind to keep some of the people quiet really, to satisfy them that something was happening. I realized that it was not going to be easy to find out anything about the nuclear forces. It never had been. It was going to be a bit easier by having protons at high energies, which wasn't so very high compared with what Ernest Lawrence had, but at any rate it was a great deal more than had been available in this country.
Was there any other intended use of the cyclotron? For example, in California they were using it for therapeutic purposes, for radiation therapy — and this provided a source of funds for them. Was there anything similar going on here?
No. It was in my mind, but my cyclotron was not powerful enough for such experiments, and I should have been unwilling to spend much time on them. But I had mentioned such experiments many years previously — I don't know when it was. I was invited to give some lecture to a medical society in London called, if I remember rightly, the MacKenzie Davidson Lecture. I haven't come across a copy of it; I don't know what I've done with them; but I'm quite certain that I mentioned the possible application of neutron bombardment to cancer. And certainly a little later, if not then, I had in mind the production of artificial radioactive elements which could be used not merely as tracers to investigate some of the bodily functions or behavior, but also it might be possible to find some elements which would be more readily absorbed in cancerous growth than in the normal cells. But I don't think that I mentioned these things in my Mackenzie Davidson lecture. I think that was too soon. It was certainly in my mind much later on. The cyclotron wasn't ready before the war, so I must have mentioned these matters after the war had begun. I remember I was asked to give a lecture at the Manchester Literary and Philosophical Society, and my mind was then running as a sideline on the applications of physics to medicine. I couldn't talk about the work we were actually doing, because it was on the nuclear bomb. And so I did talk about these other things. Amongst them I presume I mentioned these applications I spoke about a minute or two ago and also I did try to get people interested in the electron microscope. But I failed.
This paper I see is on my list — I have a partial list — it was in 1942, and it was called "New Applications of Physics to Medicine." It was published in the Memoirs and the Proceedings of the Manchester Literary and Philosophical Society.
Yes, somewhere I must have one.
Then you have another article on "The Cyclotron Applications." There was a copy of that in Nature in October 1938.
That would be the summary of a Royal Institution lecture. It would only be a summary. My papers are all in a muddle. I haven't been able to sort them out yet, and whether I ever shall or not …
Oh, I see that you mention the biological aspects in this 1938 article.
Yes. So that's included: "Radioactive Indicators."
Yes, this is the Manchester paper. I'd forgotten all about it really. I tried to interest some of the medical people in Liverpool but without much success. Yes, that's it. But that was quite a sideline.
At the Cavendish in that period there apparently was some work in radium beam therapy going on with a DSIR grant for it. I've come across this in the Rutherford letters. Do you know anything of that? This was after you left. It was in ‘36 or ‘37. Let's see: Who was associated with it at the time? I don't seem to be able to locate that.
Do you think it was in the Cavendish?
Well, Rutherford mentioned it in a letter. He's talking in terms of a specific man. I don't seem to be able to locate it here. Here: in ‘35. All my note says is that there was a letter regarding radium beam therapy and that it had to do with a grant from DSIR to someone, but I don't have any further details.
That's very odd, because Rutherford had very little interest in that aspect. And there was a man working with me at about that time called Douglas Lea. We did one thing together — that was to search for the neutrino — but he did some other things on his own. He went to medicine, and Rutherford, I remember very well, was rather annoyed; and he was annoyed with me because I'd encouraged Lea to do this. I don't think he lectured at Cambridge. I think he went to the Strangeways laboratory, and he became quite well known. He was an able man, and his interest lay that way. Rutherford regarded it as a loss to physics. I regarded it as a gain to medicine. We just disagreed on it. Unfortunately, Lea died at a very early age. He did some quite good work. His name is remembered in radio-therapy circles. I mention that because at that time Rutherford showed no interest whatever in medical applications. We had no facilities in the laboratory for such work. We couldn't help people either. We hadn't enough radium to be of much use. And in any case whatever we had we needed, although we needed it less as time went on, you see, because it wasn't so useful as it had been.
Well, because your interests had changed.
Yes, because we wanted higher and higher energies, and we wanted things which we could control. There was a very big change coming over physics at that time. It wasn't merely that one needed these big tools, complicated pieces of apparatus; their very use made a change in the training of students. In the earlier days we had been able generally to give each man a problem of his own. In some cases two men would work together. That was at first rather unusual. As time went on it became more usual. And with the growth of these accelerators, people had to work in groups; and that in itself made quite a change. And it's gone on in that way. You find half a dozen people working together and all putting their names on the publication. And so it makes it very difficult to ascribe any particular thing to a particular man. Now, that difficulty would arise very acutely in Cambridge, and Oxford, particularly, because the brighter men would be candidates for the college fellowships. Well, then, they would have to produce evidence that they had done something. It wasn't that they'd done it with a group. You'd want to know what the man himself had done. Well, if you have a large group, you can't pick out the contributions of one man. It's a great handicap to young men in some respects to work in groups. I've been saying for many years that you have to manufacture in groups, you can discuss in groups but you can't think in groups, and a scientist — well, anybody — must have quiet and solitude in which he does his thinking. That is why I don't like this working in groups — it is unavoidable — and why I think a laboratory should be closed at night as a general rule. Men must have time to think. I don't like this habit of working — unless there are occasions when one must work almost 24 hours a day for short times when something exciting is happening, but that's quite a different matter. I have seen so much time wasted by men doing experiments, setting up experiments, without really thinking about the matter. They could have saved themselves such an awful lot of time and trouble by some quiet thinking. Of course, everybody has experienced that. Rutherford was always very definite about it — very clear about it.
There's a role here, I guess, for fashion; that when someone is following a fashion he's less apt to do analysis and to think about it, but rather goes along a certain line, because this is expected and is where he thinks pay dirt will be.
Yes. And that, you see, is emphasized when one is working in a group. But, of course, it is inevitable at the present time.
Before we get into some of these group developments, I want to touch on one more thing when we're talking about theory in the 1930's, and that is the compound nucleus and perhaps other models of the nucleus. I came across a letter in the Rutherford papers which described his reaction to a visit from Bohr in 1936, February 1936, where Bohr told Rutherford of his ideas of the compound nucleus.
Hadn't Bohr published anything by that time?
I think Bohr published about that time, but apparently this was the first Rutherford had heard of it. But I don't think Bohr had published the whole thing.
My memory must be wrong then, because I thought I had discussed something of that kind with Niels Bohr before I left the Cavendish, but I'm not sure. My memory may be wrong. But, you see, an idea of that kind must have been in the mind of a number of people, very vaguely perhaps. I'm quite sure that something of the kind had been in my mind for some little time, but I had never pursued it properly, certainly not in the way that Bohr did. And whenever it was that he began to talk privately about these ideas and publish something, it was a very great help and immediately accepted as a beginning towards understanding the structure of the nucleus. It was naturally only a beginning, but it was a very definite help; and I should say quite generally accepted. Somewhere amongst these papers I have some notes on the drop model. I was looking for it just before you came in. I mislaid it somewhere here. It was written certainly during my early days in Liverpool and probably for some lecture or lectures to the few students I had who proceeded to stay in the laboratory after their degree. I had a few, a very few, but the numbers began to grown and would have grown if it hadn't been for the war. But there were some. T. D. Pickavance was one of them, who is now the director of the Rutherford Laboratory. Then J. R. Holt, who has a chair in the physics laboratory in Liverpool, stayed on. He was one of the best students I ever had. There was another who was quite able, Stanley Rolands, but he later went into medicine. And later having a job as a radio physicist in St. Mary's in London, he took a medical degree because he realized that his work and his interests would be restricted if he didn't have a medical degree. So he sat down and took one. He's a man of considerable general ability. I don't say he was a very good physicist, but he could have been if he'd had greater opportunities or perhaps lived a few years earlier. But he joined me at a time when men were being taken into the services, and he had an interview and he was told the Naval people were interested in him because he had done a certain amount of sailing and he was told that they would be ready at any time to give him a commission. But he wanted to stay and work. We were then working on the nuclear bomb business, not that some of them knew much about it, but they knew they were taking part in the work. We kept it very quiet, as quiet as we could. There were people in the laboratory who knew what we were doing, the kind of experiment that we were doing, but had no idea why. By not talking about it very much or rather by talking about it … (slight interruption) I'm jumping years now, but I didn't hide what experiments we were doing from people in the laboratory who were not concerned with them. But I didn't tell them the reason. By not hiding things, they didn't suspect the reason for it. It seemed to me the best method of not creating any undue curiosity.
You didn't call any special attention to them by treating them in any different way.
We treated them as just an ordinary laboratory experiment.
Well, I think we had our cue that we'd better stop for a while. And perhaps next time we can talk about fission itself in terms of physics, how this came about, how you reacted. And that sort of leads into the next period, which I would like you to describe in general terms, in terms of the development of nuclear physics, rather than the war project, which I think has been documented in a more extensive way elsewhere.
Yes, it has, but the whole truth has never been told. In my opinion, when I resigned my post here and retired to the Vale of Cluet, I had intended to write something about those times. Then books began to appear which to me give the wrong impression and in some cases made wrong statements. I began to realize that I also had a limited view of the whole thing, and there might be things that I didn't know that I should have known that were important, and that restrained me from writing anything for publication. I made a few notes and no more. (Pause in recording)
We're resuming now after a break of a few hours, not very many hours. And at the time we stopped I was about to ask how you first heard of nuclear fission.
I don't remember. I suppose really from the letter of Otto Frisch and Lise Meitner written in Nature, because that, I think, was published before the paper of Hahn and Strassman. That one can find out from the dates. You see, they didn't publish until January 1939, I think. I can easily check it perhaps from Hahn's book.
I think it was earlier. I think they already had a paper.
Oh, they had some, but they didn't publish their conclusion that one of their substances was in fact barium and not an isotope of barium or something with similar properties.
I know that Meitner and Frisch discussed this around Christmas, around the Christmas holidays in 1938, and that means that they had published yet.
No, it was a private letter from Otto Hahn to Lise Meitner, who had worked with him for so many years, and he was just telling her that they had come to that conclusion. But then I think the publication was in January.
But in any event your recollection is that you first heard of it by reading the article by Meitner and Frisch in Nature sometime in January.
I think so.
What was your reaction? Do you recall that?
No very great surprise actually. It was a surprise, but it wasn't a very great surprise, because I had expected that uranium would disintegrate under the bombardment of neutrons. As a matter of fact, Goldhaber and I looked for it. I mean we looked at some of the lighter elements and then the heavy ones. In between they would be much more stable, and we looked at uranium, but you see we looked for particles with ranges greater than the alpha particle. Now, that was really quite a stupid thing to do. We were expecting particles with longer range, and we covered the uranium with a metal foil sufficiently thick to be sure of stopping the alpha particles. Now, what we should have done, which would have been much simpler in some ways, was to put a bias on the valves so as to cut down the sensitivity to such a degree that the alpha particles would not be recorded. They'd be in the background, in a kind of zero trace. Now, if we had done that, of course we also limited our powers of observing some particles, but we should have found the fission. It was, I suppose, one of those stupid things one does do. One doesn't think enough about it. We didn't think about fission. That was the point, of course. And there were a lot of very odd things found about the fission of uranium. I suppose Fermi was the first with transuranic elements. Everybody believed it. And the Joliot-Curies did some experiments, got some queer results, and Hahn and Strassman did. But actually some woman, whose name I've forgotten…
Yes, she pointed out in some chemical journal — I think probably Hahn mentions it there; I'm not sure — that perhaps the uranium nucleus had divided. Of course, I never saw that. If I'd seen that, I should have… Well, when I say "I should", I might have grasped the point. I ought to have done so anyhow. So ought other people for that matter.
There are some people who did see it. The Fermi group, for example, knew of the paper, but they didn't do anything about it.
Oh, I don't remember. I'd forgotten that if I ever read it.
But had you been in touch with Ida Noddack? I guess her husband was also involved in similar work.
No, I knew nothing about her.
You knew nothing of their work in general.
Not of hers, if she'd done any at all. I don't know. Had she done any?
Yes, they had been publishing.
I don't remember it. And this note about the possibility of what was later called fission was in some chemical journal, which I wouldn't normally see.
Well, when you heard the news, it seemed obvious then and it seemed clear that that was what was involved. But what did you do?
Nothing. I was busy. I didn't see any interesting consequences from it. Later, yes, but it was a few months later, I saw that there could be interesting consequences, as almost everybody did, but I didn't see anything of special physical interest. It seemed to me that if something could be done with it, it would be a technical development rather than a search for new physical facts. It didn't seem to me that there was anything particularly new to find out. In fact, I had no resources for doing it anyhow, but it struck me at the time that this was very largely going to be a matter of technology. And it mostly was. That was in thinking about the slow reaction. And, of course, it was the Bohr and Weheeler paper which, as far as I was concerned, made a change. But by that time I had had a letter from Edward Appleton, who was the secretary of the Department of Scientific and Industrial Research, and apparently some questions had arisen in his mind or suggestions had been put to him by various people, and he wrote to me about the possibilities — I don't know how he put it, because I can't find the letters; I may have destroyed them when I left Liverpool; I probably did, but it's just possible that they are in a big envelope in Churchill. When I tried to find them I couldn't find them, and I did get copies of my answers to him, which have also been destroyed, from Mrs. Gowing at the time she was writing her book; in the first draft she quoted them or some parts of them. But it was Appleton's letters which made me think about it. The gist of my reply was that as far as I could see, without going more deeply into the question, there was little or no military possibility. I said I would think about it again. He may have written to me again — I don't know. I did write to him again — I don't know about what time; it would probably be lateish November. But by that time I was convinced that the slow reaction had little or no significance as a military weapon. I didn't go into detail in my letter, but the argument was quite clear to me that the slow reaction was due to neutrons of thermal velocities, and the reaction would proceed with thermal velocities; so you got a great development of heat, and the material would expand and stop the reaction. And at the same time you would want very large amounts of material, very large. Now, wasn't it Francis Perrin who had calculated roughly the physical size for a reaction of that kind and published it in the Comptes Rendus? It was a very rough calculation but sufficient for the purpose. I forget the answer that he came to — 50 tons, that kind of thing. I tried to do the calculations a little better, not having the slow reaction in mind, but having the fast reaction in mind. I'll come to that later. But I found that it was too complicated for me, and fortunately Morris Pryce was still available. You see, about half my staff never returned in October 1939. They were already absorbed into the radar business and didn't come back.
When did that happen — when they began to get involved in radar?
During the summer. There were quite a number of men from all over the place who were dragged in, chiefly from Cambridge; and my department, and Birmingham…
Was this done on an individual basis? In other words, particular men were asked?
Yes, as far as I remember. But Pryce was not amongst them, and he was capable of doing almost any calculation that was at all feasible. We didn't publish it, because I realized even then that if there was anything in it, it ought to be kept quiet; and if there was nothing in it, well, it wasn't worth while publishing anything about it. But one of the reasons I asked him to go into it very carefully was because I began to perceive, which I ought to have done much earlier, that the only reaction which could have any military significance would be one propagated by fast neutrons. Well, now, that's where the Bohr and Wheeler paper comes in, because they gave very good reasons for believing that the uranium 238 would need fast neutrons at higher energy than 1 million volts to disintegrate that nucleus. There were only two measurements of the fission cross section for fast neutrons at that time. One of them was by Landenburg and that doesn't come into the picture because it was with neutrons, if I remember rightly, of about 2 million volts energy, so it did not apply to the 235. That measurement, in fact, I don't think was quoted by Bohr and Wheeler, but Bohr and Wheeler did quote a measurement of Tuve's. And he had measured the cross section (it must be in this little notebook somewhere; I copied it out for certain reasons from an old notebook, and it must be in here; I've lost the old notebook) of uranium for neutrons I think of 600,000 volts energy and a little over one (million volts). Bohr and Wheeler, Tuve and his collaborators, reported at the Princeton meeting of the American Physical Society, quoted by Bohr and Wheeler at page 444 of that issue of the Physical Review, which reached me, I think, in October of 1939. And they measured the fission cross section for .6 million volts and for neutrons of 1 million volts. Now, Bohr and Wheeler gave what seemed to me pretty good reasons for believing that the threshold of U238 would be around 3/4 of a million volts. So I couldn't go wrong. I don't mean that I couldn't go wrong. But if I assumed that the whole cross section at .6 million volts was for the fission of U235, I could only be overestimating it. And so I took that. Now, one reason for getting Pryce to do a calculation that was of a critical size properly was to take into account the scattering of the neutrons in the material
. I did not know about how much the inelastic scattering would be, but there would be some, which would reduce the velocity of the neutrons; and I had to make rough assumptions about those matters. But the really important point was this fission cross section from the measurements of Tuve; which came out very low. And so I made an estimate of the critical size, and it came out — I don't remember — but something quite big. It was some tons, if I remember rightly. Getting on for a ton of U235. Well, it certainly would have made a hell of an explosion, but it was not feasible to think that one could separate one ton of U235. So when I wrote to Appleton, I said something to the effect that there didn't seem to be much in either possibility. Now, you see, at that time I was indeed very busy — half the staff gone, extra work to do, and so correspondingly little time to think. But I kept on thinking about it. I was very worried about the possibility — and it practically all depended on these measurements of Tuve's with this fission cross section. And of course, I had great respect for Tuve; he was a very good experimenter. But I began to think: "Well, this is too damn low altogether." I mean the total cross section must have been of the order of the nuclear diameter, and that meant a very small fraction of the collisions resulted in fission — a very small fraction indeed. So when it came to Christmas I had a few days at home, and I thought more and more. Things had been slowly getting a bit clearer in my mind, and I decided that the thing was too important to neglect. I had to measure the fission cross section. It isn't that I disbelieved in Tuve's measurements, but it seemed to me much too low; and in any case I must measure it myself. So I remember most distinctly sitting down the day after Christmas Day and writing to Appleton to say that I had had further thoughts about the matter, that I was going to carry out certain experiments to get things clearer, and that I might need his help in some matters.
I thought I might need some money or I might need some assistance. He wrote back and said that he would be ready to help in any way it was possible and followed it up by sending me a bag of uranium oxide, which I didn't need. I had enough uranium oxide to do the experiments I had in mind. What I had to do then was to change over the arrangements I had on the cyclotron so as to make measurements, to get a beam of neutrons of definite velocity, and make measurements of the fission cross section. Well, that was a somewhat slow process. I was still doing it when I was asked to go to a meeting in London. I haven't got my diary, and I don't know when that was. But I went to a meeting, and I discovered that there had been a committee appointed to consider the general uranium matters. It didn't seem to have done very much, but at that meeting a memorandum written by Frisch and Peierls was produced which pointed out the possibility of a military weapon and made an estimate of the amount of U235 which would be needed based on a guess at the fission cross section. They just guessed the fission cross section to be two times ten to the minus 24 (2xl024), which was miles above Tuve's estimate. I doubt very much whether they had noticed this quotation of Tuve's measurement in Bohr and Wheeler's paper, because they never mentioned it, and they didn't mention it later. However, that's by the way. But I was then asked if I would take charge of the experimental work required to look into this matter. Of course, I said, "Yes." I think I said that I had already started to do something. But I must have said it in a way which was not understood, because I asked Mark Oliphant some months later about it. We happened to be in fairly close contact over certain matters. I told him that of course I'd started on this work the beginning of January before I had heard about this memorandum or knew of this committee which had been set up in London. He was a little surprised. He had been at the meeting, and obviously he had not heard what I thought I had said. Or, if he had heard it, I had said it in such a way that it didn't register.
But then — I suppose it was at about that time or perhaps a little before — I had written to the Royal Society, I suppose through the assistant secretary, to ask if I could use the grant which I was getting from them for cyclotron experiments for some work the nature of which I did not wish to mention. And they agreed, because otherwise I should have been in difficulties. I shouldn't have had enough money to go on, because some things had to be paid for. Some people — one or two at any rate — had to be partially supported, and I had practically no other funds except my laboratory grant, which wasn't sufficient for the purpose. And a little later on — I can't remember exactly when it was, June, I should imagine — Frisch came from Birmingham, where he had been, to work on the fission cross section and other matters connected with it, particularly on the measurements of the fission cross section. He was supported from outside, but I've forgotten how. He was the only one. And for some time he was supported from outside. At some time or other — I can't remember when — the DSIR produced some money to help to pay the stipends of a few people and that kind of thing, but that was later. For quite some time I had to stand all the expenses on my laboratory grants and the grant of the Royal Society.
But if the Committee — I assume it's the Maud Committee…
It wasn't the Maud Committee then. It became the Maud Committee.
Well, Margaret Gowing, I think mentioned that you were asked to become a member of this committee in April of 1940. But if that committee asked you to look into these things, then wouldn't it have been a natural thing for them to provide the funds?
I don't think they had any. There was no suggestion that they provide any funds.
I see. So it wasn't a question of putting pressure on them, saying, "I need funds". You found funds from available sources.
Yes. Well, I mean the Royal Society agreed immediately. I also had Appleton's support if I wanted it, you see. I had said in this letter to him that I might need his help, and he had promised to give it when I called for it. I didn't specify what help, but he would have been quite ready. You see, this Maud Committee was under the Air Ministry or something of the kind. It had something to do with the Air Ministry. But, as far as I know, there were no funds, and certainly never offered any and for some time I had very little contact with them. But then naturally the Maud Committee build up, and we had regular meetings. At that time I had begun to make some measurements, and we found that the fission cross section — while it was appreciably less than what had been guessed at by Frisch and Peierls — it was also considerably more than appeared from Tuve's measurements. I should say three or four times as much. That wasn't the only thing we had to do, of course. We had to look at the inelastic scattering. We had to measure the velocities of the neutrons emitted in the fission to see what there was available, to get some idea of the number. I don't think we ever made that measurement ourselves. I'm not quite sure about that now. I doubt that very much. I think we took that from other sources and also perhaps from — I don't remember. I was going to make a guess really, but I'm a bit mixed up. I wouldn't like to say. But there were a number of factors which were involved, and with the exception of one, everything had been done by April or May 1941. There was one exception, and that was the time of emission of the neutrons — whether there was a delay or not, which would have been quite serious. One knew something about that from some measurements made in the United States on the general fission business, and one knew that most of the fission neutrons were emitted at the time of fission.
But there was a small percentage which were called delayed neutrons — emitted a little time afterwards. But that was the only factor, I think, that we had not measured. I remember the spring of 1941 to this day. I realized then that a nuclear bomb was not only possible — it was inevitable. Sooner or later these ideas could not be peculiar to us. Everybody would think about them before long, and some country would put them into action. And I had nobody to talk to. You see, the chief people in the laboratory were Frisch and Rotblat. However high my opinion of them was, they were not citizens of this country, and the others were quite young boys. And there was nobody to talk to about it, I had many sleepless nights. But I did realize how very very serious it could be. And I had then to start taking sleeping pills. It was the only remedy, I've never stopped since then. It's 28 years, and I don't think I've missed a single night in all those 28 years. I should have said that as time went on other people came into the project. And would it be June 1940? — the French came over. I think it must have been June 1940, because it's mentioned in Mrs. Gowing's book. And John Cockcroft brought Halban and Kowarski to see me in Liverpool, with the idea that we should try to make arrangements for them to go on with their work. Well, I did not have room in my laboratory in Liverpool. Not only that, we were subject to bombing. We had quite a lot of bombing raids there. Practically all the windows in my laboratory were blown out. I don't know exactly when. But fortunately very little damage was caused.
The cyclotron was partly below ground — it was in the basement — because the basement was on solid rock, you see. So although those windows were blown in, the apparatus was reasonably well protected. We suffered very little damage. But they would be blown in. For about a week. They were blown in every night, and we put up cardboard shutters. But during every night they would be blown in again. We'd just put them up in the morning and go on. That was no place to put Halban and Kowarski. I did consider a safe place, Bangor, but it was too far away. So they went to Cambridge, and they were found room not in the Cavendish but in a satisfactory place, and they got down to their experiments very quickly as it happened. But they were concerned only with the slow reaction. And I think it is true to say that Halban was made a member of the Maud Committee. It must have been so. So he got to learn about it then. But it had not been in the minds of the French. That I'm quite clear about. And he and Kowarski and various others who were engaged on the study of the slow reaction…
They were working at Cambridge, and Halban's membership…
Except for Halban, they were not supposed to know about the fast reaction, but I have no doubt they did. It was a little after that, during that summer, that I asked Feather and Bretscher to make some measurements of the fission cross section. I didn't explain to them why I needed them, but they had a high voltage outfit working there, and I thought they would have been able to get a stronger beam of neutrons at relatively low velocity — that is, at about half a million volts or something of that kind — better than I could, and at any rate obtain an independent measurement. But it turned out that they couldn't because the whole apparatus was contaminated with deuterium, and you merely got the fast neutrons from the deuterium reaction. But they were not informed about the bomb business until, I should think, the late summer or the autumn of 1940. And the chief work done up to the time of the Maud report in the Cavendish was some work of Bretscher's on the chemical properties of neptunium. Now, I've omitted two things. One thing is the plutonium business. But all this — I don't mean to talk about all this…
Well, this is covered pretty much in the Margaret Gowing book.
I should think so.
Let me interrupt with a question about the cyclotron at the Cavendish at this stage. How far had it progressed when all of this began to happen?
Well, I suppose it was about at the same stage as mine. But it wasn't used very much, because the Cavendish had been practically denuded for work on radar. There were very few left indeed. Sometime later, which must have been after the Maud report was written, Kinsey, who had been working in radar, went to the Cavendish; and then I asked that our measurements on fission cross sections should be repeated there, and they were; but I can't remember much else that was done there. But they didn't get the same results that we did; but, as it turned out, the result that Frisch and I got was pretty right. I think it was only about one per cent different from the value that is accepted now after all this time. There must have been a bit of luck about that. We were very careful, but I must admit that there must have been quite a little bit of luck. The other thing I wanted to mention was that the experiments of Halban-Kowarski progressed very quickly as far as they could go with the material they had, which was about 200 kilograms of heavy water. But they were able to show … But all this is available.
Yes, considering the limits of our time, and the fact that that's covered in greater depth than I'm familiar with already. In other words, if I had studied that very carefully, then I'd have some specific questions, and it would be different. But what I would like is to just get a general impression from you of the effect of the war and the war work on your own career and on the development of nuclear physics in England, in terms of the effect on specific laboratories. And then what I'd like to do after that is to talk about the post-war plans — whether they were made toward the end of the war or whether they were made just after the war, in terms of what the problems were in physics. By that I mean the kinds of things we were talking about before the fission story.
Well, you see, as far as I was concerned, I practically left physics during the war; that is, after the Maud report, there was really very little more that I could do. We had done all the measurements. We could repeat them. I've forgotten now what we did do — we must have done something. But there were two or three other things with which I was concerned: the making of hexa—fluoride and metallic uranium. From the beginning I wanted some metallic uranium for some reason or another, and Oliphant tried to make some and failed. I tried to buy some from various sources. We did get a little bit, but it wasn't pure metallic uranium by any means. It was largely uranium oxide. And I went to J. P. Baxter, who was the research director of Birman, an ICI section at Widness, and told him about my difficulties. I had to tell him what the matter was about. And, of course, he promised to keep it to himself. And he made the first hexafluoride that I had ever seen and the first large quantities of metallic uranium. And that was done on his research grant from the ICI. Every research manager had a certain sum of money which he could spend at his own discretion. He didn't need to inform the company about it, and he did it without informing the company. It was a very great help to us. Well, that is by the way. That may be said in a book somewhere, but I should think it most unlikely. But back to myself. In 1943, August, I suppose, a group of us went to the United States to discuss cooperation in the project, which by that time was well on its way in the United States — cooperation on the terms laid down by the Quebec Agreement. Well, all these matters are in various books.
Was this your first trip to the United States?
Yes. They had asked that I should go but rather too late. I had offered to go to exchange information, but it didn't happen, and I don't want to talk about that. When I got over there, it so happened that the matter of arranging cooperation fell upon me. I was supposed to go to Los Alamos, and a little house was arranged for me and my wife. But when I got there I found that really there was very little for me to do, although there were very large number of people very busy. Practically all the physical factors that were important had been measured. They were not only known but had been measured. I was wrong, but I felt I was much more needed in Washington to keep in touch with our people there and to see what was happening in different places. Initially, Groves wanted two people. He was not really interested in any others. He wanted Mark Oliphant and me over there. But, of course, that was not cooperation. He gradually found that some of our people were useful, and he would ask me to get other people over to help, such as Baxter, for example, who came over. He had to be released from ICI to do so. And another chemist, Emeleus, the Emeleus who is here now, Harry Emeleus, was with Baxter at Oak Ridge, and then Oliphant; and several other people were with Ernest Lawrence in Berkeley working on the problems connected with the race track. And, of course, we had some people in Los Alamos doing various things — one or two mainly working on the electronic side of the equipment necessary for the bomb and some of the explosive side.
That was how Bill Penney came over. He was not originally connected with the Maud Committee in any way. But, you see, my function was merely to help in any way I could — by supplying people, discussing things with General Groves. It was in a sense political, if you'd like to put it that way. Of course, I had a great deal of trouble over the Montreal group. I've forgotten the time now at which Halban's group was transferred to Montreal in the hopes that things could be started up there. Well, they couldn't. There were difficulties of various kinds, and very little indeed could be done there without considerable help from the United States. And their work had no bearing whatever on the war, and it was quite natural that Groves was rather reluctant to do anything for them. I sometimes say Groves when I mean Bush, Conant and Groves. Bush and Conant were the representatives of the United States on the combined policy committee. They were also the scientific representatives on a United States committee of which Groves was the executive officer. But they were… If there was one, the Army member would have been General Styer. But in fact, practically everything depended on Groves, and it was some considerable time before I managed to get the agreement that Montreal should be helped. I don't know whether this is what you want me to say, but the full story has not been told in a book which I think is called Canada's Nuclear Effort or something of the kind. There was considerable help from the United States. All the metal, you see, came from the United States; all the heavy water had to come from the United States — and a good deal of information anyhow.
Those rules were laid down by Groves and me in collaboration. Groves' interest was to get the job done — at the same time to safeguard the interests of the United States in every possible respect. Well, I had the same interest — to get the job done as quickly as possible, because I wanted it done before the war ended. It seemed to me — and I think Groves would have agreed; I didn't discuss the point with him — that it was important that this should be done before the war ended, because otherwise we should not have known the kind of effect produced, and — well, I won't say have been at a disadvantage, but quite obviously other countries would take up the business. I was quite sure, you see, that the Russians could not be far behind in knowing about the project. Well, of course, they had their methods of getting information, but what I really meant was that the Russian physicists would quite obviously come to the same conclusion; and the only thing that would prevent them from starting on a similar project was that at that time I don't think they had any way of, say, measuring fission cross sections. They hadn't the equipment. But, more important still, I think, was that the war effort was incredibly greater in regard to the facilities available than it was in the United States. I don't mean that the war effort in the United States wasn't great. But, you see, the facilities available in the United States were such that there was always something to spare. And, of course, the project couldn't have been done unless there was something to spare and a good deal to spare. It was a very big job.
But the race for time that you talk of was the race before the end of the war rather than a race against a possible German building and using of a bomb.
Oh, yes. I don't say that we knew that the Germans had done nothing, which is true, but we did know that they couldn't be doing anything on a big scale. I think we were quite sure of that. You couldn't hide the evidence of a development such as Oak Ridge or the other place.
Yes, but particularly a place like Oak Ridge. Any air reconnaissance would have shown it up, and such reconnaissances were made.
Well, without going into the details that are covered in one way or another, this period when you were in Washington, took you to Berkeley occasionally, to Los Alamos and other cities. You acted in a coordinating role, in consultation, advice, diplomacy and so forth, and I assume that this went on until the end of the project, until the thing was completed. The how long after that, after the actual testing … You were present at the testing, were you?
Yes. I wasn't on the actual place. I should have been. But I wasn't. But I saw the test, yes. Oh, yes. Well, some of our people were concerned in it. I was not very happy about it, because I knew that some of the electronic equipment for setting off the charges was not very satisfactory. I did not know how satisfactory the electronic equipment had to be. I thought that these explosive lesses which caused the implosion should be set off exactly at the right time. But I think a certain amount of latitude was possible. Anyhow the thing went off, and there was no method of measuring exactly the size of the explosion. It was just estimated. I wrote a description of the thing to John Anderson, and I think my estimate was about 10,000 tons, but it might have been, say, 5000 to 10,000 tons of TNT. It could have been a bit more. But that was only the beginning. But after that — it was only the beginning — one had to see the thing through. At that time, you see, the material for the 235 bomb wasn't ready. Then there were several questions which had to be decided, not by me but at a much higher level, as to the use of the bomb at all. But practically that was decided by the President of the United States, with Churchill's assent. But then it was a question of which particular targets should be attacked. I think that's all in the books.
Well, were you personally aware of some of the feeling about having a demonstration use of the bomb, the petition and the Franck Memorandum?
Oh, I was aware of them, but it just was not practicable.
Was this the general feeling in Washington?
What do you mean by in Washington?
I mean among the … oh, yourself, I guess. In other words, people knew of this Report and of the suggestion that was considered and rejected.
The Franck report.
Oh, I suppose they did. I don't know. After all, that was a matter for the President of the United States to determine, obviously with Stimson's advice. As far as I was concerned, there was no question about it. It would have been a complete waste of material. To whom were you going to demonstrate it?
I don't know the issue. I know the issues that were raised, but I don't know if the answers were the right ones.
I don't think there was any answer. There wasn't enough material to play around like that. No, I don't have any doubts that the bomb had to be used. And I don't feel any guilt in having taken part in producing it. Why should I? Far worse things happened than that — perhaps not many. But I don't know whether you have ever seen photographs of the destruction produced in Tokyo by firebombs.
I know. I'm not suggesting …
There has been a lot said … In fact, when I was looking through these papers I came across some notes I had made on remarks which had been made on the radio by various people, many of them by John Cockcroft …
We were talking about the remarks by John Cockcroft. I wasn't sure …
Well, I don't know, they may be public, but that's all …
This was many years later.
Yes. There have been so many statements about these matters, and it's so very seldom that they are accurate.
I didn't want to get into that on the same level of these discussions that have taken place; just in terms of chronicling your reaction at the time and also trying to determine what your next step was, how long you stayed on in Washington. It's not clear to me what happened. You stayed on, I think, until 1946.
Yes, there were various things to clear up. There was quite a lot to do, but I really don't remember exactly what happened. I had an office with various people in it. That had to be partially closed down. We didn't need so many people anymore. I was concerned in some matters, not many, which were rather ancillary to the making of the bomb. There were certain supplies of materials from this country which I arranged for. I wouldn't say they were very important, but they were important at the time. Any saving of time was important then. In the United States there was no bomb carrier big enough — I don't mean the plane but the under part — to take this bomb. And so we shipped over one or two Lancaster bomb carriers, and they were tested out. I think for one the machinery did not function properly on the l700th time of use, and that was not satisfactory to Groves. It was good enough for any ordinary bomb, of course. Some slight improvements were made. There were a number of things of that kind. It was all relatively small. And I don't know how many things I had to clear up after the war, and then there was all this talk about arrangements that should be made with other countries. The Committee of the United Nations Security Council was set up to deal with these matters, and I was appointed as the scientific adviser to our representative. Those meetings didn't take place till, I suppose, the spring of 1946. It might have been a bit later, because I remember how hot it was in New York at that time without any air conditioning in the rooms. Oh, there were a number of matters in Washington that I had to get cleared up.
But in the meanwhile, were you beginning to plan for the resumption of physics research in England not connected with the war?
Well, we had begun quite early on to consider what would be necessary, what establishments would be necessary to set up in this country if we were to develop the bomb here.
I didn't mean so much that; I mean in terms of physics research; in terms of the things you were doing before the war.
Oh, I did not have much time for that, no. You see, I had a certain amount to do with the Canadian effort still. It was quite clear that we would have to build some new equipment in the universities to carry on. I couldn't be content any longer with the little cyclotron that I had. You see, people were beginning to think in their spare time about accelerators with really high energies. Oliphant produced a scheme. McMillan had produced his. Alvarez was thinking about the linear accelerator. All that kind of thing was going on in the intervals. And then again I should say one began to think about improvements in the bomb perhaps even before the bomb was being used. That is to say, what is now the H bomb. And there were discussions about that. I think everybody had been thinking about it. It was quite natural. And there were some discussions in Los Alamos. I wasn't there at the time. I got reports about them. Something was going on all the time. Then there was the May Johnson bill followed by the McMahon bill. And there was the question of supplies of material for this country — that is, supplies of uranium. You see, those had been arranged by a sub-committee of the combined policy committee — I've forgotten its names. I think I may say that I was instrumental in setting it up or having it set up quite early on. Now, all the material that had been available I naturally got into the United States project except for the metal that had been left in Montreal by Groves. We were obviously going to need quite largish quantities. There were discussions about this. It needed some little arrangements. We came to an amicable agreement in the end. There were several things which had to be tied up.
When did you return?
I suppose it would be about June l946 I'd been to the meetings of this committee of the Security Council. Our representative on the Security Council was Alexander Cadogan. He had been the Permanent Secretary of the Foreign Office. He had been in all the high level discussions during the war — I mean discussions of foreign policy and that kind of thing. By that time our ambassador — during the time I was active in Washington — was Lord Halifax, but he had returned to this country and was replaced by Clark Kerr, who had been ambassador to Moscow. I went up to the Embassy to meet Cadogan with Clark Kerr and I remember very well Cadogan saying to me: "Well, if this is discussion about the future arrangements on nuclear bombs and such matters, it's really a matter for the physicists." I disagreed completely. I said it was entirely a political matter. The physicists wouldn't have any difficulty in coming to some kinds of reasonable agreement amongst themselves, but it wouldn't mean anything whatever — it was purely political. And I did not think that the Russians would agree to anything. Clark Kerr had no delusions on the subject. He'd been in Moscow a few years, and he'd had a good deal to do with the Russians. It was clear that opinion in the Senate was pretty hard. I didn't see really what use I was going to be on this matter of scientific advice, but there I was ready to help. I stayed as long as I could. I think the business was postponed. I came home.
In the meantime, you see, Viscount Portal of Hungerford, who had been chief of the Air Staff during the war, had been put in charge of the nuclear developments, in the applications in this country, both the weapons and any possible reactors. He was in charge. He was not an engineer — he was an airman. I had met him before. But he came over to the United States. I wanted him to see what the thing really meant. You see, one of the difficulties that I had had in those years was to convince certain people in this country — of whom John Anderson was one — of the magnitude of the project. It was very difficult. And, in fact, it was difficult if you didn't see for yourself. Now, I had seen all sections except Hanford. I wasn't allowed to go. But Portal came over, and Groves agreed that Portal could go to every part of the project and agreed he could go to Hanford. And so I said, "Well, what about my coming to Hanford?" And Groves said, "Yes, you can come if you wish, but if you do Portal will not see very much." There were certain parts of Hanford he didn't want me to see. So I didn't go. I thought it was important that Portal should really see what the project meant. It wouldn't have done any harm to the American project if I had seen the whole of Hanford. I was quite capable of keeping it to myself, but of course, I might have felt it to be my duty to say certain things to my own people in this country. But I shouldn't have understood in a brief visit the importance of one part to the other. I'm not technically minded. I think Groves was wrong in that. But he was right in this way: As I said before, there were two preoccupations — one to get the project finished as quickly and as well as possible; secondly, to safeguard the interests of the United States as far as he possibly could, to restrict information as far as he would and any information I could get. In fact, he told me quite a lot. He treated me very well, because he recognized that I had exactly the same preoccupations. One was to get the project finished as quickly as possible; also, to safeguard the interests of my country. He fully recognized that. And he told me quite a number of things which I was allowed to tell John Anderson but to nobody else. And then it was John Anderson's responsibility what he did with that information. And Groves didn't inquire and it never came up. But those matters were very quickly clear between Groves and myself — within almost a few days of meeting each other. It was a very important meeting and rather difficult, particularly for me, unused to these diplomatic matters. But it all worked very well.
It was a question of mutual respect.
Yes. We agreed very well. I never quarreled with him. He was very helpful in some ways, and I think I helped him in some ways, too, particularly by getting people from this country who could contribute, even if it was only a little, to some part of the project. G. I. Taylor came over a few times. He didn't stay very long. He was quite helpful. Penney was helpful. We had two people who observed the dropping of the bomb on Nagasaki. Penney was one and Group Captain Cheshire, the other, was an airman. I think he happened to be in Washington at the time, but Groves said he would like to have an air officer, and I asked for one and got him. I don't know what it was called: the Operation Crossroads, was it? The exercise in the Pacific after the war when the observations were made of the effect of the bomb on ships. I think it was Operations Crossroads. Well, at least one of our people was in that. That was Titterton, again on the electronics side, and Penney was in it for the measurement of the intensity of the explosion. He had been to Hiroshima. I'm not sure that he went to Nagasaki. But it was quite a long time after the event that he produced the best measurements of the magnitude of the explosion that anybody produced, because he used his brain, and some of the best instruments for measuring the intensity of the explosion were petrol cans.
To see how collapsed they were you mean?
Yes. Very simple indeed, but really quite accurate enough for the job.
There was a group who went over within a few days, I guess. Serber was one, and I don't know who went with him.
Yes, and a little later there was a British group which went over. I have the report somewhere. It isn't worth very much, in my opinion. But when Penney went over he produced a report with masses of photographs of these various cans which happened to be lying about, the inclination of trees, posts and so forth and so on — just quite general, but all coming to the same conclusion. It was only about 5000 tons of TNT. It's generally said to be 20,000. But if I remember rightly, Penney came to the conclusion that that first 235 bomb was only about 500 tons of TNT.
Let me get you back to Liverpool now. When you did return, you went right back to the University to your old post. And what did you find, and what did you do in terms of reviving work in the physics department?
Well, one of the first things I had to do was much more general. I said before on some occasion, appropriate or inappropriate, the Treasury had made a large grant of money for the encouragement of nuclear physics in this country. I don't remember how big the sum of money was, but it was quite considerable. I was appointed chairman of this committee, which was a sub-committee of a committee which had been in existence for some time — I've forgotten what its name was, the advisory committee on something or other, whose chairman was Sir John Anderson. After my return to this country, I was made vice-chairman or deputy chairman. It had been or could have been an important committee, but it had done something before I returned. It had done one thing which I disagreed with very violently, and that was putting all the government work — the business of beginning Harwell, with which I was connected at a distance, (being in Washington at the time) and decisions to do various other things — all those things had been put under the Ministry of Supply, instead of having a separate body. That decision had been taken, and there was nothing to be done about it. The other difficulty was that John Anderson had been a member of Churchill's government, which was no longer in power, and it was a little difficult not only for him but for the Prime Minister to have John Anderson and a committee of that kind, which had been appointed under quite different circumstances. So that gradually faded out. The Nuclear Physics Committee survived for some time.
Well, one of the first things we had to do was to ask the universities if they had any intention of developing nuclear physics in their physics laboratories and then of finding out what they wanted to do. In a sense we had to decide what kind of apparatus could be encouraged in one place or the other. I think it was already decided in my case, because we had the big synchrocyclotron. There was a little mix—up. But that is by the way. A certain section was allocated to the Cavendish, another to Glasgow where Philip Dee was, and all the photographic work was in Bristol. Whatever else there was, I don't know. That went on for some time. And again some difficulties arose. It was really dissolved, and a new committee was formed under the DSI. By that time I had come to the conclusion that I had had enough, that it was time for younger men to take their part. I was getting on to 60.
You would only have been about 57 at that time.
Yes. Well, I'd been away from my laboratory for so long; I had so much to do with committees; I didn't want any more committee work than I could possibly avoid. And I did want the young people to have some say about these things. That was very important. I always remember a remark of Rayleigh's. He said something to this effect: that by the time a scientist has reached the age of 60, his opinions on science were not worth very much. He should keep them to himself and let the younger men have a say. But he agreed that when he did reach the age of 60, he didn't hold that opinion quite so strongly as he had held it a little earlier. But I think there's a lot to be said for that. That's what keeps the laboratory alive — the young men coming in often with quite harebrained ideas, but nevertheless full of enthusiasm, full of desire to do something, and sometimes good ideas.
Was this generation really there? You spoke of the nuclear physics laboratories just before the war, at the Cavendish and then things beginning to blossom at Liverpool and then at one or two other places.
To some degree in Birmingham.
This doesn't appear to be a whole generation of people in nuclear and particle physics. What did you find, for example, on this post-war committee when you surveyed what departments wanted to do in nuclear physics? Did you find, in fact, that many of them had plans in this direction?
Perhaps no plans, but they had wishes. They had no plans because it was a very expensive business at that time to build these big machines. Universities didn't have the money for it.
You mentioned that through the sub-committee funds were made available. Did the institutions apply for grants specifically? Or did you suggest and allocate some money to back up your suggestions?
Oh, it went like this: that with the agreement of the university and the physics department, certain work would be developed there. Then they would make the estimates as to what it would cost — generally, of course, an under-estimate. But I don't remember any real difficulty in finding the money. The money came.
What about the people? Where did they come from?
Oh, they were about. Some of them were beginners. But, you see, during the war both in Liverpool and in Cambridge a number of young people had been working on this project, and some work had continued. It was not very significant, of course, but some had continued in both places. Some of the young men had gone over to the United States and were coming back. Not all came back. Well, all came back, but some went back again — but not many. Then there were quite a number who had been to Canada. And some had been coming up. They may have been trained in different aspects of physics but were interested in nuclear physics, and things went quite well. There was no particular difficulty about that.
Would you say that the people in radar had learned something directly applicable to the new kinds of machines that were being developed — in radio frequency techniques?
Oh, yes, I think that is quite true.
When do you feel — was it about this time — that there began to develop a division between nuclear physics, as it had been dine in terms of studies of nuclear structure and the more specialized separately defined field that we now call particle physics or high-energy physics?
Oh, surely that came later. There were perhaps the first stirrings in the few years after the war, but that came later.
The early ‘50's?
I think later than that. In the early ‘50's, yes, there were just the faint stirrings only, and that of course was from observations of the cosmic radiations, when new particles began to appear. But they didn't appear in the physics laboratories for some time. I was rather disappointed on one occasion. You see, we had developed these special photographic plates for the observation of tracks of the particles. I had returned to the United States — I suppose in January 1947. I was again asked to go as scientific adviser to Cadogan on these bomb matters. I took over with me some packets of these special photographic plates, and I sent them to Ernest Lawrence, who was then just getting this machine going, and I told him what they were. I asked him to use them for any purpose he thought was useful, but to send them back to me to be developed, because the development was rather tricky, and we did know how to do it. Then I would send them back to him. I was not trying to encroach on his ground. I was merely trying to be useful. Well, he exposed the damned things; they also developed them. I don't know whether he sent them all back to me or what, but they were useless, quite useless. There must have been something quite interesting on them or would have been if they had been properly developed, or they might have been if they had been properly developed. But they were ruined. I don't know why he did it. There was no use arguing about it.
It could have been that someone else was involved.
Yes, anything might have happened in those days.
I would like to ask a question which goes back a little earlier about the effect on the Cavendish of a couple of things. One is the breakup essentially of the group that had existed there, with people leaving, Oliphant leaving, with you leaving.
Oh, Oliphant didn't leave until …
Until after you left.
Oh, yes. Only just before the war.
Well, the other part of it really was the effect of Rutherford's death on the laboratory and on its orientation.
Well, Rutherford was succeeded by Lawrence Bragg, who had no interest in the nuclear physics side. It went on, insofar as people were available to the high-voltage sections. The cyclotron was not ready, but all that went on. But he was interested in quite different things, quite naturally. Then came the war, you see, which stopped everything; and some of the people who had been active in the nuclear physics side left. Philip Dee had gone already, I think — had already been appointed to Glasgow. Oh, various things happened. The cyclotron was improved at great expense. There were few people left from the old days. There was one very good man called Devons, who is now in the United States somewhere.
At Columbia University.
Is he? Well, there were difficulties about the development of nuclear physics in the Cavendish after the war, the lack of space amongst other things. It was not easy. It was a pity, because Devons would have made a very active little department of his own if there had been space available, if facilities could have been made available. All that was prepared for. But he felt a bit frustrated. I forget where he went first. I think he went to London first — I'm not sure. Anyhow things came not to an end altogether, but to be more of less of a sideline. It was very largely a difficulty of space. After I had returned to Cambridge in 1948 we had some discussions about it, on how it could be brought to life again or rather redeveloped, but nothing very much happened. Perhaps if I had not been so busy with my own college and so tired, I might have been able to do something, but I felt that my first duty was to my college. You see, I went back there in 1948 just as things were really beginning to move again in Liverpool and getting things going properly, a new building and so forth, and some quite good people. But then I was asked to go back as master of my college, and I felt that it was my duty to go.
It was with some reluctance that I went. I didn't want to leave physics. I didn't think I was too old to start again. But I had a very strong feeling of my debt to the college, a very strong feeling of my debt to the college; and that was that. I had to try to repay it if I could. As the time I got back to Cambridge, the bursar was seriously ill and out of action, and I took over the bursarship as a temporary measure, but that was a very heavy burden really, because I was very very tired. I'd had a very heavy job in the United States. It was not merely the amount of work, which was considerable, but the responsibility for various aspects, which fell almost wholly on me. And the office of Master was quite new to me. I really didn't know properly what I ought to be doing. There was a good deal to be done, because the college has suffered heavily during the war in various ways. And, of course, the bursarship — you had the business of looking after all the money and the property of the College. That, of course, was completely new to me. I had a little help from an old friend and Fellow of the College, who was only in Cambridge occasionally. He was our representative on the International Court of Justice at The Hauge, and so most of the time there. So it was a very heavy time. I had no time left really to get to physics, nor was I particularly … And I suppose by that time Otto Frisch had been appointed Jacksonian Professor, and I thought it was his business — and Bragg's, of course, but particularly his business.
How would you characterize the period from ‘48 to 1959 when you retired as Master in terms of the types of activities that you engaged in?
Oh, interesting in some respects, rewarding in some respects, because I think, I hope, I did repay some of my debt to the College. But it was disappointing, though that's not quite the right word to use, but I lost contact, real contacts, with physics at that time. I was much too busy. I was saying I had a very heavy time the first year, and I was not in very good health. I had considerable difficulty. And then I had to take some part in University affairs. I was then asked to undertake the office of Vice-Chancellor after a certain time. I was not interested for my own sake in doing that, but I knew that my College would have wished me to do it had they known. I asked to be given a year's grace so as to recover my health. I pointed out that I was really worn out and at that time unfit to undertake extra duties, which that meant. But there was a kind of unwritten rule that a man should not undertake the office of Vice-Chancellor at the age of 60, and I was going to become 60 not before I became Vice-Chancellor but during my term of office. It was only two years. So I had to say either "yes" or "no". I took the risk of saying "yes". It should have been "no", because a year later when I was in the kind of training for the office of Vice Chancellor I began to feel very shaky, and I went back to Liverpool to be examined by the leading physician in my judgment in this country, now Lord Corwin of Birkenhead, in whom I had very great trust. He found nothing organically wrong with me, which was very satisfying, but at the same time I knew something was going to happen. What was the matter with me was that I was completely drained of strength, and I had no reserves whatever.
There were times — I don't know that my wife knew — that I couldn't walk up the staircase. I could do it on my hands and knees. And then I collapsed more or less. I had to retire to bed for something like two or three months. I had to give up; I retired from the Council of the Senate. I had to say that I was very sorry but I had to ask to be relieved of assuming the office of Vice-Chancellor. It was very sad, but it would probably have killed me. At the same time that I was Master and Bursar (I think I had given up the nuclear physics committee — I'm not quite sure; that had come to an end, I think) I was also on the council of the Royal Society, and that met every fortnight on a Thursday, and I had my own college council meetings every fortnight on a Friday. A great deal of responsibility fell on me in both. In a sense the Master is more than the chairman at a meeting. The Master of the College has certain responsibilities, but as bursar I often had to deal with matters for which I was not particularly competent. I think I carried them out all right. In fact, I did rather more than that in the end. But what happened to me was that I was removed from the Council of the Royal Society. I didn't know the rules. Because I had had some important college meetings the day after a meeting of the Royal Society, I would often have a great deal of material to prepare, to get ready — I wouldn't go to the meeting of the Royal Society.
So I didn't attend the proper quota. I didn't know there was such a thing. It was in the rules, but nobody had ever actually told me that I was in danger of doing that, Well, I was rather sad about it. It wasn't a nice thing to have done. I mean it wasn't a nice thing for me not to have attended the proper number. But if I had known, I should certainly have put my college first. You see, I had this feeling all along that I owed a great deal, much more than I can tell you, to my college. Well, I think I have repaid it. I put the College on a better financial footing than it had been. That may amuse you. It's rather funny. I wish I'd done the same thing for myself. But a college is a charitable trust, and as such can only invest its money in a very limited way. You can own property and farms and so forth, but you couldn't invest money in equities. It had to be gilt-edged stock. Well, that's a very quick way of losing money. And it was quite clear to me when I looked into things that one had to acquire powers to use your money in almost any way you thought fit, but certainly to invest in equities. It took me a whole year to convince everybody that that was the proper thing to do. As far as I know, no college did have such powers, although one, Kings, had done this on Keyne's advice some years before. But they did it under some special dispensation; I don't know what it was. But then, you see, I got the statutes changed, which meant it could be done with the consent of two-thirds majority of the college. I had to go to the University and then to the Privy Council, so it took about six months more before it was active. But that made a very big difference. I suppose our income now — well, before I left it was at least twice what it was when I went.
That's pretty good for amateur investment counseling.
Well, yes, we didn't do as well as we might have done. I wasn't quick enough to see the point properly, but we did quite a bit; and it meant that we could make certain improvements in the College, have more fellows, which I regarded as one of our duties to the University, and later to build an extension to the College.
I just walked through it.
At West Road. Yes, that was only started when I left, I resigned; I didn't retire. That was a sad business, but I didn't like some things that were happening. I don't want to say more than is absolutely necessary. What it amounted to was that there seemed to be a desire to limit the powers and responsibilities of the Master. They were laid down by the statutes, but they could be interfered with in some ways, and I didn't want to make any trouble, and so I resigned, an almost unheard of thing. I mean there had been only one case of a Master resigning his mastership before this. It was very sad, but I gave no explanation — I just resigned and made arrangements to leave Cambridge so that my successor, whoever he was, would feel embarrassed by my being about. That was one reason why I left, why I went to North Wales. The other reason was because I had friends around and particularly in Liverpool. But I still feel it was a rather sad ending. But I was getting on in years. You see, I was not expected to live so long as I have lived. I remember — it was many years ago now — I don't know whether it was in connection with a change of my fellowship; it probably was a bit of both, in connection with my university posts as Assistant Director of Research, although paid initially by the DSIR — there was an insurance scheme. I had a choice of a scheme maturing at 60 or at 65. There was a slight advantage in going to 65. And the insurance people afterwards went round to our bursar and said what amounted to: "Dr. Chadwick has been rather unwise". Obviously that thought I stood a very good chance of not living to 65. Here I am 77 — to my surprise, too, I must say.
You must have had a sense of satisfaction of those years as Master even though you ended them on an unpleasant note.
Oh, in some ways they were quite happy years. In some ways I think I can say the College really came to life again. I think it was a very lively and active place and took its proper part in the University. But the other thing that pleased me very much indeed was getting to know the young undergraduates. That was a great pleasure. I hadn't known the undergraduates in Liverpool very well. There were not the same opportunities. I mean they just came and went, you see. But in College they dined every night, many of them resident in college, and again in some cases I had known their fathers. And I was surprised how good they were. I really was. It was a great surprise to me and a most enormous pleasure. They were really a fine lot of people, and in some ways better than their fathers, but in other ways not quite as good, because there weren't the same opportunities; money was scarcer; their fathers were, I should say, a good deal more adventurous. But so were these boys in the ways which were possible to them. They would go off into the wilds on their vacations and do all kinds of things — and quite interesting things as well in many cases. They were really a very good lot. I got a lot of pleasure from them. That is what I have missed in the last ten years. I miss it very very much.
I want to ask a general question before we're interrupted. We've covered a lot of ground, and there are probably things that you will think of that you will want to include; and if we have time today, I hope you'll remind me. But I'd like to ask you to think back over all of this and try to identify a period in time or a specific event or series of events that you would say gave you more personal satisfaction than any others?
That's very difficult. I think that the one thing that has given me most satisfaction was what I was able to do in the United States. That may sound somewhat egotistic. Actually, of course, I didn't do very much. I had very little part to play any longer in the details of the project. It was really all done. But I doubt very much whether there would have been any cooperation with the United States — that is, any transfer of our people into the Manhattan Project — if it hadn't been for me. Now, that is egotistic, but it was partly due to me and in a certain degree to Mark Oliphant. Our approach to the United States is often so clumsy, in my opinion, and this particular thing. You see, the ink was hardly dry on the Quebec Agreement when we were sent over. Well, I had a message to go over, catch a Boeing or something, a seaplane. Well, I couldn't drop all y commitments in Liverpool like that, leave my university and department on 24 hours' notice, for anybody. And I didn't. I went later. John Anderson was, I think, rather angry with me, but he didn't say so. I was a few days late. But even so it was extremely difficult to get any contact with Bush or Conant. Conant was absent from Washington at the time, and Bush would have nothing to do with us. The leader of our party then was a man called Akers, who was quite good. I won't go into that. But then I was able to get in touch with Conant, and we talked about things together. Things gradually happened. The combined policy committee had its first meeting, and then we had a series of meetings with Groves and Oppie and Bacher and one or two other people — some of our people — and after a little temporary hesitation we got along quite well. And that was because for some reason Groves trusted me. Things went reasonably quite well.
We were talking about this sense of accomplishment and of personal satisfaction.
Yes, if I had to pick one thing out, I think it would have to be that, because of what happened. It did change the trend of events quite considerably. And I found a few friendships which I have enjoyed, particularly with Groves for whom I had a great admiration. There were some things which he did which I think might have been done a bit differently, particularly after the war, but for his management of that project I have a tremendous admiration. It must have been very seldom indeed that he made a wrong decision even of a minor kind. I'll give you one example which happened before I was there. When Hanford was built he was told by the scientist how much material was needed to be on the safe side. He put in a bit more. And if it hadn't been for that, Xenon poisoning would have put the project back quite considerably. But he had used his own judgment. It doesn't sound like so very much, but it was important. I have been at one or two meetings with him when quite a number of details came up but a decision had to be made which was quite important, and he made the decisions. He made them. He summed up the thing very well indeed, and in my experience always formed the right decision. And he was a remarkable worker indeed, but not very good on personal relations perhaps in some instances, but of course some of the people were very difficult to get along with.
I can imagine.
They were, Of course, it was no doubt a bit difficult for him to exercise patience, particularly in a matter of such great concern. That was one thing. But, of course, there were several other things. One thing that pleased me very much was not merely the discovery of the neutron essentially, but the feeling then that the work that had been put in for years was paying off. Something was at last coming from it. We now saw our way out of the woods. That was one thing. Another thing was, I suppose, making the physics department at Liverpool into a really active place, as it was becoming when I left it, and it became even more so afterwards. It was I suppose at that time the best equipped department in Europe in nuclear physics. I still feel a certain amount of satisfaction. I've only got to think at this moment there are four professors of physics in Liverpool as against one in my time, and all four are Fellows of the Royal Society. Well, that isn't to my credit, but some part of it is. At any rate, I was able to start that kind of thing, with a great deal of help from the University and the people in it and people outside it, too — oh, yes, many people outside. I don't know: one has a number of disappointments in one's life, but at the same time there are always some things which one can look back upon with some degree of satisfaction — when one is made to. I must confess that in the quiet hours of the night the things I look back on are the things I am dissatisfied with. I can remember them very plainly — the things I have left undone that I might easily have done. But the other thing is the surprising amount of kindness one gets in the course of one's life. It is quite astonishing. Those things I remember very gratefully. Of course many of these old friends who have showed me kindness are now dead. There's not many of them left. But I have some friends amongst the young men still. There are some among what I call young men. They's mostly about 40-odd.
I still like to think of that as young.
Well, I do — particularly now.
I think you've identified these areas of personal satisfaction in a very clear way. Maybe this is a good point for us to end.
Yes, I expect it is, because it's already been told once.
Today is April 21st and this is the final recorded session.
You asked me a question. I don't remember the exact form in which you put it, but it was something of this kind: On what period of my life did I look back on with the greatest satisfaction? Now, I don't remember your exact words.
That was the intent of the question.
From the point of view of physics, of course, it's the discovery of the neutron, but what I talked about, I think, was my few years in the United States on the Project; because that had a rather wider significance. Participation in the Manhattan Project was of considerable importance for this country in starting up after the war, and also for Canada. That is why I mentioned it. Now, there was another point. What did we contribute? That is, the British participation. What did it contribute towards the success of the Project? To put it in those words. I won't say that I am not competent to speak about that, but I can't look at it in a detached way. Groves was asked at one point, and it may be in his book, whether the British participation had had any particular — or I should say much — significance. And he said, no, perhaps qualifying it by a few words. Although perhaps we had not many contributions to make, there was an aspect of our contribution which was helpful. That's why I showed you the letters from Groves. Now, the other point I had in mind about those years was a personal one almost entirely. That was my friendship with Niels Bohr. Of course, I had known him for years — since 1913 — but only at intervals and never very closely. But in those years in the United States (and the thing started with his arrival in this country) we were, I think, very close friends; and I got an enormous respect and admiration for him. We didn't talk exclusively about the Project.
In fact, I suppose really quite seldom about the Project itself. About its implications for the future, yes; and, as you know, he tried to do something about that. I was brought into it a little, and he told me his thoughts and what he was doing; but I was also brought in it a kind of backstairs way by our ambassador and British minister. He talked about things in general, about the beginnings of his work, and about his views in the quite early days. I think he was perhaps the only man who really appreciated some of the consequences of Rutherford's idea about the nuclear structure of the atom. It took a couple of years before people really saw some of the obvious things. Now, according to Niels, he saw these almost immediately. For example, what became quite obvious was what was known as the displacement law. That was a bit muddled up at the beginning. It should have been obvious. And it was obvious to Niels Bohr. He never published anything about it, because it seemed to him so obvious that everybody must have the same idea. But there were other things he talked about, such as the implications of quantum mechanics in philosophy. That was a matter in which he was very interested. I believe that he wrote a few articles on it. It interested me very much to hear him talk about those things, but I wasn't sufficient a philosopher (in fact, not at all) to be able to assess the importance of his ideas. I thought they were important, but I couldn't assess the importance. But that association with him during those years was indeed one of the happiest periods of my life. Now, I was asked on one occasion about Rutherford.
The question was something like this: Had he a very acute mind? And I remember — my reply may have been written somewhere — and I don't think the reply that I made was original. I don't know. But what I replied was no, in my opinion he hadn't what I should think people would understand by an acute mind. And the words I used were these: that his mind was like the bow of a battleship. There was so much weight behind it, it had no need to be as sharp as a razor. That was a good way of putting it. But I don't claim that it was an original remark. I may have picked it up somewhere. I don't know. Niel's mind was quite different. He had the same faculty that Rutherford had of being able to concentrate his mind on a matter for long periods at a stretch without getting tired or being bored, and he probed very deeply into a great many matters. His opinions on politics generally were very well worth listening to, and he thought almost as deeply about politics and other human matters as he did about physics. That was very different from Rutherford. And he was in what I should call in politics a rather woolly liberal, with the kind of instincts from early training, but he never gave much thought to it, as Niels did. Well, now, that's I think enough on that matter. But when you say: "What is the most satisfying period?" It's quite difficult to answer, and I picked that out because of its wider implications and because of the associations with Niels Bohr. Now, there was another matter I was going to mention. I think I said from time to time that we did some rather silly experiments in the Cavendish. There was one that was not silly, which came to nothing, and it arose in this way. I don't remember the date.
One of the laboratory people had been in Germany, and he had heard that a young man whose name was Elsasser had some kind of idea that electrons behaved like waves. Now, that interested me very much. I discussed it with Rutherford. Whoever it was, reported it to Rutherford and me together. It interested me particularly because a few years before one of the research students had made a very interesting observation which suggested that electrons could be reflected, but he was unable to repeat the experiments properly. But it stuck in my mind. But we didn't know anything about Elsasser, and so I wrote to Geiger to ask him who he was, whether he was a man of some reputation or not and whether he thought there was anything in this story. Now, I think before I got Geiger's reply there had been a publication by Elsasser in perhaps the Die Naturwissenschaften, only a very short paragraph. I don't think there was any particular explanation — I'm not sure. I got a reply from Geiger in the end. He told me that Elsasser was a young man in Gottingen or somewhere, and he had nothing to say about this suggestion, but he had consulted Max von Laue, who said that it seemed to him a bit of nonsense. Well, I wasn't satisfied. I put a man onto the business of scattering electrons from a crystal surface. It meant the building of a large apparatus almost entirely made of glass, and we could not make it in the laboratory. We had no glass blower — that's one point that I wanted to bring out. Everybody had to do his own glass blowing so far as he could, and sometimes I did it. I had learned in the course of my life a little glass blowing, and I would do the ordinary simple things, but I couldn't do big stuff; nor did I have the facilities in any case, but I couldn't have done it. And we had to get this apparatus made in London. Now, unfortunately, there was an accident, and we couldn't repair it, and the experiments died. But the other interesting point, at any rate to me, about that goes back much further — to my days with Geiger.
When I had come to an end of the work I had started on the scattering of beta particles, which was never completed because of the discovery that the main beta emission had a continuous spectrum, I began to work with Geiger on something or other. I can't remember what it was. It obviously didn't come to anything before the war started. But I do remember suggesting to him at that time that perhaps electrons might be scattered from a crystal surface in much the same way as X-rays. He said there was nothing in it; it was rather a silly kind of suggestion to make, as in fact of course, it was. But I've often wondered what would have happened if we'd been able to do it and found a kind of wave nature of the electron long before our minds were ready for it — anybody's minds at that time.
What prompted you to suggest it?
Oh, just one of these silly ideas that comes into one's mind.
There was no other evidence or no other theoretical need for this.
No. No, it was just the kind of thing: well, why shouldn't one try it and see what happens? As I said before, both Rutherford and I, sometimes together, sometimes separately, did quite silly experiments in the hope of getting out of the morass in which we appeared to be buried. The other point about that story was that we did not have a glass blower in the Cavendish until about the 1930's. I can't remember the exact date. But then we were able to employ a glass blower in cooperation with the chemistry department. The salary was divided between the two departments. I had to find a place for him in the Cavendish, which wasn't easy, but it was done; and I had to be responsible for supplying him with the necessary equipment. It was somewhat meager, but in addition I had to be responsible for deciding the priorities amongst the various requests. Well, that wasn't at all easy, but it added to my duties and had to be done. The point of that was that we were always very much hampered by lack of ordinary facilities for carrying out work. It was a difficult time. But, you see, there was very little money available, and it had to be used very carefully.
On this point, I have a question. Did this account for the attitude of Lincoln, who was in cyarge of the lab supplies and who you told me yesterday felt that he had a special mission to guard over each screw?
Oh, yes. That had been his custom for a long time, and it was very difficult for him to break himself away from that custom. And quite often I had to intervene in a sense — that is to say to Lincoln: "Well, this man must have this, that and the other." It was all perfectly amicable; we were very good friends; I had a great respect for Lincoln. But I must say that the young men found him a bit difficult, particularly when they wanted even a good length of cooper wire. It was not immediately forthcoming. Everything had been run on a very tight string. This is really quite private, in a sense quite private. Nobody but qualified people will be allowed to see these things. I think I must mention what Rutherford said to me before I left Cambridge. I think I told you that when I began as a very young boy he had a somewhat poor opinion of me — that was when I was in Manchester just beginning. It changed with the years quite considerably. At some point before I left Cambridge he said to me on more than one occasion that he was not going to keep the Cavendish chair very long; that he'd made arrangements that he should retire at the age of 67 — I think that is right, but I'm trusting to memory. He also said — much to my surprise — that he wanted me to succeed him.
Now, that was a surprise, and I was quite frank with him. I said I was not good enough to succeed him, and at the same time I didn't think there was anybody good enough in this country, and also I said to him that it wouldn't happen. I knew what would happen. When the time came I was not asked to apply for the chair. I doubt very much whether anybody was asked to apply. I knew from a source I won't mention that I was being considered, and I was asked by one man to say what my plans for the Cavendish would be, and I don't remember in detail what I replied, but I remember very well saying that the Cavendish needed expanding considerably; that they must develop two subjects, not merely nuclear physics but molecular physics, which was becoming increasingly important and had a very great future. But that is by the way, and I'm only saying this because something might be said by others which would not quite fit the facts. Now, I was not dismayed when I was not chosen. In fact, I was rather relieved, because I did realize my limitations, and I also realized that to do what I had in mind — that is, to develop molecular physics and nuclear physics at the same time — would take some years off my life. So I was in a sense relieved and pleased, too, that Lawrence Bragg had been chosen, which I knew would happen. I was quite glad that that did happen. At the same time I must confess to a slight feeling of disappointment in spite of saying that I was relieved. The two things can exist together. I don't know if it was about at that time I was offered the Jacksonian chair at the Cavendish. I can't remember the exact date. It must have been after Rutherford's death, I'm pretty sure, but I was rung up by the then Vice-Chancellor of the University one evening, who offered me the post, and I said no, I was not prepared to leave Liverpool.
We had a little conversation. He suggested that he should make me a formal offer in writing so as to give me time to consider the matter properly, but I said there was no point in it; my mind was quite definite. At no account was I going to leave Liverpool at that time. Different things came up after the war, which I refused, because I wanted to get back to physics, and I wanted to proceed with the development of the laboratory in Liverpool, which was still in a somewhat early stage. Well, that was that. I just wanted to make that clear, because some people in the University were rather surprised that I returned to Liverpool and said so to me, but I didn't explain my reasons beyond saying that I wanted to get back to my laboratory and do some work in physics again. I left it at that. If I might just add a sentence or two to that, it wasn't merely my interest in my own laboratory which decided me that way. There was also my interest in the University as a whole. There were various things going on in which I thought I could help. And there was also my friendships with some of the businessmen in the city, which I valued very much indeed. You see, I was not prepared to go into administration. I was not prepared to leave my laboratory, to come, as I might have done, to Cambridge, because, as I said before, I felt that a purely academic life left me unsatisfied. You see, I must say, some of the business people in Liverpool and some of the friends I made there were not merely men of the highest personal integrity, but men of real culture in the proper sense of the word "culture". I don't mean German kultur but what one used to mean by culture. Also, I must repeat the words of Plato, if I remember them properly, "the noblest of all studies is the study of what man is and what life he shall lead". Now, that I think is still true and will, I hope, always be true. But I don't say that I lived up to it. But it was a kind of ideal towards which I strove to some degree.
You had more of an opportunity for that in Liverpool than here, and you also gave another reason for preferring Liverpool, because of the responsibilities in the laboratory. And yet within a few years after the war you did come back to Cambridge.
Yes. As I said before, I was a little reluctant to do it, but I owed a great debt to my college. I came back to my college, not to physics. I wanted to repay, if I could, the debt which I owed. That was the only reason.
You explained that.
I told it before, but that is the explanation. Now I think we have really finished unless — do you have something that you want to ask?
Many things, of course, but then we'll never finish. Oh, there are so many things. You did mention an anecdotal tale about J. J. Thomson and a bucket.
Well, I've told that once or twice before. I think it is true, because I asked J. J. about it and he didn't deny it. It's really to illustrate the enormous difference there is between the facilities that were available in the early days and that are now available readily in any university laboratory. Well, it was a little before my time in Cambridge. I don't know the dates — somewhere between, I should say, 1910 and 1914. J. J. was in his room, his private room — it was quite a small room indeed, very little bigger than this, not as long but a bit wider — and there was a knock on the door. "Come in", said J. J. In came Lincoln, J. J. said, "Well, Lincoln, you can see I'm busy." He had a visitor to whom he was talking. "Unless the matter is very urgent, you must go away and come at a later time." And Lincoln said, "Well, the matter is very urgent, sir." "Well, what is it?" "I want your permission to buy a new bucket." J. J. said, "What's the matter with the old bucket?" "It's got a hole in it, sir." "Well, mend it." "Well, sir," said Lincoln, "you aid that last year, and I did mend it, but now the hole is so big I can't men it anymore." So J. J. said, "Go away and buy a new bucket and don't bother me anymore."
Wonderful. You don't know when this happened, do you?
Well, I say somewhere between 1910 and 1914. I tell it — it is slightly funny — because it illustrates the lack of facilities that one had. Well, now, if you have a question, it's nearly time.
Did you get through your list?
Oh, I don't think these matter. Oh, yes, there is one matter that I might mention. I looked it up last night; the beginnings of my interest in the history of science, the reason why we're here together today. It was the custom that the Cavendish professor should have a professorship at the Royal Institution in London, and he had the duty of giving five or six lectures on some topic selected by himself. These were given on Saturday afternoons, and of course he had to give one Friday evening discourse. But the selection of the topic and the burden of preparing the materials for the lectures was in addition to Rutherford's duties that was noticeable, so he asked me to help him, and he paid me l00 for getting the material together on the literature of the subject and especially for preparing experiments to illustrate the lectures. Now, I found that most interesting, and the one thing I remember very vividly now (I've forgotten the topic; it may have been something about high vacua or something of that kind) I had to go back in the history to the efforts to produce vacua. And I remember now reading the original story of von Guericke and the Magdeburg hemispheres. I suppose it was a copy of his original publication. But in it there was suggestions about the connection between air pressure and the weather. Von Guericke also made an electrical machine, and he had many ideas on astronomy. Well, the way in which these things were put was most interesting to me. Then I realized that, after all, people though just as deeply undoubtedly 300 or so years ago as they do now, and it was that that stimulated my interest in the history of science. But I very seldom ever went to one of those lectures. I had had enough by the time I had prepared all the experiments and produced a lot of notes for Rutherford to use. I don't mean that I prepared his lectures, nothing of the kind, but I was going through the history of these things, you see, and putting down what I thought were the important points. And some of the experiments we prepared were really very good. I remember there was one experiment I could not reproduce — a well known experiment of Hertz in which he tried to observe the deflection of electrons in an electric field. Under whatever conditions of pressure that I had, when I had a beam of electrons which could reach the end of the tube and produce luminosity, the application of an electrostatic field always deflected the beam. I could not reproduce Hertz's experiment. It was generally supposed that he had so much gas left in the tube that the field in the center between the plates was negligible with the space charge effect. I couldn't reproduce it.
You ended on a historical note. I thank you.