Oral History Transcript — Sir James Chadwick
This transcript may not be quoted, reproduced or redistributed in whole or in part by any means except with the written permission of the American Institute of Physics.
This transcript is based on a tape-recorded interview deposited at the Center for History of Physics of the American Institute of Physics. The AIP's interviews have generally been transcribed from tape, edited by the interviewer for clarity, and then further edited by the interviewee. If this interview is important to you, you should consult earlier versions of the transcript or listen to the original tape. For many interviews, the AIP retains substantial files with further information about the interviewee and the interview itself. Please contact us for information about accessing these materials.
Please bear in mind that: 1) This material is a transcript of the spoken word rather than a literary product; 2) An interview must be read with the awareness that different people's memories about an event will often differ, and that memories can change with time for many reasons including subsequent experiences, interactions with others, and one's feelings about an event. Disclaimer: This transcript was scanned from a typescript, introducing occasional spelling errors. The original typescript is available.
See the catalog record for this interview and search for other interviews in our collection
James Chadwick; April 16, 1969
ABSTRACT: Chadwick describes his life and work from his boyhood years to his retirement. He details his discovery of the neutron in 1932 and nuclear physics work at the Cavendish Laboratory from 1919-1936, when he left Cambridge for Liverpool. Among the important events in this narrative are the following: Chadwickís first meeting with Rutherford at the University of Manchester; his graduate work with Hans Geiger (1913-14) in Berlin, where he was interned for four years as an enemy alien; his return, upon release to Manchester, where he teamed up with Rutherford when the latter moved to direct the Cavendish Laboratory in 1919; his functions as Assistant Director of Research at the Cavendish from 1923-36; his role in building a working cyclotron at Liverpool. More briefly, he describes his relation to the US atomic bomb project, his admiration for General Groves; and his final return to Cambridge where, after the war, he served as Master of his College until retirement in 1959.
Weiner:Weíre resuming now after a pause. Today is the 16th, and when we left off yesterday, we were discussing the end of your first year, your scheduled year at Geigerís laboratory. We were just at the point of discussing how it was that you became a civil intern. You told about being released from the ten-day imprisonment and about the very warm and kind attitude of the Germans who had known you such a short period of time but who had been so kind to you. It wasnít clear to me how that temporary imprisonment was over and how it was that you became a long-term intern.
Yes, well, there is very little to say about that time, you see. It was a very sudden decision to intern all Englishman. I think Russians had already been interned or collected together in some way. All that happened to me, and to everybody else, was that early one morning policemen appeared and said that I had to pack up and go with them. We were put into the stables of a race course near Spandau. A few miles out of Berlin there was a place called Ruhleben. It was a trotting race course. And we were just bundled into the stables. There were beds there. In these stables there were 13 or 14 blocks, I canít remember exactly, in which there were cubicles on the ground floor, in which two horses had been put into each cubicle. We were put six men into each cubicle. You just bundled in and it was a toss-up what happened to you. Of course, I knew nobody at all at that time. The upper floor which had been used for storage, for fodder and such things, was also used for living accommodations, and mattresses of a very rough kind were just put on the floor. We made the best of it. As it happened, I got into a cubicle, I suppose I was in the earlier group, I canít say it was very pleasant, but it wasnít too bad. We were not fed very well. There was an allowance of 22 pfennigs per day per head for food. That was the allowance that had been made in peacetime to a German private.
But, of course, he had not lived on that. He had had food from home. You couldnít live on 22 pfennigs a day. In any case, the rationing had been handed over to some man who was making money out of it. And we got very little indeed. It was so little that we couldnít have lived on it. But fortunately, at that time, food was not scarce in Germany, and they opened shops where you could buy some food. You could actually buy butter if you had the money. But it got to such a pitch that we made a demonstration. We decided that everybody would go and collect their food on a Sunday evening when we knew that the officers would be in the camp and would see what was happening. But the food ran out before half of us had received our so-called ration. And there was nothing there. So that man, who had bought the right to deliver the rations was given the sack, and I believe punished, and things were a little better after that. But you couldnít live on what was provided.
Weiner:Did you stay in that same place in those same quarters for the entire period?
Chadwick:Yes, for four years. In the course of time, there was a little bit of redistribution, and the number was reduced to four in a cubicle. That was much easier, but it was still a bit cramped. And, of course, we had a very strict discipline. I forget what time of day it was we had to get up and have a roll call. Each barrack lined up and was counted. That was rather difficult in the winter because it can be quite cold in Germany in the winter, and in the beginning, we werenít very adequately clothed. We had just been picked up, you see, and dumped in the camp. And I can remember the agony when my feet began to thaw out about 11 oíclock in the morning. Then we had to go to bed very early. I think it was lights out at 10 oíclock — it might have been a bit earlier. Then we rigged up various little lights on our own — what we used to call p-lamps, with dry batteries and so on. We managed. As a matter of fact, in some ways it was a very interesting time because there were all kinds of people there — an Earl, various professional people of one kind and another, musicians, painters, a few raceóhorse trainers, a few jockeys, and a great variety of people. The bulk of the men were merchant seamen. I suppose our total was about four thousand in the camp, and at least a thousand were merchant seamen whoíd been caught chiefly in Hamburg.
Weiner:Of all nationalities?
Chadwick:No. There were a few Russians in the camp at the beginning, but not more than about half a dozen, and very soon they were separated out and disappeared. We were all supposed to be English, although some of them couldnít speak English. If theyíd been in this country, they would have been Germans. But by German law, they were considered English. Looking back on it, it was a very interesting time because one met such a great variety of people, I think that was when I really began to grow up.
Weiner:You were only 23 or 24 years old when you went into the camp, is that right? In 1914?
Chadwick:Yes, I was just over 23.
Weiner:How did you become involved in scientific work at the camp? Is camp the appropriate word?
Yes, there were a few men and one in particular, who was very active in all intellectual matters, both arts and sciences, and largely out of his efforts, we formed a society, the name of which Iíve forgotten. One of these barracks was condemned as unfit for human habitation. It was, I suppose, one of the oldest, and of rather different construction than some of the others. It was a kind of wooden structure with the brick in between the wooden beams, and it was so old that a good push would have pushed out the brick. And for that and other reasons which I donít remember, it was, in fact, condemned. So we asked if we could have a part of this for scientific work, or at any rate, to do what we could do which wasnít very much. We had some very ingenious people — one man in particular could turn his hand to almost everything. If he found bits of metal around the camp, he managed somehow to get some tools or to make some, and he built a chemical balance. It wasnít very strong because of the weakness of the beam, but it was quite good, and he built a case for it. How he got the materials, I did not inquire.
One didnít ask about those things. Youíd take any little bit that you happened to see lying about, whether it was part of the structure or not. Nothing very serious, but you took it. We had to do various things of that kind. And we gradually managed to make a few things. We had to make our own benches. There was something there which we could use Ö wood which we could turn into table tops. I came across a man who had been employed by some firm whose name I canít remember, but I shall call it von Bellsbach. It was a firm founded by R. von Welsbach, who made thorium oxide for gas mantles. This man had found that the thorium oxide at one stage of the process was the best tooth paste that he could find. He used it for tooth paste. It was an extremely fine thorium powder — I think it must have been thorium oxide. It was the one thing I started with. I built a little electroscope and found that it was radioactive, much more than I expected. And in one way and another — Iíve forgotten now how we managed it — we got a certain amount of supplies together, probably by persuading a soldier to bring them in, giving him something for his trouble. I built a magnet at one time, that was quite early on. One of the people was a young chemist who had been working somewhere in Germany on liquid crystals. He knew something about the chemistry of the materials which form liquid crystals and it was the first Iíd heard about them. So I began to think, and I thought I might be able to create an order in some liquids by putting them in a magnetic field. And the first thing I had to do was to build a magnet, and then think of the methods I should use, or the instruments I should need to build or acquire somehow in order to see that they had orientated themselves.
I made a sketch of the magnet, the amount of iron and so forth, and gave it to a soldier and he arranged to supply me with it. With another man, I worked out how much copper wire I should want, what dimensions and so forth, something like 300 meters or so, and I got that through this other soldier. And I had to wind the coils by hand. I remember that very well indeed, because it was a hot evening, and the other friends who were working in the same room had all gone to the theatre and left me alone. The temperature was about 36 degrees centigrade. We were in the loft of this barracks at that time, and I got very hot and tired indeed doing all this by hand. But it was done. We had to do a lot of other things. There was a certain amount of what I might describe as cheating going on. We were breaking some of the rules. But the officers must have suspected that but did nothing. They were extremely lenient towards us. Indeed, we did a great number of things that were quite contrary to all the rules. And the officers certainly knew that something was going on. And I remember one occasion on which we were doing something that was very much against the rules, a group of men came in with one of the officers of the camp, and some of them were from the War Office in Berlin. One of the men we didnít know at the time was extremely strict with the German soldiers. He saw what we were up to. He couldnít help but see it. He did nothing.
Weiner:You never made a formal request to use the abandoned barracks? That was allowed?
Chadwick:Yes, certainly we had to make a request, but they agreed.
Weiner:But it was a question of building the different instruments?
Chadwick:We just managed that, and later we got permission to buy chemicals and so forth. Certainly, we bought some things for which we did not have permission, and, in the end, one man got into some trouble. But the difficulty was, you see, that we didnít have any access to literature. I mentioned this matter of the liquid crystals. Before I had really got down to it — I had gotten the magnet built and a few other things — some copies of old reviews turned up, and in one of them I found that what I had been thinking about was quite well known and had been done years ago. So that was washed out, and I started on other things. It was at that time too that C. D. Ellis joined us and was converted to his subsequent career. He was at that time at Woolwich where engineer officers are trained for the Army. There were four or five men of the same standing, though Iím not sure they were all at Woolwich, one might have been at Sandhurst. There were four of them who if they had been at home would have been straight into the Army, and they were in Germany to learn German, just for a few months, and they got caught, as I got caught. And so I started Charles Ellis on physics. When he came back to this country, he wasnít accepted by the Army immediately on the grounds that he wasnít physically fit. Very few of us were. I think only one was immediately accepted out of the four or five, and that was no great blow to Charles Ellis because his interest had turned toward science. But it was a blow to his father who regarded science as something that a gentlemen didnít do, and he was relieved to find that it could be studied in Cambridge. So Charles Ellis came up to Trinity instead of going back to Woolwich or waiting until he was physically fit to be accepted by the Army. There were a lot of very interesting things and I learned a great deal in one way or another about people — what makes them tick. I had always had some interest in literature, but not a very wide one, itís quite true, but I did get much more interested there. Some of my friends were intending to be writers. There were others who were very competent musicians — one or two were musicians by profession.
Weiner:Did they have any opportunity to engage in their interest?
Chadwick:Yes, they were able to get their instruments, and later, a grand piano, and were allowed to have a small room. I donít remember exactly, but they had a room or two rooms in which they could practice, and they had concerts. One of the best-known musicians was a well-known cellist Ė well-known in Manchester at any rate — Karl Fuchs, who was really German by birth, and I believe he had a cottage somewhere in the country near Manchester. That was attacked on the grounds that he was a German, and, of course, he was interned in the camp in Germany because he was English. He didnít stay very long in the camp. He was let out — he was an oldish man. I didnít really get to know him. Of course, there were others, amateur cellists, who were also quite good, and one or two quite good violinists.
Weiner:Among the scientists, or the people associated with the laboratory set-up that you had, how many had previously engaged in scientific work? How large was the total group too? Iím not clear on that.
Chadwick:There were probably about half a dozen who had been engaged in scientific work. As far as I can remember, there were only two who were active in our little laboratory. Iím not sure whether that two is in addition to me or whether it includes me. I should have to think pretty hard about it. One of them was an extremely good chemist, but he was not a university chemist. He was on his own. I suppose you might call him a consultant chemist. He was a free lance. He was a very able man. He had invented a fat hardening process which was quite valuable, but he didnít get anything out of it. I canít go into that now. I mustnít mention that story. He got practically nothing from it although it was used, so he had to set to and invent another and improve upon it. And if I remember rightly, he had been to Russia to see what could be done, if he could sell the process there, and he was on his way back through Germany when he was picked up. Iím not quite sure about that, but anyhow he was very good. And there was another man who had lived in Germany for quite a long time, who had very wide interests, both in science and in literature. He did work with us, but not all the time, because he was allowed to go free and live in Berlin later on. But everything he did turned to an invention. That was what he was. He was an inventor. He made his living by inventing some process or some instrument and selling it.
Weiner:Each one pursued his own interests within this laboratory?
Chadwick:We did what we could within the limits. We were naturally very limited, but things were not as bad as one might expect. We were allowed a certain latitude most surprisingly, and then, an optical manufacturer on a small scale, whose name Iíve forgotten, heard about us and came to see us, and said: ďAnything you want that I have I will lend to you.Ē We did borrow something from him, Iíve forgotten what it was. At that time, Ellis and I were interested in photochemical processes. One of them was the hydrogen-oxygen reaction, and for some reason, we had to drop that, I donít remember why. But the one we were really interested in was COCl2. What is that? Iíve forgotten the names.
Weiner:I donít know the proper terminology for that. (Phosgene)
Chadwick:We found out some things which seemed to be new, and certainly we did borrow from this optical manufacturer some instruments, Iíve forgotten what, and Rubens was anxious to help us if he could. But there was nothing very much that we wanted from him. He sent us one of the instruments, I donít know what you call it, that he had used for measuring heat radiation. I remember the instrument but I forget the word. I donít think we really used it except to see how it worked. Nernst, for example, would have been willing to help us, but we didnít need anything. I was allowed out one day with this chemist-friend of mine to go and see Rubens and Nernst, and they were really most agreeable, particularly Rubens. So while they couldnít help us very much, it wasnít for lack of good will.
Weiner:How about journals? Couldnít they help you with that, or did they have difficulties of their own?
Chadwick:I donít know. We couldnít have afforded them. I did hear about Einsteinís paper on general relativity, I donít know how, and I was able to get a copy of it, so I was probably one of the first English people to know about it, not that I could follow the mathematics. But there was a mathematician in the camp, whose name Iíve forgotten — I think he was a Rhodes scholar in Oxford — he was interested and he gave me a general description of the mathematics. But journals, no. We couldnít have afforded them. I didnít know what was happening but there was no possibility. I ought to mention one thing when Iím talking about this. Taubnitz, the book publishers, offered to send 200 books to the camp and my memory may be not quite accurate about this but the offer was refused. I donít know to whom it came. But first of all it was refused, and then we heard about it. When I say ďweĒ, it was chiefly two or three chemists principally, rather than myself, and we got into touch with them, and we got about 200 books on general scientific things. I expect Iíve got one of them here somewhere.
Weiner:Was the line of research that you pursued pretty consistent? Did you stick with Ellis on the same subject all that time?
Chadwick:That was the chief thing though there were one or two other little things that we looked at. It was a question really of deciding what we could do with the material at our disposal. It was not so much what we were interested as what we could do. In a sense, it was a method of passing the time, but it was much more than that. It kept our interest alive. Itís all rather trivial. It never came to anything.
Weiner:No publications, or anything of that level came out of it?
Chadwick:No, it didnít get as far as that. It interested me particularly in, what should I say, the mechanism of chemical combination, how atoms stuck together, what forces were involved, and so on. And I remember the ideas were not right actually and the calculations were more difficult than I could manage, but it kept me very interested. To some degree, it changed my interest for the time being in chemical matters, because anything else was out of our reach. That really is a somewhat dreary episode but I think it did me, intellectually, a great deal of good because I met so many different people with quite different interests, and I think I began to grow up. Of course, physically, it nearly killed me. I was getting parcels of food pretty regularly from home and a little money occasionally, otherwise I couldnít have helped to buy these things that we got through the help of soldiers by bribing, thatís what it came to. I didnít know how it was done because it was obviously a certain expense upon my parents. When I came back home I found that they had not borne the whole expense at all, but the secretary to the 1851 Exhibition, whose name Iíve forgotten, Evelyn something or other, had made available some money for the purpose of keeping me alive in the camp. It was extremely generous.
Weiner:In a sense, it was an extension of your scholarship.
Chadwick:In a sense, yes, but I donít think they knew that I was really trying to do something. I couldnít say. We were allowed to write letters home but one had to be very careful, and we didnít get very many letters from home. They were censored. We were not allowed more than a very few books from home. For example, I wanted a very elementary book on chemistry, Newtze, Inorganic Chemistry, quite elementary. It was stopped, not by the Germans, but by our English censors, on the grounds that it might be giving information to the enemy. Anything more absurd one couldnít possibly think of. We had difficulties but they are not worth mentioning.
Weiner:The end of this period was 1918. You returned toward the end of 1918. What were the circumstances of your return from the came and your release?
Chadwick:We were just taken out and sent Ö I should have gone with an earlier batch. What happened to them I donít know, but I took the opportunity of leaving the camp for a day or so to see some friends in Berlin without permission. But things were, by that time, in a most disorganized state. You could do almost anything you liked. So I missed the time when I should have been sent home, but it was a good thing because also I wanted to travel home with some of my friends who were in the second batch. We were taken by train to some port on the Baltic — it was a very long and tiresome journey — it took hours to leave the neighborhood of Berlin. I suppose it was Stralsund that we went to, I donít remember. But I do remember that from there we went to the island of Rugen in the Baltic where we had to wait a few days and then we were transported to Copenhagen, and transferred immediately on to another boat which was leaving for Lief. I remember various things that happened on board. We were naturally a somewhat tacky group and we were getting better food than we were accustomed to. One of my most vivid memories is arriving at Lief. I was looking over the edge of Ö what do you call it Ö the tackrail of the boat, when a man who was walking up and down asked me if I knew so and so, who was a friend of mine. It was his son. As a matter of fact, I stayed with them in Edinburgh later on for a day while I arranged to go on the train back to Manchester. I asked him later on why he asked me and not one of the many others who were hanging over the rail. Oh, he said, he thought I looked the university type, but it didnít altogether please me.
Weiner:Even after four years of internment. When you got back to Manchester, I assume that the first period was just one of recuperation.
Yes, you see I could not digest fats, and it was a very trying time indeed. I was quite ill in a kind of way. I was certainly very weak. Iím still troubled by it. My digestion before the first war was exceedingly good. I could digest anything. Itís never been the same since. I still have to be a little careful. But then I went back to Manchester and, of course, I went to see Rutherford, and Rutherford was very short of staff. They were still in the Army and he very kindly suggested that I should do some teaching in the laboratories and earn a little money because I had nothing left. When I got back to England, I had 11 pounds and a few shillings left, and that was all. And one of the first things I saw when I went to the laboratory was Rutherfordís experiments on artificial disintegration. He told me what was happening, showed me, and I sat in on one of the experiments. Of course, it was very exciting. But the chief thing was that it gave me time to recover some health and to earn a little money to keep me going. And then Rutherford was invited to succeed J. J. Thomson as Cavendish Professor and he was very sorry to leave Manchester where he had some friends. I wonít say he was reluctant to go — I donít think he was, in a way — reluctant would be the wrong word. He was sorry to go. But he felt it not only his duty. In those days, the Cavendish professorship was something quite different from any other professorship in physics in this country, or even in any other branch of science, if it came to that. So he had to go. And he asked me to go with him to help him to start up the radioactive work at Cambridge because there had been very little done in Cambridge up to that time. And, in addition, during the war, every effort in the laboratory was devoted to the war effort. There was no ordinary research going on.
Everything had been put on one side. It was quite astonishing to see how little there was in the laboratory. Well, of course, I think I told you before, I had no money. I couldnít have gone without some help, and I was then offered what was called the Wollaston Studentship by Gonville and Caius College. It was only 120 pounds a year, but it was a basis on which I could rely, and I was given to understand that I could earn a little more money by teaching. Naturally, I accepted. The only other alternative was to look for a post in a university somewhere, but I was in a poor state of health, which would have been against me. And I also very much wanted to continue with Rutherford. We were beginning the artificial disintegration and, perhaps I didnít think very much about it, but that was where my interests lay, and I was very glad to accept. As I say, it was made possible by this offer from Gonville and Caius College, which was made more to Rutherford than to me. It wasnít for any concern for me. They knew nothing about me. But it was to help Rutherford.
Weiner:Part of his need.
Chadwick:Yes, he must have explained that he needed somebody to help him to get started, and so it came about.
Weiner:In terms of your educational work, you had completed what degree by this time? You had received a Master of Science from Manchester?
Chadwick:Yes, that was all. There was nothing else. It was about that time the degree of doctor of philosophy was instituted in this country, I should say, partly to keep people in this country rather than to see them go abroad as they had often done to Germany, where they could go get a satisfactory Doctorís degree. The only other thing in this country was the Doctor of Science which would only come after some years of continued research work of some distinction. It still exists. It turned out to be somewhat of a burden to us. No, I ought to continue that story.
Weiner:You mean the artificial disintegration?
No, I was thinking of Ö Rutherford was already more or less established in Cambridge by the time I got here. I couldnít come until the appointed time when the students were admitted. I entered as a reserve student. If I should have needed permission to come earlier, I would then have had to presumably find lodgings. There were certain awkwardnesses about it. And so by the time I got here, Rutherford had dissolved the radium which heíd taken from Manchester. You see it was a personal loan to him by the Austrian Government so he took it with him. I donít know if I helped in the process of recovering it from the solution in Manchester or not, Iíve forgotten. But, by the time I got here, he had redissolved it, and he had fixed up some apparatus for the extracting the emanation, that was up in what we called the radium room, right at the top of the building, so that any escape of the emanation would not permeate through the laboratory. It was admitted to open air straight away. And we had discussed my job before we left Manchester. We had talked together principally about what I should do. He told me what he was going to do. He was going to go on with the artificial disintegration experiments but to look first at the particles he had observed in oxygen, and perhaps other things, which had a range not much more than the alpha particles. Nitrogen was perfectly clear, but the others werenít, and he was going to do that. He didnít say very much about it but he told me that. But the main question, of course, was what I was going to do. And he pointed out that although it seemed fairly certain that the charge on the nucleus was determined by the atomic number, the experimental evidence was more circumstantial than direct, which was perfectly true. It hadnít been measured, and I think I said before, that he was always reluctant to make a definite statement about anything unless he had direct experimental evidence for it.
So he said he thought I ought to measure the charge on the nucleus of certain atoms by accurate measurements of the scattering of alpha particles, and he asked me to think about the matter and how it should be done, how it could be done accurately and I did. When I got to Cambridge I told him I had thought of two ways, one which I didnít think was so satisfactory. It could be done by the way in which I did it. It was rather slow work settling down in the Cavendish. As I have said, there was very little equipment there then. Everything had been diverted to the war effort. There was in fact very little equipment — youíd be surprised. So, gradually, part of my duties in helping Rutherford — it was a matter between ourselves, it wasnít coupled to my studentship at all, there were no conditions of that kind attached to it, but it was understood between us that I was to do anything that I could to help him on the trivial matters. And I began to help in saying, well, we need this piece of apparatus, and ordering them. That came rather slowly. I did help a little bit in the first two or three years with some of the research students, such as Etienne Bieler. I think we did a little work together before he went off on his own.
Weiner:You had a paper published in 1921 with Bieler on ďCollisions of alpha particles with hydrogen nucleiĒ.
Chadwick:Oh yes, of course, stupid of me to forget it, I hadnít really forgotten it, but there were other things so much more important. That, of course, had been started by Rutherford in Manchester, but he was not a very good observer of scintillations. And there were two things I began to do, apart from the actual experiments. One was essential to the experiments. The first thing was to see if we could improve the optical conditions of scintillation counting. That really amounted to looking at catalogues of makers of microscope objectives and finding the one with the biggest aperture. That was what it really amounted to. And, of course, there were better objectives. And, Iím not sure, about that time, I didnít exactly make some sort of an improvement in the eye-piece, but did change the eyepiece and use an arrangement I made up in the laboratory, but I donít think that was significant. I also reduced the counting of scintillations to a drill which was very necessary, that is, and Rutherford agreed, a count for one minute at a time only, and have a little rest, count again, and so on. And not do more than a certain amount in a day because oneís eyes got tired. Also, a much more important thing really, although the drill helped, was to see only the scintillations that were there and not to imagine scintillations which is very easy to do. But we gradually established the drill, and then I was advised, I donít know by whom, to apply for a research fellowship in Caius, for which I had to submit a written dissertation. That I did under some difficulties because I was extremely busy in the laboratory. It wasnít only my own work. I was doing what I could do to help Rutherford. I keep mentioning that, and they were only trivial matters, but I had to be of some help. That was, in Rutherfordís view and mine, what I was there for.
Weiner:It was the understanding.
Chadwick:It was the understanding between us. It didnít amount to very much in those days. And, very fortunately for me, I was elected to research fellowship. It must have been a very difficult decision for the college council to make because of my age. Normally, one might be 22 or 23, that kind of age, at which one would apply for research fellowship. By that time, you see, I was 30. But it was done, and, of course, for some time then, my future was assured — for the first time. I forget now how long Ö I suppose the period of a research fellowship would be, even at that time, for three years. That would be the normal period, and I think also that it was usual to extend it for another three years, if it proved advisable. But that meant, if I remember rightly, the stipend of a research fellow was 350 pounds, which was quite a bit for me, and of course, rooms in college, and dinners, when dinner was provided, which was, except for a few occasions during the year, every night, if I wanted to take advantage of it. The other thing was that about that same time I had been awarded the Clerk Maxwell Studentship or Scholarship. I donít remember these things. Iíd forgotten about the Clerk Maxwell thing — it might have been earlier.
Weiner:I donít find any reference to it in my notes.
Well, thatís very stupid of me, because that was an unexpected distinction. It was regarded very highly in the university, but at what time that was done I donít remember. What I do remember is a visit to the laboratory from the Secretary of the Department of Scientific and Industrial Research. It must have been 1922, or it might have been early 1923. I donít remember his name. I remember the man very well. He was a civil servant, of course, and why he was coming to the laboratory I donít know. It may be that Rutherford had some grant from the DSIR to build up the laboratory, a grant in addition to what the university could afford, which was very little, because the university was really quite poor, with a great many other departments to look after. But this man, I think, was not a scientist. I think he was a classic, and I think he was a Scot, but I donít remember his name. But he was somewhat alarmed at the burden put on Rutherford. We had at that time not many research students, I suppose there might have been 20, which seems to me a small number compared to what we had later.
Rutherford didnít have much in the way of teaching duties. He had three lectures a week, and naturally he was responsible for teaching, but I donít think he had very much interest in it. But he was obviously responsible for his research students, and this secretary thought this was too much, that some of the more trivial day-to-day matters should be taken away from him. And they offered to, or he offered, or the Department offered, to make the post of Assistant Director of Research, that is, find the money for it. They offered really to appoint me as Assistant Director of Research, salary being paid by the DSIR for some time, I donít know how long, in order to relieve Rutherford of the more trivial duties. And that was the beginning of a great expansion in my duties actually. It began in a small way to begin with, but it did expand, and, of course, that again made a very big difference to me. It gave me a position at the University which I hadnít had before, except as Clerk Maxwell Student. And so, it was about that time, I suppose, that I began with Rutherford on the artificial disintegration. You see he had done this business of looking into the particles of various elements, such as oxygen, which had a range greater than the alpha particles of Radium C. He had used a number of men in the laboratory as observers.
On occasion I had taken part. And he gave an account of those experiments in his Bakerian Lecture, I think that would be 1920, when he concluded from his observations — I think the conclusion was that these particles were helium of mass 3, which were ejected from oxygen and maybe some other gases in some way — but I donít remember exactly what he said. But it was in that lecture, and it appeared to be connected with this conclusion of his that helium 3 existed that he made his suggestion about the neutron. Now, of course, suggestions about neutrons, neutral particles, had been made many times before that suggestion, but not for the same reason. As I said, I had taken part in some of these experiments and, after the conclusion of the experiments, Rutherford always worked out the results immediately and drew what conclusions he could from them, and would think about preparations for the next experiment. Well, I had noticed that in all the experiments in which I took part, there was no evidence whatever for helium 3. I suspected the observations. They had no proper drill at that time. And so, Iím only telling you what I thought about that time for this reason: that it appeared on listening to his Bakerian Lecture that the suggestion that there was a neutron of this particular kind came from these experiments. It didnít. When I began to work with him on the artificial disintegration of various elements, his invitation came really because he thought some chemical work might be necessary, and he thought enough of me as a chemist to be able to do it. But it was also partly because I had established this drill about scintillation counting.
Weiner:The chemical work would be, for example, to detect hydrogen as an impurity?
Chadwick:Yes, hydrogen and nitrogen, I think. But as it turned out, it was quite unnecessary. Before the experiments, before we began to observe in these experiments, we had to accustom ourselves to the dark, to get our eyes adjusted, and we had a big box in the room in which we took refuge while Crowe, Rutherfordís personal assistant and technician, prepared the apparatus. That is to say, he brought the radioactive source down from the radium room, put it in the apparatus, evacuated it, or filled it with whatever, put the various sources in and made the arrangements that weíd agreed upon. And we sat in this dark room, dark box, for perhaps half an hour or so, and naturally, talked. And it was then that I realized that these observations which I suspected were quite wrong, and which proved to be wrong later on, had nothing whatever to do with his suggestion of the neutron, not really. He just hung the suggestion on to it. Because it had been in his mind for some considerable time. He had asked himself, and kept on asking himself, how the atoms were built up, how on earth were you going to get — the general idea being at that time that protons and electrons were the constituents of an atomic nucleus. One could imagine easily enough how a proton and an electron might under certain circumstances get close together, although the presence, the existence of hydrogen as a stable element made it a bit difficult. But how on earth were you going to build up a big nucleus with a large positive charge. And the answer was a neutral particle. And so, it was these conversations that convinced me that the neutron must exist. The only question was how the devil could one get evidence for it, and it was shortly after that I began to make experiments on the side when I could. It was very busy, and left me little time, and occasionally Rutherfordís interest would revive, but only occasionally. He seemed rather to have lost interest as time went on, but occasionally his interest was revived, and we would do an experiment or two together. And not always the wrong experiment. One that I did would have been right enough if Iíd used a different method of observation. It was published under our joint names — but in fact he had nothing to do with it.
Weiner:Which paper was that?
Chadwick:Oh, it was published some years later in the Proceedings of the Cambridge Philosophical Society. Actually, Iíd done the experiments when Rutherford was in New Zealand, and they were published because we were asked to contribute something to the Cambridge Philosophical Society, perhaps for some meeting or other, Iím not sure. And so I produced this. I put his name Ö well, Iím saying ďIĒ Ö I shall be saying ďIĒ many times and I must explain that ďIĒ very often means ďweĒ. It is perfectly true that I did have some — I wonít say responsibility — some influence in what was happening in the laboratory. But I always recognized that the responsibility was Rutherfordís. And now in talking to you like this, I shall say ďI did thisĒ or ďI said thisĒ when it really means ďweĒ, and I must add that this is one of the reasons why I have not written about these times, because I couldnít write it without saying ďIĒ. I couldnít at every point say what Rutherford thought about it because it would only be what I think he thought about it, and very often, it is likely that he had come to the same conclusion himself before I talked to him about it. Iíll mention one or two of the things, perhaps later. So I keep on saying ďIĒ. That was only one of the things to say that ďI did thatĒ when he was away in New Zealand on a holiday.
Weiner:What was the description of that paper? We can look it up later perhaps in the collection, Volume I?
Chadwick:Itís here somewhere. It should be about 1925. It isnít. It was done in the winter of Ď25-Ď26, if I remember rightly, but didnít publish it then. It must be this paper, No. 218 here, ďEnergy Relations in Artificial DisintegrationĒ, Rutherford and Chadwick. Yes, this is the paper.
Weiner:How, in that paper, could you have observed the neutron if you had been able to detect it? You were talking about the 1929 article with Rutherford, which had both of your names on it and in that work you could have observed the neutron if youíd had the proper detection devices.
Chadwick:Well, yes, if I had been looking in the right way. Oh, I did write an article some years back on this thing.
Weiner:At the history of science meeting at Cornell. Yes. I have a copy of that.
Chadwick:It was printed. I was asked to go and give a general talk about the discovery of the neutron. I wasnít very well at the time, and I didnít go, because I couldnít go. It was unfortunate, but I couldnít manage it. At this meeting (in 1929) Rutherford had nothing handy, and so I produced this. It was quite possible he read it. He made no comments. He couldnít have read it very carefully, because he would have questioned, I think, some suggestion I made about atomic nuclei, which was quite wrong. There was more than the mention of the neutron there. There was the experiment Iíd often wanted to do to examine the protons from the artificial disintegration in a thin layer of material — I must have used aluminum — to see if the protons were a homogeneous group or not. They werenít. There were definitely at least two groups. Thereís a picture there of the results. And what I suggested then was just a bit of nonsense, and Rutherford might have questioned it. I canít find it now, but I did say something about the energy relations — you know, the connection between the kinetic energies and the masses as far as that could be done there. What I found was that the protons liberated from quite a thin layer of aluminum by homogeneous alpha particles were not a homogeneous group and at least two groups. I donít think I said that, because it didnít appear. With the methods of scintillation it was very difficult except by prolonged observation to get measurements which are accurate enough. The protons varied over such a wide range of energy that I made the suggestion that some aluminum nuclei might have a greater mass or energy content than others. Well, I donít know whether Rutherford would have questioned that if heíd seen this — I think he would. But certainly if I had consulted Fowler who wasnít so very much in evidence at that time but who was available, he would have pointed out to me immediately that, after all, the nuclei must have some kind of quantum structure, and that while they might be different, they could only be different in the same way as atoms are when some particles are in different levels under certain conditions. However, it was pointed out to me much later by Niels Bohr, which was too late then.
Weiner:It was in print, you mean.
It was not only in print, but we had found that there were these definite groups. And not only that, but there were resonances; and the same thing was found by Pose. I donít know where he was working — in Germany somewhere, Leipzig perhaps, I canít remember. But still that was by the way. Well, what we were talking about really was, I think, how the Cavendish developed. That was what I was thinking about anyhow, and also partly how my duties developed and accumulated in the Cavendish. But I canít tie definite dates to some of those things. It must have been quite early on that Rutherford and I had discussions. He may have had them with others — I donít know — about what we could do as the numbers of research students grew. In the first instance there were quite smallish numbers, but then there were many applications for admissions. And there were two matters, I think, which I should mention. One was whether the laboratory should concentrate on what was beginning to be nuclear physics or have a wider field, or whether in fact we should bother very much with nuclear physics. It wasnít called nuclear physics in those days. But, you see, Rutherford had said some time before in some public address or lecture that the question of the structure of atomic nuclei was one of the most important questions of physics at the present time but that it was very difficult to attack. He didnít see much way of doing it, and if I remember rightly, he said it was a problem which could be left to the next generation.  Well, of course, in my view — I think in his, too, but he didnít say definitely — it was his duty to do it. Who else was there who would go on those lines? And I think I was only saying what he himself thought, but that was the way he went. He did make one or two attempts in other fields, but we hadnít the experience; we hadnít the equipment; we decided it couldnít be pursued any further — that we must concentrate.
But he was attacked occasionally by people outside for doing this. I think I may have said somewhere in some address that he would occasionally come back from London and tell me so-and-so had been criticizing the work of the Cavendish and the line which he was pursuing, and he was a little perturbed by it — perhaps only for the moment. This would be immediately after his visit before heíd thought very much about it. He used to come back to Cambridge between half past five and six, and usually come back to the Cavendish on his way home to talk about what had been happening during the day. And if he didnít come in, then I generally went to his house, which was only a few minutes away, to tell him how the experiments had gone. But then, you see, these criticisms were fresh in his mind and perhaps weighing more heavily upon him then than they would have the next day. But he certainly was a little perturbed at times.
Weiner:The criticism came from colleagues in physics at other institutions?
Chadwick:Yes, I would like to mention names. But in a sense, you see, there was some justification, because it was very difficult indeed to make any progress. One had to jump around and just do what one could. And two things added to the difficulties. One was the shortage of equipment, which really was very serious indeed. That was largely my duty — to provide the equipment as far as I could. We hadnít much money to spend, and I had to be very careful and buy the cheapest high meters and low meters which were available. There was practically nothing to begin with. Pumps which we had to begin with were the old Gaede mercury pump, a few of them, and force pumps, if you know what a force pump is.
Weiner:I know the Gaede pump, but I donít know the other ones.
Chadwick:Well, it is just a cylinder which is evacuated, connected to your apparatus, and then you force a piston down and push out the air which you have collected. But itís quite a small thing, and then turned by hand. It was a very time-wasting business. I suppose the Hivac pump was made in America — Iím not sure. That was the obvious thing to have, and it was necessary. But you could only buy a few at a time. When I say ďat a timeĒ, each year. And I spent the money during the course of the year but saving some up so that at the end of the year I should know better what was needed and then buy it. And then I should know how many people were coming into the laboratory and have a better idea of what they were going to do. Well, that was one thing — general policy — and then the business of providing the means of carrying out the work. The other matter in which I had a hand — a slight hand but still a hand — was the selection of research students. We had quite a number of applications, and we were limited in room, and even more, by the equipment. One thing that I felt we had to do was admit a reasonable number from the Commonwealth, for two reasons. One was that it was very natural for them to apply to the Cavendish. They could not do very much in their own countries. The Canadians could have gone to the United States. Australians and New Zealanders would naturally wish to come to the Cavendish. It was perhaps even more expensive for them to go to the States than to come to England. Also, Rutherford himself came from the Commonwealth. We owed him to New Zealand, and it seemed to me he agreed. Iím quite sure he agreed; he didnít say anything, but it must have been in his mind all the time — and thatís why I say ďIĒ sometimes and it really perhaps means Rutherford. We did have some very good people from Australia and New Zealand and Canada in those days, and they formed quite a proportion of the people we had.
Weiner:What was your annual quota of research students to be admitted? How many new ones would come in a year, for example, in the twenties?
Chadwick:Well, it started perhaps fairly well. The first year there must have been ten or so. But it would be somewhere between 12 and 20, taken altogether.
Weiner:The total number of research students in the lab at one time?
Chadwick:Well, it grew until it came to be between 40 and 50. It began to be very difficult. We expanded a little bit and were able to do that, but that was really a bit more than we could really look after.
Weiner:Now, if the policy decision had been made to pursue nuclear physics as the main activity of the laboratory, did this mean that all the research students admitted were interested and willing to work on nuclear physics?
Their first desire was to work in the Cavendish under Rutherford, and in very few cases indeed did they have any particular problem in mind. Perhaps I should say a little bit about that. Again, you see, I may exaggerate a little my own part in it, because it grew slowly. He generally consulted me about what people were going to do, because in any case I had to provide the apparatus. But we always had some problems in mind. And that is where, as I mentioned before, the Ph.D. degree provided us with some difficulties, because the regulation was that at least two years of research should be spent on the Ph.D. degree course. It was technically three, but a year could be allowed for previous work in research done at his own university. And it was almost a condition of admission that a man from outside should have done at least one year of research at his own university before we admitted him. We didnít want him for three years, but we didnít want to have to start from the beginning. We had to do that for our own men. There might be six or so — of our own Cavendish people from the degree course staying on for research. Well, in their case they could do two years in the Cavendish and a year outside somewhere, at an approved place. But the normal case would be three.
The reason I mention that is that we had to think of problems which would occupy that time and which were big enough for them to get their teeth into and keep them busy and give some kind of positive and reasonable results. That limited us very much. I say ďusĒ, because in the beginning I did not have much say — I had a little. But after I had been made director of research I had a little more say, and later — I canít tell you when it started — our procedure was to jot down during the course of the year various problems that we thought must be looked into. We did that independently. Then in the summer we knew what research students we were going to have, although one or two might turn up later. But we were pretty certain by the middle of the summer what the composition of the laboratory was going to be. Then we sat down together and exchanged our views and decided what could be given, what would provide suitable work for a research student reading for the Ph.D. degree. Well, that meant, you see, that quite a number of interesting things couldnít be done. We didnít have time or equipment actually Ö I ought to add to that, that by that time, you see, there were certain groups in the laboratory. That is, C. D. Ellis would have two or three people working with him. Well, he had certain problems to be getting on with. Well, we would say, ďWhat would you like to do?Ē Two or three people might go to him. Blackett might take one or two — always did take one or two. Ratcliffe ran a wireless group, which had been started by Edward Appleton.
When he left to go to London, it was continued by Ratcliffe, and Ratcliffe always had two or three people. That relieved us of some — not of responsibility, well, to a certain degree responsibility; it made things much easier. But it was always a very difficult thing. And we had, I must say, a difference of opinion about how the laboratory should be run. I thought we were having too many research students, because we did not have the room for them and because also certain things, some points, were not being looked into because they might give a negative answer, but in any case would not occupy a man or sometimes two men working together for a couple of years. And what I wanted to do was to have a few rooms set aside in which various pieces of equipment could be ready for any examination we wanted to make in a hurry, such as a cloud chamber, counting apparatus of different kinds, which only meant a few rooms; but it meant shutting off these rooms from the occupation of these research students. It meant letting in fewer research students. Also, there was some difficulty in keeping the apparatus in order because we had very little technical assistance. And I suppose Rutherford was quite right in saying that we shouldnít do that. Well, anyhow we didnít do it.
Weiner:What was his reason for wanting to be oriented to the needs of large numbers of research students?
Chadwick:To train people in the general attitude of research, not so much in a particular line as to — how shall I put it? They had to do a particular job; but we hoped that they would get the proper attitude to research, to acquire the ability to tackle any problem in physics, not merely in nuclear physics, but any problem that had to come about. And to a certain degree I think we were successful because when the war came many of the radar people were from the Cavendish and had been trained in nuclear physics, but they could turn their hands to quite different things and did it very successfully.
Weiner:This was the experience of the U.S. too.
Chadwick:It was not peculiar to the Cavendish. What we were trying to do was to give them a training in research. That was certainly his attitude. I ought to have mentioned, of course, there was also C.T.R. Wilson, who took one or two people. He didnít work in the Cavendish except perhaps his first year or two, but Iím not sure about that. Then he had rooms in the observatory and a little out station where he did his meteorological work. But he would take one or two — generally speaking, not more than one.
Weiner:You gave what was referred to somewhere as an ďattic courseĒ for the initial training of the research students. Can you tell us something about that?
Chadwick:Well, that was quite simple. Yes, there was a kind of attic which was not very suitable for anything else. If they were quite new to radioactive methods — well, they did a few simple radioactive experiments. The other important thing was to be able to get high vacua, or what we called high vacua in those days. We used to use diffusion pumps to measure the pressure and so on. And then I also put some of them through counting scintillations. The idea was to pick out those who could be relied upon to count scintillations by a method of testing them by recalling simultaneously. It was a method developed by Geiger, and so I used it there to pick out those who would be suitable if required. There were one or two other things, but it only lasted a month or two; and partly also it enabled us to know the men and to form some judgment about their aptitudes and interests Rutherford might go up occasionally, but it was left mostly to me. It was quite interesting to me to learn about the people. You see, towards the end of my time there (I left in 1935), the last few years I had a good deal of responsibility for the research side of the laboratory. Rutherford to some degree was losing interest. There were many other things he had to do. I used to go round part of the laboratory nearly every day. I made it a rule that I saw each man, say, every other day — something of that kind. It was not with the purpose of supervising them really. On occasion I could be helpful to them, because I saw how they were getting on, but one of the chief things was to find out what they needed to get on with the job. I would find that they were hampered by lack of some piece of equipment, which I then proceeded, if possible, to produce. Rutherford used to say that I neednít do that, but I felt that somebody had to do it, and it was my job to do it. And it kept him in touch with what was going on, because we had a regular custom that I should see him somewhere at around 11 oíclock every morning, if he were in the laboratory, and tell him what was going on in the laboratory, what results people were getting and what difficulties there were and so forth. Of course, we would often talk about other things, too, but it was useful to him and to me; and I think it was a good custom.
Weiner:Getting back for a minute to the attic course, what was the size of the group who would be assembled for this instruction?
Chadwick:I donít think ever more than half a dozen. There wasnít room.
Weiner:Only because of the cramped quarters, you mean.
Chadwick:Oh, there just wasnít room. Nor would there be the equipment to spare.
Weiner:This would represent the number of newcomers each year.
Chadwick:Well, some of them, yes. Some didnít need that kind of thing. But our own people particularly would. I mean they had just come through their examinations, and they naturally had fair experience in the laboratories but not of the particular kind of work they were going to do. Well, we didnít know what they were going to do. We may not have decided which problem they would get, because during the course of that month or so of training we might find out something about their aptitudes and interests. We always tried to get them something that would interest them. Of course, quite often I had done preliminary work on the experiments that were given to them — very roughly — in my spare time. Iíd just see that it was possible and that something was going to happen and then leave them to it. But it did mean, you see, that we neglected some things. And it also meant that we missed some things. Iím not sure really that I ought to talk about them. I must talk freely about missing the phenomenon of artificial radioactivity, because it was entirely our own fault. We had thought about it right at the beginning, but I think I said before that practically everybody who worked on radioactivity did an experiment of that kind. But then when we knew about the artificial disintegration of various things, one wanted to know what happened, what was left. And instead of doing the things ourselves, we left a man called Shenstone, who is now in Princeton.
Weiner:Yes, heís just retired.
Heís a Canadian. He was and still is a man to whom Iím much attached. In fact, it isnít very long ago since I saw him. I canít remember now exactly when it was — it isnít very long ago. And he tried to observe the emission of alpha particles. Well, of course, we knew that they werenít emitted particularly slowly. We thought they might be emitted very quickly after the disintegration. I took part once or twice in the experiments with him, and it was a terrifying business — I can tell you. He had a wheel whipping round at something like 20 revs a minute or second. There had been no suitable material in the department from which he could make a wheel which would keep together at such speed, and he went to London and bought, I think, a circular saw. Anyhow it was of some special material which would do it. And this damn thing buzzed round within a few millimeters of the objective of the microscope, and the observerís head was at the eyepiece. If something had gone wrong with that rotating wheel, the microscope would have gone right through your head, and you were in the dark, couldnít see very much but yet could hear the most frightful noise. I wasnít very pleased about taking part in those experiments. Then the other thing was the emission of beta rays, which we gave to a beginner called Massey R. Mudd, whose real problem had something to do with the absorption of gamma rays — I donít know what. He must have published a paper but it was in the early days. As a kind of exercise before going on, we asked him to look at the disintegration of nitrogen.
Well, all he had, you see, was an ionization chamber connected to a pretty sensitive quadrant electrometer and he let the source in and removed it quickly from the neighborhood — somebody would run away with it — and he measured if there was any ionization left. Well, of course, there was because the ions hadnít all recombined. He could measure that — the remaining ionization and the disappearance as the ions recombined. There was nothing left over because the apparatus wasnít sensitive enough. And, you see, the great mistake was Ö I donít know whether I could have done it with a point counter, which was available; Iíd done a lot of work on various forms of counters in the hope of finding something that would give a magnified result proportional to the initial ionization. But I never did. I did indeed try a valve method, but I failed, partly because of the conditions in the Cavendish, which were not conducive to any sensitive experiments with valves, but chiefly owing to my own ignorance and lack of equipment. But the greatest mistake of all is when Geiger and Muller invented what is now called the Geiger counter, which is really the Geiger-Muller counter, and he sent me a couple of them. And instead of going back to the question of artificial radioactivity, which I certainly had forgotten all about, we used them for trying to find the neutron.
Weiner:Which was productive in itself.
Chadwick:Yes, but, you see, it was wrong; it was looking in the wrong place.
Weiner:You mentioned the other day about Gamow and the fact that your attitude on artificial radioactivity was partially influenced because you had listened to some explanation of his. I wasnít clear what you meant by that.
Chadwick:Iím not clear myself now. I thought I was at the time I mentioned it.
Weiner:Well, apparently there was a certain theoretical conception which influenced you.
Chadwick:Yes, it was partly connected with the view of quantum mechanics that the electron outside the nucleus spent part of its time in the nucleus. It was partly connected with that, but Iíve forgotten now exactly how the argument arose. It had something to do with the stability of the nucleus left after the disintegration, and Iíve forgotten. I got mixed up anyhow. The real trouble was, as I mentioned more or less casually there, that I never really had thought deeply enough about the properties the neutron would have. I had always an idea that it would produce some ionization. Now, if I had talked to Niels Bohr about that, heíd have put me right immediately. But he wasnít available. There is one of the great regrets that I have had, that I never visited his laboratory in the earlier days. I did later — I canít remember when now. I doubt whether I was ever there even for a short visit before the war.
Weiner:There are some letters in the Bohr papers, one in particular, inviting you to one of their spring conferences, and you were unable to attend. But he wanted particularly for you to discuss the neutron work in Ď32 after the announcement and you were unable to make it and indicated you would try the next time around. But for one reason or another you didnít get there.
Chadwick:Well, you know, I was rather busy.
Weiner:I gather, from everything you have said.
Chadwick:I didnít have much time. And it wasnít easy to snatch a holiday. Very honestly, I would have to interrupt work at an almost critical time. If I wanted a holiday at all, it had to be arranged beforehand. I donít want to exaggerate, but 40 or 50 research students are apt to keep one a bit busy, and it was my job. I must say something about that in a minute before I forget. Rutherford always said that I overdid it, but I was quite sure that I didnít, because, as I said before, it wasnít that I wanted to give them advice, or thought that they needed it — they did occasionally, and I was able to be helpful now and again on the problems — but there were difficulties about equipment all the time. I hesitate to mention any particular instance, but I will mention one because I was reminded of it by the man himself. I had forgotten. That was Mark Oliphant. And he was in real difficulty because he hadnít got the equipment to get a proper vacuum. He wanted a high vacuum. I said, ďWell, Iím sorry, there isnít oneĒ. We had a bit of a talk, and I went away, and, realizing his difficulties, I saw that he really couldnít get on without a high vac, and I went round the laboratory and somehow or other I got hold of one. I think, as a matter of fact, it was one I kept for Rutherfordís lectures. But I took a chance, and I had it put on Oliphantís bench. He had gone to lunch almost in tears; so he told me much later. He came back and all was well. Well, it was that kind of thing that made me go and see everybody as often as I could, and I said alternate days; well, it might be three days; occasionally, if there were real difficulties, I might go and see a man every day. I donít think it was a waste of time. We regarded it as part of our duty not merely to get results but to train people.
Weiner:You indicated a certain reserve in Rutherfordís attitude regarding funds and asking for funds, especially when it came from sources that he thought he would have to be accountable to. For example, in our discussion the other day you mentioned you remembered a memo that you prepared on what the cost was per student. Can you go into that a bit?
Chadwick:Oh, no, I couldnít at this time. You can guess roughly what it was. The grant in 1928 — I know this because I looked it up less than 20 years ago; itís all published, you see, in the financial statements of the University — was about 200O a year. Well, if we had 40 research students it comes out to 40, but some of that money was spent on teaching equipment. But that brings me to a point which I was going to mention a few minutes ago which throws some light on Rutherfordís attitude. A research student entered for the Ph.D. course had to pay fees — Iíve forgotten what they were, but he had to pay certain fees to the University. Now, part of those fees were paid to his supervisor for his work in supervising the work of the student. In the case of the research students who came to the Cavendish, those fees were paid to Rutherford. I donít think that anybody else received a fee. I think he took all the fees. But not for himself. He put them into the laboratory fund. And I remember pointing out to him on one occasion that really my stipend was paid for by these fees from the research students. It didnít quite meet it but it was near enough. It might be 500 a year. And Rutherford would have been perfectly justified in putting it into his own pocket, but would never — well, I wonít say it never crossed his mind — but he would never under any circumstances have done that.
Weiner:How many sources of funds from outside grants? — individuals who may have wanted to make a gift? Solicited and unsolicited. For example, was there any active attempt to raise additional funds other than that made available by the University?
Chadwick:Only in one case to my knowledge. I told you about that.
Weiner:But we were talking without the tape.
I know. Iím not sure that I ought to mention it. Well, I think I might, and then weíll see later on what we do with it. One reason why Iím reluctant to mention it is because nobody else knows about it. You see, Rutherford never said a word to me. I thought he might have said a word to a man whoís still alive, Henry Thirkill, who was a lecturer in the Cavendish, and who looked after the Cavendish accounts for Rutherford, because every laboratory had to prepare its accounts for the University, and it was a drudgery which Rutherford shrank from. It was the kind of thing he wouldnít do, but Thirkill did them for him. And I thought he might have mentioned this to Henry Thirkill. A few years ago I asked Thirkill. He never heard about it. Well, Iím quite sure he wouldnít have told anybody else. But I told you what happened to me. This must have been in the early 1920ís, because Iím pretty sure I was living in College, and I didnít live in College after October 1925. I got married in the middle of 1925; I must show you a picture. So I think it was before that. It was an occasion on which the Master had been dining in College, as he did now and again. There hadnít been many people dining. I suppose it was probably during vacation or summer, you see. A few people had been dining, and we were quite suddenly alone. He said to me, ďWhy didnít Rutherford ask for the money Iíd arranged he should be given?Ē I said I knew nothing whatever about it. That was the first Iíd heard of any money from outside. So he told me. He was very upset about it. He was a very remarkable man, H. K. Anderson. He was the best master Gonville and Caius College had had since the days of John Caius, in my opinion. He was a man of such quality that I was slightly in awe of him. Oh, he was a very great force in the University in his day, in the background. He could not do anything publicly. He never became vice-chancellor, for example. He could with the greatest difficulty make a speech at a school. He did it once and was thoroughly ashamed of himself. But, as I say, he was a very remarkable man. Anyway, then he told me this story. He had a very great admiration for Rutherford; and, as I told you earlier, that is how I came to Cambridge, and Iím quite sure also how really the College Council brought themselves to make me a Fellow at the College at my age.
Iím quite sure it was partly, at any rate, to help Rutherford — on that occasion, too. But he was a fairly rich man, came from a well-known shipping family. He had rich friends. At least one brother was head of the Orient Line. And he had persuaded them to give 2000 a year collectively for Rutherford, for his own researches, to use as he wished. But Rutherford had to say that he needed this money, and he didnít. He said nothing — didnít even explain to Anderson why he hadnít said he wanted it. And, as I say, so far as I know, he never mentioned it to anybody at all. He may have mentioned it to his wife, but I donít think so. I was going to say I think she might have told me later on, not at that particular time. But there were, I think, two reasons why he wouldnít ask for it. One was that I believe he was essentially a very modest man. I think he was always surprised at what he had done. He gloried in it. Oh, he used to enjoy anything written in his praise. He or I would come across something, say, in German publications he didnít read. He didnít know German at all well. He only knew a few words. So he would ask me to translate them for him. And he enjoyed it. But one word which he enjoyed particularly was ďBahnbrechendĒ (pioneering). When that came, he would repeat it and glory in it. But nevertheless Ö I knew him fairly well, you see, because it wasnít only in the laboratory that I knew him. I knew him at home. And on at least three occasions I had spent holidays with him and with Mrs. Rutherford, and once with him alone when she was unwell and couldnít come.
So I felt that I knew him in off-guarded moments when he was not being the great physicist, you see. I told you of a later occasion when he had asked me about the radium room where we collected the emanation and made preparations of active deposits; and occasionally I did a few other things when it was necessary in terms of chemistry, which was sometimes necessary. And so I said, ďCome along and have a lookĒ. He didnít. He hadnít penetrated there for a very long time, because it was right at the top of the building; there were lots of stairs. He was not old, but he was a heavy man, and he had a bad knee; so that sometimes staircases were difficult for him. Iím only just explaining why he hadnít been there for some time. And then we had this couple of hundred milligrams of radium which had been lent to him by the Austrian government when he was in Manchester, which he had later arranged to pay for; and we had another lot which had come from some government department. It was material which had been collected from gun sites and such things used in the first war, and besides radium it contained some mesothorium, too. It helped us. Altogether I suppose we had getting on toward 350, 400 milligrams — Iíve forgotten exactly. But anyhow we went up. He saw everything. You see, part of my duties was to allocate radioactive sources amongst the research students. And, as he knew, there was always a much greater demand than I could satisfy. He just asked a few questions as to how things were at that time, and so I said it was still very difficult. We could do with a great deal more than we had. I said, ďWhat a pity it is that somebody didnít give you a gram of radium as the women of America had given to Madame CurieĒ. We were then just coming down the staircase, and he stopped, patted me on the shoulder and he said, ďMy boy, I am damned glad that nobody ever did. Just you think, every year I should have to think of the import of what I had one with a whole gram of radium, and I should find it impossible to justify itĒ. Well, I donít know. That, I think, was modesty. It was also a reluctance to be responsible to somebody outside the laboratory. Well, of course, in a sense he was responsible to the University, but that was just a general responsibility — there was nothing formal about it except the preparation of financial statements. It is the habit in some departments of the University now to make a kind of annual report, but I donít think it was ever done in the Cavendish. I donít remember seeing one.
Weiner:You mean a published annual report.
Chadwick:Well, a circulation amongst the University. It wouldnít be published outside. And the financial statement was more or less a kind of internal document. The University also prepared full accounts in which everybodyís stipend was stated and all kinds of expenses — postage and telephones and that kind of thing. The financial statements are really very full.
Weiner:Thatís something I should study.
Chadwick:Iím sorry I donít have any now.
Weiner:Iím sure thereíll be a full set in the library.
Chadwick:Every college has them.
Chadwick:Well, I was going to say something else about Rutherford while I think of it. And that is that he always showed a great deal of consideration — in his own way — and interest in — his students. I must tell you one experience of mine. It must have been fairly early in my time in Cambridge, a year or two years after 1919 — that kind of time; I donít remember exactly. But there was the Cavendish Physical Society.
Weiner:That was my next question: The Cavendish Physical Society. So you have come to it.
Chadwick:My recollection is that the session opened with an account by Rutherford similar to what you have in the United States when the President makes a speech on the State of the Nation to Congress. Itís very much the same kind of thing. I think we met every week.
Weiner:I saw a reference to a fortnightly meeting.
Chadwick:Fortnightly, was it? Well, that must be right. My memory is vague on these things. I gave a paper on one occasion. It was on my own work — whatever it was, I donít remember. I didnít do it well. In fact, I did it rather badly. And Rutherford made no bones whatever about his opinion on it afterwards. He told me Iíd done it badly. In effect he said, ďThat wonít do. I will find an occasion for you to give another addressĒ. And he waited for some time. And he asked me to give a report on some work which had been done in Germany. It wasnít nuclear physics. It was some x-ray work, some particular interest — Iíve forgotten exactly. That was to give me another chance to rehabilitate myself, give me some confidence. And he was quite satisfied on that occasion. I did do it quite well, and he was quite satisfied. But many people would not have put themselves out in that way. But he did take an interest in people. I wouldnít call him kind; I donít think thatís right. He was kind, and he was considerate, but in a somewhat peculiar way, because in his general manner he was rather hearty and robust, and one didnít see at first what was really behind it all. I can give you other instances. I remember I was dining in Trinity one night with somebody else. I often did dine in Trinity, perhaps with Ellis or some other fellow, and Rutherford was there, and we were sitting around. We werenít actually talking to him at the time. And a stranger came in who was a guest of somebody. His host was not there. Obviously he didnít know anybody present, and he looked very uncomfortable, and nobody said a word to him except Rutherford. Rutherford saw that he was uncomfortable and strange and got up, introduced himself and made him feel at home. That was typical of him. It was a somewhat unusual thing to find in Cambridge.
Weiner:You mean in the colleges themselves. But what about in the laboratory? What was the atmosphere in terms of personal relationships?
Chadwick:Oh, quite good in Cambridge. In Manchester — of course, I was very young, and I was afraid of him — I think the only adjective I could use was that he was fairly tough. But after coming to Cambridge, he mellowed considerably. It was also a much easier life. In Manchester he lived a couple of miles away from the laboratory, and he would travel in by tram, electric tram. And, of course, he had his lunch at the University as a rule and would go back by tram in the evening. But here he had a house — in fact, it belonged to Gonville and Caius — Newton cottage, just on the backs. And it was a very easy, pleasant walk to the cottages all round by Silver Street to the laboratory. And he could just walk home for lunch. Whenever he wanted to he could go dine in College. I think he did fairly regularly, once a week at that time. I really donít remember properly, but everything was much easier for him, and he enjoyed that. And, of course, he was getting older, and he was generally recognized as the head of physics in this country, and of course it was easy for him to go to London. In all kinds of ways his life was much easier in Cambridge. I must use the same words; it mellowed him.
Weiner:Still his attitude in the laboratory would be one of a sense of mission in terms of training people and getting on with the job. He would tend still to have high standards in terms of the goals of the different groups.
Chadwick:Yes, of course, for many years he was a little disappointed, because it was so very very difficult to find out anything really important about the structure of nuclei. He had published a paper on the structure of nuclei about 1927.  It was before the publication of that book anyhow, and I remember we were working together; I was working with him at the time; he talked to me about it. But I had not much opinion of it. It seemed to me to have very little, to put it mildly, significance. He was rather annoyed with me at the time. But when it came to writing that book — that is Rutherford, Chadwick and Ellis — I wrote that part, and of course I had to say something about this paper that he had written, and I said what he suggested. Then I made some comments on it, which werenít very complimentary.  It was one of the parts that he read. I donít think he read all the book — I donít know — but he read that. And so he tackled me about it. He said, ďWell, you donít seem to think very much of my theory of the nuclear structureĒ. And I said ďNo, I donít. Itís artificial. It wonít explain some of the observationsĒ. And I think I said at the time, ďIt makes no mention of the neutron, which must be.Ē He had perhaps forgotten about it to some degree. ďIt must be an important part of the structure.Ē ďWell,Ē he said, ďif thatís what you think, we better leave it as it is.!í And he didnít alter a word.
Weiner:What was the nature of your collaboration with Rutherford and Ellis on the famous Rutherford, Chadwick, Ellis book?
Chadwick:Iím not sure what you mean. We just wrote it — thatís all.
Weiner:Were parts of it divided or was it a question of revising Ö?
Chadwick:Oh, yes. Rutherford didnít have very much to do with it really. He only felt that it was time that his old book should be brought up to date. I suppose there was some urge from the Cambridge Press. I donít remember that. He wrote the early part, a kind of introduction — I shall have to look at it — about the disintegration theory, which was not very different from what had appeared in the older edition. There may have been some new things in it, but Iím not sure that I didnít put them in, things aboutÖ ďBranch ProductsĒ — I presume a good part of that would be new. Well, Iím not sure whether he wrote that or whether I did. I think a bit of both perhaps. This is a revised edition. 1930 is the date of publication.
Weiner:You must have started working on it substantially before then. When did you begin?
Chadwick:I can tell you that. At least I can tell you when I began: the autumn and winter of 1926, late autumn of 1926. I remember that very well because I married in 1925, and for the first year I took a furnished house which had been built by a friend who had gone to Edinburgh. I then proceeded to have a house built, and it was supposed to be ready by October 1926. Well, it wasnít. Part of it. And it had been promised in the contract. And so we had to live in another furnished house. We had to find one. As it happened, it belonged to the mother-in-law of the friend from whom I had rented the first house. She didnít use it in the winter; she lived somewhere else in the winter and only occasionally came up to Cambridge in the summer. It was a cold winter, and it was a very drafty house. There was a door between the drawing room or sitting room perhaps I should call it — reasonably sized, and the garage. But it didnít fit very well, and the wind came through. There was no central heating. I was busy in the laboratory, and the only time I had to work was late at night, and it was so cold that I had to put a little table in front of the fire after my wife and the cook general (as we called them in those days) had gone to bed; I put this little table in front of the fire with an overcoat on and sometimes with gloves, and wrote what I could before about 12 or 1 oíclock, that kind of thing. It was done in intervals. Thatís one reason why it took such a long time. But I did one part and Ellis did another. One or two people helped in other ways. Thereís a whole chapter (I donít know whether it is mentioned) in Ellisí section that was written by a man named E. J. Williams, who was then in the laboratory and who was a very able man and made a study of that particular kind, that particular subject, and presented it in rather a different way from the usual way.
Weiner:This was just about the time when the new quantum mechanics had been brought to a successful development, a successful conclusion. Did this in any way affect the writing of the book, the interpretations and the types of material that would be included?
Chadwick:It was a bit too late. Thereís some mention of it, yes. But I think it was only here and there and partly in the appendix.
Weiner:As I recall, it was just on the brink.
Chadwick:Well, yes. The thing to do is to look up Gamow, isnít it? And see. Gamow. There are quite a number (of references) page 177. Oh, yes, it is included here — the Gamow and Gurney-Condon business.
Weiner:But it wasnít the fact that these new developments changed the situation that made the new edition of the book necessary. In other words, that wasnít the motivating force for writing it?
Weiner:As you indicated, it started before those papers came out.
Chadwick:Yes, it was simply because the old edition was so much out of date.
Weiner:Thereís a whole series of questions that I have that relate to this feeling — not of despair but, as you expressed it, of Rutherford wanting to probe the structure of nuclei but not seeing the possibility of doing it, and at the same time being criticized on the outside because he was directing his laboratory along the general line of nuclear physics. One of the things I would like to know is when the idea that electromagnetic forces could not hold the nucleus together and that stronger forces were required really took hold: the idea, for example, that was later developed, of the potential barrier and the potential well. When was that clear in your mind or in Rutherfordís mind or to both of you?
Chadwick:That was clear about 1921 or Ď22. But we had no explanation of it. I put it this way: Any idea one might have about the structure of the nucleus — particles had to be held together somewhere. So that in addition to the repulsive force between the positively charged particles, there had to be an attractive force somewhere. And I played around with various forms of the force with an attraction varying as the inverse fourth power of the distance. And I remember I had to brush up my mathematics a bit in order to solve some of the equations. And it was also clear, I think, in Bielerís mind, too. I remember our making lantern slides showing the potential well and the peak and so forth, and they were used in lectures. They may exist still — I donít know. Theyíve probably been thrown away by now, but they did exist. But that was quite early. But, you see, one didnítÖ It was bound to be like that, but how as it like that? We couldnít find out. In a sense itís that kind of thinking that led Rutherford to suggest the existence of the neutron. He didnít follow it up because of the great difficulties. I was off and on for eight or nine years making experiments, in some of which Rutherford took part when his interest revived. But while one felt that it had to be that way, it seemed quite impossible to get any evidence. We were always looking for something of the kind, but we didnít get it. Oh, no, the idea of the potential well was certainly clear to Rutherford and to me and possibly I should think to others as well. But we certainly used that; and, as I say, I prepared these lantern slides to show it.
Weiner:When the Gamow, Condon and Gurney papers came out in 1927-28, did they signal a rebirth of interest in the nucleus and in nuclear physics?
Chadwick:Itís very difficult to say that. One began to have some inkling of how things might be, but I donít know — I donít think it was much more than an inkling. It explains immediately some things which had been a little bit difficult, but it left completely untouched the question of the structure of the nucleus, and nothing was ever said about that.
Weiner:Do you remember discussions at the Cavendish specifically on these papers?
Chadwick:No, I donít remember. Iím not quite sure whether I remember Gamow giving a paper to the Cavendish Physical Society or not. Somebody certainly did. It was as a result of that that John Cockcroft calculated the probability of the penetration of protons into the nucleus, which led him to the experiments. Now, of course, many years before I had suggested to Rutherford that we should build apparatus to produce a million volts or so, but I hadnít any idea of that kind of thing happening.
Weiner:What would have been the purpose then of building it?
Chadwick:Just to see what would happen. You donít always have to have a definite purpose in mind. You donít know whatís going to happen until you try it. Later on — well, it couldnít have been much later on (I thought) — if there was a neutron, if it was made from a proton-electron, why did the hydrogen atom exist? Why? I thought: Perhaps if one could make some protons of high energies — I was only thinking of, say, 200,000 volts — and bombarded the electrons, which were held tight to the nucleus, the protons would get a bit nearer than it otherwise would, which is perfectly true. But I wasnít thinking of a proton going into the nucleus, Of course, that is what I should have found. I shouldnít have found what I was looking for. I should have found something else altogether. I didnít do it because there wasnít the apparatus available. And, in any case, there wasnít the money; and if it came to making high voltages, why then I wasnít the man to do it. But we had had in mind the question of accelerating things with various devices, to accelerate particles. I think Walton published a paper in which he described some methods of accelerating particles. I donít remember the date of that.
Weiner:When was it that you raised this with Rutherford and what was his reaction at the time? You gave me a lot of good reasons — resources and so forth. You were more aware of these problems than anyone else in the laboratory, and yet you suggested it. You probably saw a way of overcoming these limitations. If it was a matter of priority, then Rutherford apparently didnít feel that way. Is my interpretation correct? In other words, when you suggested to him to build a relatively high-energy device, that was the end of the discussion, because he objected to it or he didnít see the need for it.
Chadwick:Yes. Well, I donít want to say anything about that time. There was a short period when things were a little unhappy between us, and I donít want to say anything about it. I did try using high-frequency discharges with odd materials that I could pick up around the laboratory to produce high voltages — you know, kind of tesla discharges and such things. But there wasnít the equipment available. And to be quite frank, I wasnít the man to do it. I was trying to do it all by myself, and I failed. It was all on a very small scale, and in order to be successful on a big scale I should have needed a good deal of equipment, because the loses were so big; and if youíre working on the scale I was, the losses were so great that I couldnít possibly expect anything; and I could not get any bigger apparatus. Thatís a period Iím unwilling to talk about.
Weiner:This is the Ď20ís youíre discussing, though; it carried over somewhat.
Chadwick:Yes. Oh, it all came right in the end. But, in fact, Rutherford was not well at the time, and it affected him, and perhaps I was a bit awkward — I donít know. I donít think I was really, but he was definitely unwell, and for the time we parted company, but we joined up again.
Weiner:Youíre referring to the time you were at the laboratory before 1935.
Chadwick:Oh, yes, in the early Ď20ís, in the Ď20ís some time.
Weiner:I think we will stop, as our timekeeper has indicated. But let me ask a final question. Were you aware of the work of Tuve being done in Washington with tesla discharges, creating high-voltage discharges with a tesla coil? This was the late Ď20ís when he was doing some experiments.
Chadwick:No, I wasnít. I may have been at that time. But I think the time Iím referring to was before this. If Tuve had published anything, I should certainly have read it, because I may have met him once — I donít remember — but Iíve always had a very high opinion of his work. He is to me an extremely able experimenter.
Weiner:He started to come to the Cavendish for a year but was offered the opportunity of doing high-voltage discharge work at the Carnegie Institution in Washington. I think it was by 1927 that he developed these very high voltages. He worked with Breit.
Chadwick:Iíd forgotten about that.
Weiner:Well, letís stick to our timekeeperís judgment.
Chadwick:As you wish.
Weiner:Weíre just renewing for a bit. I asked the question: Was there any night work at the Cavendish?
Chadwick:I donít remember any. It is just possible that on one or two special occasions, that might have been. But I donít remember any. The rule was that the laboratory closed at 6 oíclock and then you went home, whatever home was. You would normally be a fellow at the College; otherwise you couldnít exist in Cambridge, because university stipends were very low. You would have dinner, talk about other things, or you might have teaching, college teaching, in the evening, as I had and most people had, most of the staff, and some of them during the day, because there were not only university lectures, but the main teaching in the early days was college teaching. Take the example of Charles Ellis. There were very few lectures in the Cavendish which were of much use to him. He had college supervision, but I think most of his work — I mean for his degree course — was done with Basil Schonland, who was also reading for the tripos. They worked together and read books together and discussed things together. But then your supervisor was the man for whom you would read essays on some subject he had selected and discuss any matters that you were unclear about or wanted to know about. And the bulk of the teaching in those days was in the colleges. Thereís more teaching in the University now than there used to be, much more; but there is still college teaching, which can be quite valuable, because you have a personal contact. The general rule was that you would only have one man at a time for supervision or perhaps two, but that had to be relaxed at certain times when the load was heavy. Iíve forgotten why we turned to that.
Weiner:The reason we resumed was because we were talking about night work. But that relates to a lot of other things.
Chadwick:Yes, we closed at 6 oíclock. Well, the man responsible for closing the laboratory and seeing that everything was all right and locking it up was a kind of steward — he was the head of the workshops, a man called Lincoln, a very fine man. He had started as a boy about so big in the Cavendish, and they had to make a platform for him so that he could reach up to the lathe. And he would come round and tell people: ďTime to goĒ. I remember I was talking to one man, a New Zealander, who was still working away, and he was turning the handle of a force pump, and Lincoln came along and just looked at him, indicating it was time to stop that and to go home. Burbidge, turning the handle, said, ďWell, can I play any tune for you, Mr. Lincoln?Ē And Lincoln said, ďYes, ĎOme Sweet ĎOme, if you donít mind, Mr. BurbidgeĒ.
Weiner:Thatís very good. Was this Geoffrey Burbidge, the one who is the astronomer, astro-physicist now?
Chadwick:No, heís in New Zealand. I donít know what has happened to him.
Weiner:I see. Well, letís end on that, since itís almost 6 oíclock now.
Chadwick:Oh, no, I donít know of any night work. I donít know how you would get in.
Weiner:You could crawl in through the window.
Chadwick:Oh, but all the gates would be closed, and the windows would be, I should imagine, protected by iron railings.
Well, on that note weíll play ďĎOme Sweet ĎOmeĒ.
E. Rutherford, "Atomic Nuclei and their Transformations", Proc. Phys. Soc., 39 (1927) 359-372. Also: The Collected Papers of Lord Rutherford, Vol. III, 164-180. This was the 12th Guthrie Lecture, delivered Feb. 25, 1972.
Rutherford in previously cited reference said that he said this in a discussion of atomic structure before the Royal Society in 1913.
Rutherford, "Structure of the Radioactive Atom and Origin of the X-Rays", Phil. Mag., 4 (Sept. 1927) 580-805; also: The Collected Papers of Lord Rutherford, 181-202.
Rutherford, Chadwick & Ellis, Radiations from Radioactive Substances, (New York, 1930) 327.