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In footnotes or endnotes please cite AIP interviews like this:
Interview of Philip Dee by Charles Weiner on 1971 November 5,
Niels Bohr Library & Archives, American Institute of Physics,
College Park, MD USA,
For multiple citations, "AIP" is the preferred abbreviation for the location.
In this interview, Dee begins with a brief biographical discussion, before speaking in detail about entering Cambridge and his experience with the tripos exams. His discussion of his early scientitfic career focuses on his training under C.T.R. Wilson, and his work with James Chadwick, Sir John Cockcroft, Ernest Rutherford, Mark Oliphant. The conversation then emphasizes his work with photographing and detecting events in nuclear physics, and the development of cyclotrons in Cambridge laboratories. Throughout the interview, Dee discusses various aspects of working at Cavendish and the people there.
As I indicated earlier, I would like to start with a brief description from you of your family background and schooling.
Well, I wish I'd known you were going to be as personal as that. I would have to pause to think what I would say. This will really have to be spontaneous. I had no conception that you would be asking that sort of question. Do you really want me to go right back to the beginning?
To understand who you are —
— and how I got here, shall we say, roughly? You want to know that? Well, I was born in a village in Gloucestershire called King’s Cross, and my father was an elementary schoolmaster. I had two brothers one younger and one older than myself, and my father was the headmaster of an elementary school, which is the lowest level type of school there is in the country. I was a pupil there until I got a scholarship to a secondary school, Marling School in Stroud about a mile from my home, and I went there, and from there I took a number of examinations and I think I can truthfully say that it was a conception entirely of my own that I would like to go to Cambridge, and this arose I think largely because, in our house there were lots of books on elementary science. In particular I remember the history of the candle by Tyndall and things like this, and I was very interested in a boyish way, in science. I used to read about atoms. I read as a child about J.J. Thomson and this sort of thing, and I decided Cambridge was the place that I would like to go to. Well, this was really an unthinkable thing for anyone in my environment then. Nobody in my school had ever tried to go to Cambridge, and I certainly didn't have parents who were capable financially of sending me there. But anyway I made the necessary moves in this regard, and I had two wonderful teachers at school, one a physicists the other a chemist, and they encouraged me to try and sit a Cambridge Scholarship, which I did and which I got.
Had you had any science classes in your school?
Oh yes, quite a bit. You know, I took all the normal subjects associated with things — the sort of school certificate examinations, the inter-university boards certificates, and things of this kind, which you take at different ages. I took these rather young, and I — well, I really had a terribly good chemistry master. I started intending to be a chemist, and really I think this was a man named Pearson (I know nothing about him now), but to me he was the tremendously formative person, in my life, because he played on my scientific interests and vanity. If it isn't irrelevant, I’d tell a story which I think is rather a good one, as illustrating what I think good teaching is. He turned up at school one day with a tin can which contained what apparently was a lot of sludge, and he maintained that this was scrapings off the floor of a sulphuric acid plants and in my innocence, he showed me a periodic table which was so old that the element selenium did not appear on it, or if it did it was regarded merely as being there hypothetically, and he suggested that this compound might be in this sludge, that it would be a natural place to find it, and he suggested that I embark on a process of trying to prepare compounds of selenium by working on analogy of what you might expect from knowing about sulphur. And I did this. I spent a lot of my holidays doing this, and got to making quite a considerable number of selenium compounds which for me were discoveries. You know, I made selenium trioxide and copper salinate. I did transformations of one to the others and each of these transformations used to yield an atomic weight for this element, of course, and things of this kind.
Where did you work?
In my school chemistry laboratory. A secondary school.
It was open to you during hours when you wanted to?
Yes, and at the school I was able to be doing quite a lot of time at this sort of thing. This was one of my great interests.
How old were you at that time?
I suppose of the order of 16, 17, sort of thing, because I think I took my scholarship for Cambridge when I was 17. I think so. Well, anyway I made a lot of these and I was very proud of these, and I even had a little cabinet in which I had them indexed, and I took them to Cambridge and showed them proudly to my supervisor. This was the first time I discovered the whole thing had been a swizzle, and the chemistry master had known perfectly well about all these compounds, you see. At any rate, this kept me very busy as a young man, and I think it was a grand way of learning chemistry, much better than doing hypothetical problems. Well, then I went to Cambridge.
Did you take an examination for Cambridge?
Oh, an open scholarship. I had to because my parents couldn't have afforded to send me to Cambridge.
In those days, they were...?
In those days they were of the nature of the present state scholarships and things of that kind, but not state controlled. They were scholarships which were given by the different colleges at Cambridge. Each college at Cambridge has of course big endowments, and they provide money for a limited number of scholars, which forms perhaps 10, 20 percent, I don’t know what percent of the total number of students there.
Do you have to qualify in a certain sense in order to be able to take the examination?
I can't remember. I should think anyone could take it. Certainly there would be nothing other than some academic qualifications. It may well be that there were no academic qualifications. Because after all, they set the papers, and if you couldn't answer the questions you wouldn't get a scholarship. It would be as simple as that. But I know I went from Gloucestershire up to Cambridge, the first time I'd ever left home in fact, and sat this examination, and it was quite forbidding. I wouldn't like to give the statistics but my guess would be, there would be two or three hundred people trying to get such scholarships. I don't know what the total number would be, probably 10, 20 something of that sort.
Selected out of that.
Oh, it's very competitive. And the amounts of money weren't very big, of course, but once you got one of these, your county educational authority then came through with a little money and so did the school. I think altogether I had — I don't know the precise figures — but probably three sums of the order of 50 pounds each, I should think, a total of about 150 a year, on which I went to Cambridge.
Did you have an option to take a specific type of exam?
Oh yes, you took it in specific subjects. I took it in physics, chemistry and mathematics, those three subjects, although you could have done a scholarship in mathematics only, which would have been much harder, — but there was a mathematics for science candidates, and I’m pretty sure the exams were in those three subjects. Sure to have been, because chemistry was my love at that time rather than physics, I suppose, as a result of this chemistry master. Well, after I'd been at Cambridge a couple of years or so I decided to — the chemical experimental work struck me as incredibly drab, especially the organic work and also of course the Cavendish had J.J. Thomson, and although nuclear physics hadn't started at that time, atomic physics, atomic structure broadly had. I mean, nuclear structure hadn't started, but you know the conception of the planetary nuclear atom, this sort of thing was there, and this was exciting to a child.
What year was this that you went to Cambridge?
You know, I wouldn't be sure. I would think ‘23s something like that, perhaps ‘22, because I'm pretty sure I took — I'd have to look this up. I’m not dead sure. Wait a minute, I could work it out. I would think I took part 2 of the tripos in 1925, ‘26. That would be my honors year. It would be 1925-26. But I lost a year. I took four years rather than three because I was a pneumonia addict in all these early years, and I used to have successive bouts of pneumonia, so I lost a year through having pneumonia the first set of exams that came up, but thereafter it was all right, and I took part 2 of the tripos I’m pretty sure in 1926.
What college was this?
Sidney Sussex. But by this time I had moved of course. I did part 1 of the matri-science tripos which was physics, chemistry and mathematics, but during the course of that, as I say, I began to decide that physics was a very much more interesting subject than chemistry, and so I abandoned the idea of doing chemistry part 2, and I did physics part 2. 1 started actually doing four subjects — physics, chemistry, mathematics and mineralogy. This was forced upon new students when I went up to Cambridge because students weren't getting good enough marks in mathematics to make up the aggregates which you had to have for a first class honors degree. You had to have a certain aggregate in three subjects, and students were not getting this if mathematics was one of the subjects, as the math marking was low. We were all made to take up a fourth subject and I chose mineralogy, and I got on swimmingly with this the first term when it was all crystallography. But in the second term, when I was taken into a huge room and shown thousands of minerals and told that I would be asked during an exam to identify these minerals with their sources and so on —
— physical and chemical properties?
Yes. Well, frankly, I walked straight out, because one of my great worries all my life is that I’ve never had any memory, that my only hope of coping is by understanding a generality and being able to apply it. Whereas I could do this quite reasonably in crystallography, where you sort of calculate things and do things, I knew that I would never succeed at all in meeting these requirements in mineralogy. So I literally walked straight out of the first class. In the second term, where this requirement was said, I went to see my tutor and I told him of this defeat that I had, and that it was hopeless, and he then jut decide do the only thing to do would be, I'd have to get the necessary marks in mathematics, you see. So he used to give me tutorials in mathematics, and this turned out all right in the end. So that was it and I took part 2 of the tripos. Well, now, is this about the sort of thing you're wanting? Shall I go on?
Yes, just like this.
Well, now, in part 2 of the tripos — oh, I should perhaps say a word or two about the part 2 class of that year, which was run mainly then by Blackett. Originally it was run by a Mr. Thirkill who was a very famous person, of whom you might know at Clare College, but he really was like the old gentleman in the class and was much more involved in high university affairs than in physics, and essentially the class was run by Blackett and in fact Thirkill dropped out soon after I was involved there and Blackett largely ran that class. Well, I got to know Blackett very well. At the beginning there I used to be absolutely terrified of him, of course, and — well, then, that was how it went. The Cavendish class in those days was about 30 to 40 people. And I was in a very interesting year, by the way, a part 2 year which contained Feather, Braddick, Chalmers, Millington, quite a lot of people all of whom have remained in physics.
You say the Cavendish class. You mean, at that stage you had specialized in physics, therefore that became the Cavendish class.
Yes. You see, in natural sciences you did two or three subjects, part 1. Then you did a year doing nothing but a single subject. Now, this involved a big expenditure of time in the physics laboratory which was the top floor of the old Cavendish buildings as you know it now. If you remember the old building where you go in under the arch and so on — if you go straight up to the top of that building, that's where the part 2 of the tripos practical class used to be. The large part of our final honors year was spent there doing experiments. Blackett would come around and ask you what you were doing and why and how and things of this kind.
What courses, subject matter, did you take in the second year?
This was the third year, nominally the third year, for me the fourth because of my illness. Nothing but physics, but if you mean, in which branches of physics, then all branches of physics.
In a basic classical sense of electricity, magnetism —
Oh yes, everything; electricity, magnetism light, heat, dynamics, in fact, comprehensive physics. What we would call up here natural philosophy involving quite a good bit of applied mathematics as well and so on, but certainly no specialization allowed at all. The examination was extremely general in this sense, and with not a great deal of choice either. Relatively few questions you had to answer but quite long answers. Well, this came off all right. The examiner, the main Cambridge examiner that year was C.T.R. Wilson. Well, now, they had been going round the class wondering who wanted to research and so on afterwards, and I think it would be true to say that partly I didn't opt for this because, well, I was a little bit overwhelmed by the whole of the Cavendish. I think I was always under the impression I was doing a lot worse than I was, you know. I was in fact getting first classes all the time, but I always felt, I don't know, people like Feather and Braddick seemed so much cleverer than I thought I was. Perhaps that was the reason. Perhaps the other reason was that I'd met my wife and I was thinking we were going to be married sometime soon. But by and large I made no effort about this and I wasn't pressed to. But following the examination, I was pressed by my examiners to do some research, and this was in fact because — well, I was told privately that I came out top of this class, and C.T.R. Wilson therefore provided an opportunity for me to go into research with him, although I had made no efforts to get a government research grant. So that was how my research was first sponsored. I didn't have a government research grant as I imagine some of the other students did, four or five of them perhaps.
Had you thought of doing research with anyone else?
Why, I'd never thought of doing research at all, frankly, no, I don’t think I had. I'd found the honors work, I was thinking I was finding it terribly hard. But presumably so were the others. Well, anyway C.T.R. provided me with this opportunity, and as a result I went to work with him in 1926. Now, this was not in the Cavendish because C.T.R. Wilson had moved from the Cavendish to the Solar Physics Observatory, nominally, he always claimed, to get away from the radioactive contamination in the Cavendish and things of that kinds but I suspect in order to live in a quieter atmosphere. You know what sort of a man C.T.R. was. He wanted quietude and time to think and didn't want pressures, you see, and I think that was why he had his equipment out there, really. But anyway, I worked out there with him. I did some experimental work out there with him.
Since you hadn’t done that kind of work before, what kind of an orientation did you have? Did you participate for example in the normal “nursery” course in the Cavendish?
Oh yes, I went through that, but that was only a month or two, you know. It was merely where you were dumped when somebody wondered what to do with you, I think, in the Cavendish.
You say C.T.R. picked you out immediately in the sense of inviting you to be his research student.
Well, that was as a result of C.T.R. — I frankly don't quite know how it happened. I would think, my guess would be that C.T.R., I know he was the examiner. He was at the college I was at. He was a fellow of my own college. He was the examiner. I clearly did very well in this examination. It probably was noticed that I hadn't made any provision to research, had not applied for an SRC grant or DSR grant as it was then, and I think probably he just thought, look, this is a young man who should be persuaded to research, and he then put up the money. I mean, he had some sort of grant as Jacksonian Professor to employ an assistant, and I was that.
I saw the amounts in the annual budget. It came to I think 150 pounds eventually until 1931 or ‘32.
Yes. I also would have had a Cambridge graduate scholarship from my college as a result of my first class as well, so I would guess I probably had an income of 250, 300 a year, something like that, when I started to research.
The nursery course, that is the orientation to practical work for research students, came at about that time when you began for him?
Well, the nursery course you know was simply an attic in the Cavendish in which those research students who arrived in October with the intention of research in the Cavendish, my impression is they were always put there, to muck-about — while Chadwick and people wondered, where shall we put these people? There was really nothing much prepared there, you know — a piece of scintillation counting equipment or a vacuum array or something of this kind would be thrown at you. It would be suggested that you might do so and so and you did it, and perhaps somebody came and saw what you'd done once a week or something like that, but really I think it was a waiting a training place, rather than a training place, you know; it taught you how to live in the laboratory. That’s about all, I would think.
I’m interested that even though you did not work in the Cavendish proper at that stage you still went through this initial course or waiting period.
Yes, but that was probably just because C.T.R. Wilson thought it was a good idea for me to be there for a while, yes, that's right. But probably I was only there for a month or six weeks, you know.
Then when you started with him, did he throw you into something?
Well, he threw at me more or less his own old cloud track equipment, which I would think held hardly used much since about 1923. I wouldn't think so. His last papers I think were in 1923-26, somewhere in there. I see that’s near these dates — yes, they weren’t so much previous. At any rate it all looked to me extremely decrepit, you know bits of string and things of this kind. At any rate he more or less cast this at me and sort of told me vaguely how it functioned and suggested that I start taking some photographs. Well, I did with x-rays, I x-rayed photographs, things of that kind. I learned how to use that equipment under say casual instruction now and again from him, and used to introduce quite a number of modifications, of which he didn't show any signs of really approving of, but he was quite happy when they worked, you know. I did quite an amusing experiment here, looking for mobilities of radioactive recoil atoms, in which I took a lot of photographs which you may have seen in the Royal Society Proceedings, rather lovely photographs in which an atom in the gas would disintegrate and shoot at a particle, and if this happened before the expansion occurred, then this would separate into two trails of positive and negative ions. Now, if the atom which resulted from this alpha particle emission was say a positively charged atom, the expectation was that it would move somewhere along here, and if you were lucky enough for it to decay after you'd expanded the gas, then from where it came from you would know what its mobility was, how much it had moved in the field. Well, they all either looked like this, there, meaning that the thing was uncharged, or they looked like this, meaning that its mobility was the same as for a positive ion. I took lots of pictures of this kind which were published and they were really rather pretty pictures. But then really C.T.R. was always you know in a way more interested in the condensation process than he was in the use of the cloud chamber, you know, and he got me very involved in this — largely because I embarked on an experiment to try to measure the number of volts required to produce an ion pair. I thought I would like to try to do experiments in which I would put in X-rays of a known photon energy, characteristic copper or silver X-rays. As a result of sorting them by letting them go in before the expansion, like this, you could get them into positive and negative trails. And I thought I could count these droplets if I had very clean and very good technique, I could count these accurately and I'll know the photon energy and I'll know the mean volts to make an ion pair. So I embarked on this, and of course I rapidly ran into the troubles of running a clean expansion chamber, which I think very few people in the world have ever, ever, in fact, run a really clean expansion chamber. It’s a very difficult thing, because if you plot the number of ions that you get as a function of expansion ratio, say, in a gas — say you catch the negative ions at an expansion and the of about 1.25 and the positives at about 1.30 or so on, but always simultaneously there you run into a huge amount of condensation which happens spontaneously irrespective of the presence of ions. So if you want to catch all the positive ions and all the negative ones and have no background, the precision of using the thing has to be extremely high, and apart from all the preliminary considerations of having a chamber which is not contaminated with mucky things which would make clouds anyway — I mean, the contamination I'm talking about here is pure water condensation that causes this background which would ruin such an experiment as this. So I got involved in finding out really, could I separate condensation of pure water vapor from the background which is perhaps due to contaminants and things that you have there? And I did a lot of work on this, and I finally got methods which really ran very clean expansion chambers, and I found that if you adjusted the expansion ratio extremely precisely you could, in fact, count about 98 percent of the ions — the positives you always got fewer because they require a higher expansion ratio — but say you could count a certain number of negatives here, and you could get, this number was not increasing as you raised the expansion chamber and you could raise this up to about 98 percent before you ran into background. So I made a quite good determination of volts per ion doing this. I never wrote this up, by the way. By the way, you know that C.T.R. Wilson was a person who hated writing anything at all and he didn't ever encourage me to do any writing.
There was no other pressure from other sides?
That's right, no. Well, C.T.R. Wilson was really a person who did physics because he wanted to do it. He didn’t care much whether other people knew about it or not. Well, anyway, why I dwelt on this a little bit, of course, was that it was precisely the fact that I could do this that was available and brought me back into the Cavendish in association with the neutron problem, because I used to visit Feather at this time. Over the years I'd been doing these various things, he’d been doing the work on the long range alpha particles and things of that kind, but I used to visit him and Nimmo and they used to pump me a bit you know about expansion chamber technique, in which I felt I knew more than they did about the condensation, but they were much better than I was and had been in producing an automatic chambers which I'd never tried to do — all my photographs were taken at rather slow speeds because of the necessary conditions — but anyway, we interplayed a bit. And then of course there came this critical moment when I visited Feather one day and found him watching the chamber running, and he was trying to photograph nitrogen recoils due to neutrons, and Feather told me, this was the first I heard, about this controversy as to whether the radiation from beryllium under alpha particle bombardment was possibly a neutron, or was it a photon?
This would have been in January of 1932?
Yes, I think so, January or February of 1932.
Chadwick's letter went off about February 10 or something.
Yes. I wouldn't have known the month. I wouldn't have thought it was quite as early, but if you say so. Well, anyway, what happened here was that Feather told me these arguments and I understood the businesses about the relative sizes of the pulses that Chadwick had observed and so on, but there was quite a bit of a feeling in the Cavendish that maybe it might be a breakdown of angular momentum energy considerations, that these might in fact be particles recoiling from photons, as the Curie-Joliot, of course had suggested when they observed the radiation in the ionization chambers which was increased by paraffin, you remember, and they interpreted this as being protons which had been projected in a type of proton Compton effect. But of course, this, though perhaps thinkable for hydrogen recoil, began to get very bad for the nitrogen recoil considerations, because the necessary energy of photon was too high for it to be envisaged as a process which could result from say beryllium-9 plus helium-4, would it be going to C-13 plus a photon, you see how, of course, these matters weren't known then, and people did not — it’s very interesting, people did not apply mass energy relationships to nuclear formulae.. you know, all with a sound belief. It was done, but you know, it was often talked of in this awful quantity called Aston's packing fractions and things of this kinds and quite a lot of people I think weren't clear about it anyway. But it is interesting always to me how nobody seemed to me to regard it as absolutely certain that it was right to apply E=MC2— not in the sort of way that you might now imagine, when you think this is a piece of arithmetic which just written down nobody would question. It wasn't like that, you know. Well anyway, of course it began to get ridiculous, when you began to want photons here of 50 or 100 MeV of energy to produce the nitrogen recoils of the size that they seemed to be, because even if you allowed Carbon-13 to having no binding energy, you see, this didn’t make sense. But of course, when I use these words "binding energy" they themselves are confusing in this sense, because you can only have a binding energy if you've already decided what the structure of units in your nucleus are, see. And these, until the neutron and proton were there, you see your binding energy had to be talked of as if the thing was made up shall we say of three alpha particles and I don't know what the other thing would be, let's say an electron and a proton, that's right. Well, anyway, what happened here was that I had the conception which I was very excited about — I remember I left Feather, and I was thinking about this, and it struck me, of course the real way to do this thing was not by mucking about with these heavy things, but to fire these two things, to put this source near a chamber and look for electrons that would recoil from neutrons, because a neutron hitting an electron, say a neutron of some MeV which it would have to be hitting an electron would give a little electron track of a few KeV of energy, you see, a few millimetres long, whereas if it were a photon, then you'd get a track metres long. So I just went to Chadwick and said, "Look, you know, I can do this at once, if you'll let me have the source, I can take some photographs” and under these conditions I had I was promising I could count how many ions there are in these little tracks. Now, it's quite amusing — is this getting too personal?
No. In fact it’s necessary.
Well, it's quite amusing that first, of course, you might be thinking how stupid all this is, that neutrons won't interact with electrons, you see. You might have thought this just from their great penetration and things of that kind. But nobody said this, you know. I'll come back to that in a moment. But anyway, Chadwick was struck by this. He said, "Yes," and Chadwick used to — I used to take the source from him at about 5 or 6 at night, take it out to the Solar Physics Observatory, and Chadwick could then have a rest overnight, and whilst he was doing that took photographs all night. Incidentally, I should tell the story there that C.T.R. Wilson even was so excited by this that he used to stay large parts of the night and help run the chamber. By now he never touched the chamber. We were old fashioned, you know. We took all these photographs on plates and not on films and somebody had to change these plates and things of this kind, and C.T.R. more or less acted as an assistant for this work — although I'm not sure really that he didn't quite somewhat regret that we'd stopped our condensation work to do it, you see. But he had agreed to do this. Well, as you know, I went on and on, and I never got these tracks. And this was really the most trying time in the whole of my life, because you see every time I went into the Cavendish, Chadwick or somebody would be saying to me, "Well, have you got them yet?" you see. Insofar as they believed that I ought to get them, there was a bit of a worry that I didn’t. And of course I was really absolutely confident that they weren't there because my cloud chamber technique was quite good, and also I was getting nitrogen recoils which looked like great trunks of trees, you know, under these conditions, and it was not a question of seeing a little thing like this. You'd see hundreds of thousands of ions in these things, really like great thick sticks. But never a sign of a little electron track you see. Rutherford used to bully me unmercifully about this. "You just can't be doing it right." And then they used also to say, "We know they're there because we’ve seen them in the Shimitsu Chamber" — you know, the little hand thing that they turn. Well, of course, what they had seen was what you very easily could create if you wanted to, because you see if you run an expansion chamber under bad conditions, then when a fast electron track goes through a chamber, there will always be lots of little delta rays along it. Now, if your cloud chamber conditions are poor and you aren't photographing all the ions, you can easily lose the ions along this track and just leave yourself with the delta rays, and this certainly was what Chadwick and Rutherford thought they’d seen in the Shimitsu, and why the hell couldn't I find them, you see?
At any time did any of the Cavendish people come out to your laboratory?
Oh, Chadwick came out, yes, and — in fact, I don’t know if you've ever seen the photograph of the disintegration I have, which looks like a walking stick, like this, looks literally like that, because Chadwick — I showed him this one, and I don’t know if you’ve ever seen Chadwick’s book of mementoes. We all wrote something in a book for Chadwick, you know.
One of his birthdays, you mean — yes, I remember.
And I put in the photograph of this, with an account that this was the only time in my life when I'd ever seen him smile, when he saw this. He liked it. Well, anyway, I was frantic about this. Of course I used to go and see Peierls and talk to him as well. He wouldn't like me saying this now, but he never — nobody was taking an attitude "It's OK.”
Who was this you saw?
Peierls was there at that time.
Yes. I used to go to him and say, "What's happening?" But no theorist was saying to me — you see, this is what people would say nowadays — : "Why on earth are you doing this? It's obvious neutrons wouldn't interact with electrons." But in fact no one was saying that when there was no evidence that they didn’t.
How long did this go on?
I would think that I had a fortnight or three weeks of misery, of being told that I must be mucking this up terribly, before we began really to se the point and say, “look, it must just be that neutrons don't interact with electrons." And the more you thought about it, the more you began to see why, you see, because you began to realize that you wouldn't have this huge penetration that the neutrons had if they were losing energy by a lot of electron dissipation in their transit through materials. So that really my experiment then turned not into a critical proof on the discovery of the neutron, but into an experiment to measure the neutron-electron interaction, which I tried to do. In addition to looking for these little tracks, I did a very careful study of what you might call the background condensation in a chamber, to see if this was in any way modified by the presence or absence of the source, you see, and out of this I think I decided, no, and I got a figure of something like, I published, I forget, five or ten meters was my average distance for the lower value as to what the ion pair production could be by neutrons. Well, of course we know now it would be many kilometers, of course, but that was the experiment. Now, there were two amusing stories that I'd like to tell about this because I think you will like them. One was that in the course of doing this, of course, these experiments were quite — I used to put this beryllium alpha particle, source, very strong polonium source, on the top of my chamber and photograph, and of course I was troubled quite a bit by the gamma rays, the residual gamma rays from polonium, which gave me quite a lot of these long tracks, and which then were apt to lead you possibly to going to think that you'd seen a neutron recoil — in order to know that that was not a neutron recoil, you had to be able to see every ion along the track with great certainty and know that it was all right. I'm talking as if everybody does this, but they don't, you know. Most pictures that are taken in cloud chambers are taken under conditions in which not all the ions by any means are being photographed. But anyway, in order to cut down these gamma rays, I wanted very big absorption of the gamma rays from the polonium, but also there wasn't much intensity to play with so I wanted the densest material possible, and C.T.R. Wilson brought in all his gold medals, which he’d acquired at various parts of his life, and we put these in a magnificent little pile under the source. And I remember, one day when he had a discussion with me, which I wasn't really sure whether he was serious or not, but I think not — you never could quite tell — in which he was talking about how much we would gain if we got a file and filed off all the embossed heads on these medals, which were often quite thick you see on these gold medals, but we didn't do that, of course, no. That was one quite nice story. But I think the other story that I always like a lot because it's very personal is that when one day in the Cavendish there was a colloquium, rather like the joint triple paper which you know about in the Royal Society Proceedings — Chadwick, Feather, and I, consecutive papers —
Very rapid publication of that too.
Well, Rutherford pushed these things in fast. Well, there was a sort of preview, pre-run of those three papers in the Cavendish at a colloquium, you see. I gave the third talk at this colloquium of the three papers, and while showing a slide, I described these techniques. I'd shown pictures, you know. The one little thing which did look as if it could be one of these, you know, but which I wasn't asserting was, and this picture was like this with about sort of — well, very, very extremely clean photographs you know, and I'd shown some pictures to show how a single ion could be seen with great certainty, and this thing was on the screen, and there were two spots up in the corner like this on this photograph. And as I showed it, Rutherford boomed from the front row, "And what are the two spots at the top?" I looked at these. I hadn’t noticed them and so on. I said, "Well, I think that must be contamination. They must be two that oughtn't to be there, you see." And Rutherford boomed and said, "Well, you'd better be a bit more careful next time."
With the cleanest cloud chamber in the world.
Well, I was extremely young and innocent and frightened of Rutherford in a way, and I took this really as a reprimand, you see. It was left like that. But I was at a dinner in Trinity once and I heard him telling this as a funny story. That was when I realized that it had been a leg pull, you see. Well, this in a way of course, this experiment I think, perhaps partly because Rutherford had been so rough with me during the period when I wasn't finding the things, that when almost immediately after the events I'm talking of now, Cockcroft and Walton split the atom, Rutherford gave me the opportunity to go in and try to get photographs of the lithium alpha particle disintegration, the hydrogen lithium two alpha particle thing. I must admit that I more or less deserted C T.R. at that point, I think. You know, all the pressure of these discoveries was on strongly then, and I’m afraid that my experiments on condensation had reached a point at which I wasn't feeling really that we were getting very much further, and well, I was subjected to — I was asked, told, I suppose by Rutherford, to go in and take these photographs if I could. And I did this, and I went in and I joined in with Cockcroft and Walton.
Did that mean transferring?
Oh no, not at all, because C.T.R.'s equipment was still very old fashioned. I'd done what I could with it, you know, but it was in no way suitable to go underneath a high voltage accelerating tube. So I went into the Cavendish and I built myself a little equipment on a very low rack which could be transportable simply on a stand. I set up a whole new cloud chamber arrangement of my own, nothing like as good of course in performance as the ones that I'd been using before.
It meant spending most of your time at the Cavendish.
Oh, all. I moved into the Cavendish wholly.
Who else was working with C.T.R. Wilson?
Only Wermel, doing the thunderstorm work, no one else.
I see, so you really left him.
Yes. Just the two of us. But you know, he only visited us for about half an hour or so a day, and most of the time he would chat to us, you know. C.T.R. Wilson was a wonderful man, you know. He had a tremendous understanding of physics. He talked of every physics problem from its absolute ground floor level. For example, I'd thought I was quite good at diffraction. I thought I understood quite a lot about diffraction when I took the tripos. But C.T.R. Wilson really had a tremendous understanding of wave optics and things like that, and he used to talk to me about light and waves and things like this. He could talk about resolving powers of optical instruments, interferometers, things like that, without any piece of paper or anything. He could make it absolutely clear to you. You know of course his manner was very slow, only one sentence every half minute or so, but on the other hand he had a tremendously clear and beautiful understanding of all these things. Just in words he could make you see h t parameters in an interferometer would affect the resolving power and dispersion and things of this kind. I learned some of this from him. But —
— when it came to the other excitement —
— I think the pressure of the others, and of course I had got to know Cockcroft over this time. I was living quite near Cockcroft, and clearly it was in a very exciting period, and I thought I could do this and I built an expansion chamber setup, pretty orthodox but very compact and small which would go under an accelerating tube and look for these photographs. Well, this was a flop for two or three months because Cockcroft and Walton's beam intensity was trivial, you know, 10 -9 or something of an amp, and we gradually began to realize this and there was nothing like enough intensity for me to get photographs. And so I embarked on building a separate accelerating tube. I tagged onto their high voltage equipment, but I built a tube more of the Oliphant type, a great long tube in which I would bring the aperture in the canal ray tube right down near the chamber. I had concentric electrodes, one inside the other, so that I could bring the ion source within about a foot of my expansion chamber Instead of having it a mile away, and well, I lived through all this tremendous period in which Walton and I used to keep climbing ladders, you know, and carrying these meter-long glass cylinders up on our shoulders and sticking them up and thumbing plasticene for hours to make vaccu, and every now and then you know the bottom filament in that huge rectifier would burn out, and we'd have to take all that down and spend two or three days out gassing it. But I lived through all this, and Walton and I -well, there were three of us, you know, who did all the essential work of keeping that going, really, Walton, Birtwhistle, the technician there, and I, and really we did it, you know, because Cockcroft by now was getting very involved in work at St. John's College and wasn’t in so very much.
What time period is this?
This is now getting on, this is summer of ‘32 to end of ‘32 that I'm talking about now, I expect, yes. Well, as you know, we took lots of photographs under these tubes, and several processes, the alpha particle, the lithium, boron and beryllium, all sorts of elements like this, and then of course there was this second very exciting period when we got our first traces of deuterium from the states. I was given — if you remember the time when, there was a critical period, you know, when people were bombarding things with deuterons, and protons were observed and neutrons were observed, and the basic assumption that was being made, largely I think in Berkeley, was it…was that what was happening was, the deuteron was splitting up in the field of the nucleus. And thereby giving a neutron and a proton. But of course things didn't fit. I mean, the energies were wrong, and this led to a calculation of the mass for the neutron which was wrong and so on. And it all looked wrong. Well, as you know, Oliphant had been stimulated by Rutherford to build a Cockcroft-Walton apparatus with much lower energy than Cockcroft's but with Oliphant's very great technique in ion sources and beams, to have a much bigger beam intensity. And Oliphant of course built a very much better equipment than Cockcroft and Walto, albeit only perhaps 50, 100, whatever it was, Kev. And Oliphant was doing a lot of experiments of this kind, and he started investigating this thing and as you know they got this conception that perhaps what was happening was a branch reaction with protons and tritium on the one side and helium three and a neutron on the other. And that is was therefore wrong to be trying to associate these two. Well, Oliphant gave an account of this the other day at the Royal Society, one with which really I wouldn't wholly agree. Oliphant described how Rutherford rang him up one night when he was in bed, and he got to the phone and Rutherford said, "Look, I've got it., I know what the explanation is — you see, it’s making three, and this is where the neutrons come from." Now, my recollection of this isn't too clear, but I do know that Oliphant and Kempton’s measurements of the H1G3 reaction did show an extremely good proton peak, and I think a quite definite peak for the helium-3's although I’m not quite sure whether they went well over the top of this, because you begin to get background, but I think they probably did, more or less in equal numbers, two to be fair. So I would say without any doubt they did form this conception that H1H3was one of the processes, you see, but the thing I wouldn't allow at all and which Oliphant implied the other day was that the moment Rutherford though of these helium-3's, they looked and found some very short range particles here. Now, I find that terribly hard to believe, because these helium-3 particles have a range of only a very few millimetres and it would be right on top of their beam, and to be sure about such things would be very difficult. But my own feeling about this, you see, is that I'd been brought into this to try and get photographs of these events, and I got a photograph that looked like that you see, which was an H1, one side obviously and an H3the other, just the right two ranges and so on. Well, as Oliphant put it at this Royal Society thing the other day after his lecture was over, when somebody came along to where Oliphant and I and others were talking, he said, to me, "Weren’t you in this?" And Oliphant said, "Of course he was. He's the man who showed what was happening. We were only guessing, you see." But you wouldn't get that impression, nor would I make as strong a claim that. I would say that they did know this was on, and I think it was a guess that this was on, but I would believe that this I think was only seen when I built a separate little baby expansion chamber and I put the deuteron beam literally into this chamber so that it looked like this. Then you could just see these things coming out the end like this with just the right energy. But anyway, the real excitement of this, the first of these photographs, was that we had such a minute quantity of deuterium, I think it was a fraction of a cc — was it G.N. Lewis perhaps brought it?
He brought in three little ampules of it.
Yes, but I think the first one was very, very, very little. And Oliphant and Rutherford of course were using this, circulating it I imagine, in their low energy equipment, to study these disintegrations. But I was given a test tube, a test tube literally like that, with deuterium gas in it, and I was expected to get some photographs of this. So I got the whole thing running properly, you know, on the Cockcroft-Walton machine and I was taking photographs. I set this up at the top and I was taking photographs with hydrogen going in, you see, and then we turned a tap and let in deuterium. I think I got about 12 or 15 photographs out of this, one of which was sensational. An incredible piece of luck.
How long would it be after the actual event before the — how much time elapsed before you had an opportunity to study the photograph itself?
For me? Oh, I would say, well, it would depend how many I would take before I would develop. You see, I was very old fashioned. I used to take mine on the little plates. I don't know quite whether it was entirely old fashioned. It was largely because of the way I'd grown up through this and was trying to do things of very high quality, you know, and I never was in the spirit of taking a lot of photographs in a day, although I had to towards the end of course. I changed then. But in these days, I used to take them on little photographic plates, and I'd take half a dozen or a dozen or so and, that's right, I used to take 10 or 20 or so and put them on a rack and develop them. Let's say, in an hour, I’d have the photographs.
It’s almost a production.
Oh yes, and all the stories Oliphant tells about Rutherford dropping cigarette ash all over the special records and things were much more serious for me, you know, because he would insist on holding up these slides and dropping hot ash onto the gelatine and things of this sort, you see, which was quite a worry.
But all of this work, once you moved over into the Cavendish to build your setup, then you did all the developing and everything there, so you were at the Solar Physics Lab very little.
Oh, I didn't ever go back to the Solar Physics Lab once I left in ‘32, no, never. I doubt if I ever went inside the place again. No, I'm ashamed to say in a way it was a slight desertion of C.T.R. Wilson, in all this, you know. But I think he was quite happy. You know, he was essentially retired by now, I think. He used to come in very little. But in a way, there was something slightly disreputable perhaps about my leaving C.T.R. in the lurch, and yet I don’t think so. He was quite happy for me to do all this, I think.
But it was a kind of informal arrangement so that nothing had to be stated anyway. You were needed somewhere else and just went there and it was understood.
I would guess, you know, that Rutherford would have told C.T.R. you see.
Oh, that he wanted to borrow you.
I don't think Rutherford would have had the right to enforce things on C.T.R. But I'm sure that if — I don't know, who could know? I would guess perhaps Rutherford might have said to C.T.R. "Look, you know, he could take these photographs, it's important to have them taken," or something, and he might well have said., "It will also be better for him as a young man, you see, to come into the Cavendish rather than be a single individual just working alone all the time" as I was.
Was there someone at the Cavendish then to whom you would turn for leadership?
Oh no. Not by then, no.
For example, Chadwick?
Not on this no, and Cockcroft in a way, no, I would say I was a free agent. I did what I wanted. Cockcroft and I used to fight like hell as to who had the high voltage, you know. But I was living near Cockcroft at this time, playing golf with him and things like this, until 1932 when we all had to stop playing golf. Oh no, Cockcroft and I used to — he was the head of course, naturally, of the high voltage laboratory, and on the other hand sometimes I would get in at half past 8 in the morning. We only had one pump, you know. We only had one backing pump for the — see, I'd built this separate discharge tube, to have a milliamp of current instead of a minute fraction of a micro-amp you see — at least a hundred micro-amps instead of 10-8 or so, which is what Cockcroft and Walton had. And we only had one backing pump, in the normal parsimony of the Cavendish of those days, so that his tube couldn’t be on when mine was, you see. So I sometimes used to get to the lab at half past 8 in the morning and put the backing pump on my tube. Well, if I went out for an hour or something, then Cockcroft came in, he’d take the pump off my tube and put it on his, you see. And we used to fight a bit like this, but never, never wickedly so. Well, it was understood. Walton used to help me, you see, do these experiments. Walton ran the high voltage side, and — well, I was a guest in Cockcroft's laboratory, but Cockcroft was coming in so little that Walton and I ran the place really.
You were talking about the latter part of ‘32.
I think I've stretched along a bit now, because I doubt if the deuterium was coming there, was it, till ‘34 or ‘35.
No. I think it came in ‘33.
Was it? As quick as that, was it? I have stretched forward from ‘32.
I was going to suggest that it was Cockcroft's trip to the US in June of ‘33 that would have kept him away too. He went to the US in ‘33 to take a look at cyclotrons and other things. There’s an interesting letter that I've found that gives the flavor of the period — your writing to him — I imagine I wouldn't find many letters when you were right there together, but this was when he was in the US and you were describing the runs and the work.
This is me?
Yes. These are my notes so they're incomprehensible to you, but Cockcroft was away and I'm assuming by the dates it was the US, I know it would be the US, and you're sending photographs to him., and he wanted to use them for his talk in Chicago at the Century of Progress Exposition. It was a physics meeting too. You complained about the lack of proper equipment and the lack of time to get it fixed right, and then you said, I quote here, "Shut up in that lead box in a temperature outside of 85 degrees in the shade, I hand my clothes out to Walton bit by bit but have not yet reached the completely nude, although I'm hoping to benefit by the powerful flash of ultraviolet that hits my bare chest once every few minutes."
Wherever have you got that item? To me you're just telling me I wrote it. I haven’t the remotest memory of it.
It is the 10th of June, 1933, and it was the only letter I found of this type. It was in Cockcroft’s collection.
Have you any more of my letters?
That's the only thing I came across.
Terribly funny. I have no recollection... (off tape)
The reason I mention is that — I’d like to know a little bit more of what you were describing the actual physical conditions of doing the work. You say that you were shut up in a lead box.
I was perhaps exaggerating a bit. What month was this?
It was in June.
Yes, that's part of it. Well, you see, the point is that I built a — you know the old Cockcroft-Walton equipment, don't you, which had these two big tubes like this which they had standing on a lead hut like this, and then the beam came through here, and they started here and they used to put counter equipment here and so on. Of courses this was really ramshackle to a degree that nobody would ever believe, you know. And the leakage, the leak in this was so bad— it's really disgraceful to talk like this, but you know, when they went home at night, they used to stick a walking stick under here, because otherwise overnight the pressure went down so low in here that the whole of this bottom target part would fall off and be on the floor in the morning, you see. They used to stick a walking stick under here at night to stop it falling off.
To keep the target from falling off.
Yes, the target box at the end, you see, which was just plasticened on. And if you ask me why they didn't put a couple of screws through to hold that thing on anyway and plasticene round them, I really couldn't tell you, but this was what they did. And it really was fantastically bad. The current wasn't big, you know. Well, I built a tube over in the corner of the room, which was also in a little lead hut like this, but this was a similar tube with two sections. As far as I remember now, I had one big electrode which came down like that, which was carried here, and then the main one came down from the top and was here, you see, so that that was the main ion source, two concentric tubes here. The beam came out here, was picked up here, with this being at half voltage, and then I've drawn this too low, this ought to be right down here. This is across here, so that the two accelerating gaps are right on top of one another. And then you see my equipment was just here. So this was the lead chamber I was in. It was just three or four millimeters of lead to keep you away from the intense X radiation from the middle of the room where you had the big rectifier column, you see. There was quite a lot of X-rays in the room, you see. So it was just X-ray protection. Then I had this little rack thing that I built in here to carry my expansion chamber and everything, and then a big transformer which I had out here. C.T.R. used to have a great bank of condensers, you know, which was charged up with a huge Wimshurst Machine. It’s really almost unbelievable now to think of it. Well, in the Cavendish, by the time I got to the Cavendish, I had a nice little transformer here, which gave me a flash for the illumination, and so that's the lead box, and the flash of ultra-violet I talk about is from my lamp which is illuminating the chamber.
How big? You were in there, then.
I was sitting on the floor working the chamber, yes, and Walton was standing over at the side running the beam and giving me a shot whenever I asked for it, you see. I have a photograph of myself doing this at home.
I'd love to see that. It would make that letter come alive for me. I notice that in 1933s I guess it was in the autumn, you'd become a demonstrator in the Cavendish. This was your first official position, I guess. It shows up in the records. But apparently, this transfer of your operation to the Cavendish had occurred because you had developed the chamber to the point where the timing was perfect.
Well, I think it just happened, because I had the equipment which was capable of photographing single, of obtaining counts of ions precisely and of running a very clean chamber., and because of the possibility, which everybody felt for, that this might be an awfully good way to know that it's a neutron and not a photon, you see, which had Chadwick agreeing for me to have the source. And it was as a result of trying to do that, I think, which dissociated me from condensation studies, which I'd been doing largely with C.T.R. You see, in order to find these clean working conditions and know what background in chambers was about and everything, I was often having to study the condensation phenomenon in the absence of ionization, you see, and it was as result of that that I had this technique. By the way, this is a generality which is of historical importance, here. It's a generality, and that is, a great factor in Rutherford's successful running of the Cavendish, you know, was that when he saw the clouds breaking, everybody was pulled into it, you know. He was a great general in that sense, because if Rutherford got an idea that something was going to work or that something was possible, all the resources were thrown into that gap. It was like an Army broaching the barriers, if you see what I mean, so that I'm not wanting to say I was an important factor in this, but I'm saying that when things like the neutron or the artificial disintegration came along, all resources, however trivial, would be pulled in, and I was one of these things that were pulled in, I would say. That's how it happened. That's what took me into the Cavendish, as distinct from remaining working with C.T.R. It was just the fact that this was Rutherford's behavior, you know.
At the same time, there was just no other detection equipment available that could compare with what you had developed.
Wells you make me sound very self-flattering, saying that, but I think broadly it was true. I think perhaps Brode in America was taking cosmic ray pictures of the same sort of quality, but I don't know quite that he was taking them under conditions where he would have claimed very high accuracy of ion counting and things like this. But you see, under the conditions in which Feather was taking his, we must be fair about this, that he was trying to photograph every 20 seconds or something like that, you know, and you can't run an expansion chamber under these good conditions at that sort of rate. You've got to go through elaborate good cleaning processes and so on. I mean, their working conditions — in order to get respectable trails of alpha particles, you know, there's a quarter of a million ions along an alpha particle track. Well, if you lose nine out of ten of those, you can still make a great fat track. In other words, almost anything's good enough to take photographs of alpha particles. But if you're really wanting to photograph the sort of electrons at minimum ionizations at low pressure, you see, at normal pressure and not where you've boosted the pressure up or anything of this kind, then you see it’s quite a different matter. So really, the two techniques — I mean, Feather's was good for doing that sort of thing, mine was good for doing the other sort of thing. Neither would have done the others.
Did Blackett and Occhialini consult with you at all when they were trying to develop their technique?
Theirs was a counter-operated chamber of course, and there again they're not really concerned with ion counting so much as, again they’d be quite happy to see the tracks and know there is a track there. They weren't involved much in wanting to know the structure of a track. The track was a unit to them when they were investigating things like showers and this sort of thing. Again, they would also be working above an atmosphere, some atmosphere, perhaps of pressure, which allows the much greater ionization, you see, and much fatter, much more dense tracks this way.
I'm trying to determine if you developed a research group. I noticed that in addition to working with Walton you published a paper with Gilbert.
Yes, well, this was toward the later years before the war. We went on doing these things. Yes, I suppose — I don't quite remember what seniority Gilbert was at that time. Shall we say, he was younger than I am in a sense. He was brought in to help me with this, yes.
Your first paper with him is 1935. Then there's another ‘36. But once you moved over, you took the position of demonstrator officially. Did this mean you had additional duties that you were responsible for?
Well, I wouldn't think so. I was probably always doing some demonstrating in the Cavendish, you know.
Demonstrating for the undergraduates, you mean?
No, demonstrating to the honors class. In fact, now you're reminding me, it might even have been that when I was with C.T.R. in the initial period, that I was earning a 1ittle money by demonstrating in the honors class. I think I was. I think I went in to help Blackett demonstrate in the honors class of the Cavendish Laboratory in the very year after I took the tripos. I think I did, now you're reminding me, yes, because I know that I used to spend a lot of time with Blackett in the long vacations. The tradition in those days was that the honors examination every year was, had to have experiments, new experiments, original experiments, you see, things the students had never seen and Blackett and I used to spend quite a part of the long vacation inventing these, little wee bits of research. Like the first year deuterium was available at all in the Cavendish, we made up minute discharge tubes. We made the students in the practical exam measure the separation between H alpha and D alpha for example, and so that I think it would well be — I always had that other connection that was taking me into the Cavendish, yes, even in the days when I was working right at the beginning out at the Observatory, before ‘32.
1935 you became lecturer.
Then I became lecturer. Of course, I'd been made a college fellow, you know, somewhere along this route as well, which was providing me with half of my income, of course. I was made a fellow of Sidney, you see, of my college.
As to degrees, the research fellowship was something that just would lead into the demonstratorship and the lectureship and so forth?
Yes. I didn't do any more. In fact, the time when I would normally have been writing my PhD thesis and things of this kind, there was so much to do that nobody would have tolerated my stopping work to do it, you know. Anyway it was a slightly high hat attitude I think in some places in the Cavendish. Quite a lot of people— Rutherford sometimes used to regard the Ph.D. as something you had to take if you were going to go away, for you would need it, you see what I mean. But if you're staying, why bother about it? There was a little bit of that attitude about it sometimes, I think and certainly there was in my case, yes.
When was it clear to you and to others that you would not be going away, that you were part of the regular crew?
That's hard to say. I suppose when I was made a college fellow, and I wouldn't quite remember when that was. I'd had a thing that — I was given a Stokes studentship which was a rather more wealthy university Studentship at one stage, and I was at Pembrook for a very short period of about a year, but very rapidly after that I was invited back to my own college as an official fellow, as distinct from a research fellow, and so then I was regarding myself as stable there. Of course I was always lecturing at the Cavendish also you know, from a fairly early time. I did Alex Woods' lectures to the ordinary class quite soon — I don't remember, how soon, but not many years, perhaps only one or two years after I took the tripos. I was given the odd course of lectures to do.
Did you ever lecture on your own work, or was it more the standard lectures? By your own work, I mean detection techniques.
No. never. Of course, as I told you in regard to the tripos, the courses were always not of a research character, you know. The courses were of great generality. Most of the lecturing I did was to first year on all sorts of basic dynamics, elementary relativity, things of this kind. But in later years I did lots of lecturing in light. As a result of what I'd learned from C.T.R. Wilson, I was able to give what I thought were rather more original light lectures than you'd be likely to read, and I did a certain amount of lecturing on heat and thermodynamics and things of this kind. But of course, you know, what happened to me largely after this was — of course you know that the Cavendish collected the money to have a proper HT set, under the Austin foundation.
Do you know anything about the origins of the Austin gift, of who handled it?
— I wouldn't know what the story this is. I wouldn't really know this. I should think Chadwick or Blackett or someone would know this better. Our picture always was, you know, that Austin was told to make a good donation to the Cavendish. I don't know how the peerages and things go, but we always sort of imagined it was something like this. But of course, as soon as that money was available, Oliphant then was still with us for a while, but then Oliphant went. We got the first million volt set working in the HT lab at Cambridge. Then Oliphant went to Birmingham, of course. My last year or so at Cambridge, from when Oliphant went to Birmingham, and I wouldn’t know the date precisely but I —
— he left in ‘37, before Rutherford's death.
Wasn’t he away for more than a few months before Rutherford’s death, surely?
Yes. Exactly how many months I don't know but it was the same year.
Really? I'm surprised to hear that, because I would have thought a year at least.
Let's say ‘37, it could have been ‘36.
After Oliphant went I know that Rutherford put me in charge of the high voltage laboratory, and I was running that then, because I remember very well...yes, I'm right about that. Rutherford used to come across and sit and look at the pictures I'd taken during the day, you know, and that I think was, he was doing that very regularly after Oliphant went, I think. You see, Oliphant in a way was by nature of almost a son to Rutherford, I always think. They both came from the other side of the world and so on, and Oliphant — used to spend all his holidays with Rutherford and everything, and in a way it was almost an adoption, I would have thought. And — but after Oliphant went away, you see, Rutherford — well, he was getting on by then. He used to come and sit on a stool by the side of my bench, and we would look at the pictures I'd taken during the day, and he would always be making suggestions as to the interpretation of these pictures, you know — often very wild and exciting suggestions about what he would see on the pictures. These suggestions were nearly always wrong, you see, because he would see something which was due to some effect of condensation or something like this, and he would try to interpret this, and I would nearly always have to destroy these ideas by pointing out how they were accounted for by condensation phenomena. There's a rather improper story about that. Shall I tell it? That is, Rutherford, one day he saw something on a photograph which he thought was tremendously exciting, you see, and again I sort of killed this suggestion by explaining how it actually arose in the condensation thing, and he said, "You know, you remind me of the man who went to a solicitor and wanted to take out an injunction against the next door neighbors and when pressed as to why, the reason was that every morning when this man went to work, someone had urinated on the wall of his house the name of the first man’s daughter, you see. So the solicitor said to him, “Well yes, I can believe that that's very annoying, but why do you assume that it's your next door neighbor? He said “Oh well, I recognize the handwriting.’” This then became a very private joke between Rutherford and me, because often in company he would make this crack…"Ah, he recognizes the handwriting," you see. No one else knew why this always made him boom with laughter in relation to something I might say about a cloud track photograph or something like that, but this was the event, yes.
During this period you were in charge of the high voltage sets, and also what was the relationship of your work to the cyclotron that was developing?
None. Lewis ran the cyclotron.
Lewis was in charge, Hurst assisted?
No. I'm sorry, now which cyclotron are you talking of?
I'm talking about the one that was getting under way in the new Austin laboratory, the first one.
No, I would have said that that was almost entirely Lewis and others — Latham, wasn't it? Lewis, Latham, a number of people. We had very little contact with them, if any.
Even during the construction stage?
Not with the cyclotron people. Lewis on the other band used to interplay a lot with us in the high voltage laboratory of course because he was the genius on all our counting equipment, all our scalers and things of this kind, which of course were very amateur then and were not commercial propositions, you see, but which one would think were really like birds' nests on racks, untidy and so on, and Lewis was about the only man who could find his way around this circuitry and put things right when it went wrong.
Prior to Rutherford's death, was there anyone in charge of the new Austin developments?
You mean in the building?
Yes, the planning, the bringing in of —
— I would think Oliphant did nearly the whole of that.
I know, but the Austin laboratory was there — so we're talking of the same thing? I’m talking of the Austin high voltage laboratory, not of the new Cavendish teaching blocks and student experimental rooms. You see — no, no, at the Cavendish at the moment, the big lecture room is now occupying the whole site and volume of where the Austin high voltage laboratory was put, which has now since been disbanded. Well, of course, there's been a vast new Cavendish since then, but I don't know to what extent Austin's money was involved in that, but not much, I shouldn't think Austin's total bequest would only have been a small fraction of what the new Cavendish cost. So I would say that the Austin wing, which I always think of as meaning the high voltage laboratory, was financed by Austin and I would think that Oliphant was almost wholly responsible for the design of that, with Cockcroft perhaps taking part, but perhaps not agreeing with much of it, because Cockcroft by now was largely involved in the Mond Laboratory work, Oliphant you know had this fantastic idea that he was going to build a complete HT set under oil, and we had two vast cylinders delivered at the Cavendish in this main hall, which were, oh, I would guess 10 feet high and sort of two meters or so across and so on, and the picture always was, we were going to have to build accelerating tubes inside that and then flood the whole thing with oil, and I believe thousands of gallons of oil were even put in the tanks underneath this building. Well, neither Cockcroft nor I had any faith in this at all. We found it bad enough finding leaks in air — and the picture of having to find leaks, having run away a few thousand gallons of oil, and having to mop it all down first and things of that kind — Oliphant always used to counter all this by just saying, "You're defeatist, we aren't going to have any leaks," you see, but I don't think Cockcroft or any of us ever thought we'd have a system without any leaks. Our own experience didn't look like this. So as soon as Oliphant went to Birmingham, we all rapidly dropped all of this like a hot cake. By then Rutherford died. Bragg came. We wanted to go a bit above a million volts, and I then negotiated the purchase of the two million volt set, or 1.6 or so million volt set, which was put in the main-hall of this room. So this Austin wing was built as a high voltage laboratory. It was built as a huge hall, with two sort of concrete cells, one at each end, and the idea was big equipment would be in the middle. two or three million volts, which would then feed accelerating tubes which stood one at each end, and the beams then would come into these research rooms underneath. That was the original plan. But we started without any of that, and just by putting a million volts and the tube on the top of one of these ends. So that was the first million volt affair we ran, in which we were barely using the main hall at all. The main hall then for a considerable period was occupied by these great cylinders of Oliphant's and the preparation which never came, and as I say, when he went we got rid of this and we put a two million volt set here and tried to feed a two million volt tube there, but it was never very, very successful. We were happy up to 1-1/2, one and a half, or a bit over that, but really running two million volts bare in air is a nasty job.
How did the cyclotron come into that same laboratory? That was the intention to put the cyclotron into it. This was a continuing theme that apparently Rutherford resisted.
Yes, you shame me, because I really don't think I can tell you much about the cyclotron at all, because, it sounds bad, you know, but frankly I wasn't much interested in it. We were terribly busy in these days. We did nothing but work, you know, in these years we’re talking about now. Prior to this we used to do other things, but during these critical years we’re talking about, we more or less did nothing but work, you know.
A division of labor at this point.
Well, now, on the other hand, there would be people who could tell you fully about the cyclotron, people like Lewis, for example. But I doubt if Oliphant either could tell you much about it.
He was gone at the time. Cockcroft did.
Well, remember, you see, I wasn’t there long after Oliphant, because the moment the war came in ‘39 I was away to government work, you see. [Interruption]
Could we get back to this for a few minutes before you go?
All right. Before you rush too hard, look, I missed my other appointment, so I'll go on till 5 o'clock if that helps you.
I think there will still be a rush and we'll probably have to talk another time if you're willing. But we were just at the point of sort of covering a whole lot of ground about the transition, up until the time you went into the war work. One issue, earlier, is Chadwick's leaving — he left in 1935. That must have come as a surprise to some people, or did you see that in the works?
Well, I was always perhaps not in this sort of thing very much at the Cavendish. In fact, I think a lot of us were. People at the Cavendish I think we’re very, very much less politically minded. I think we tended, you know, to be a pretty innocent sort of crowd, in this sense, and I think there was really very little of the sort of maneuvering and lobbying or anything of this kind — perhaps it's just that I wasn't in the circles that did it. But I know very little about that. I know, of course, that after Rutherford died, those of us who were very close to one another, like, you know, Bertram and so on, we all had very strong views as to who would become acceptable Cavendish professors, and we were pumped on this by people like R.H. Fowler and so on, but really, I think none of us had much. I certainly had very little knowledge about the processes by which these choices were made. Of course, it was a bit of a blow to us when Chadwick went. I just did hear vague rumblings, you know, some people sort of saying that Chadwick was perhaps wanting to, you know, break away from parental discipline of Rutherford and things of this kind, but I would know nothing of this. I'm not a person who would know about this, and Chadwick, I would think, would almost certainly be very forthcoming about it.
It was clear that the first thing he did was build a cyclotron in Liverpool and get those kinds of things started which were rather difficult.
Yes. To some extent, you know, Chadwick was of course rather over-awed, not over-awed, he was over-shadowed by Rutherford all the time. See, there is no doubt at all that although Rutherford had the neutron, in the sense of the ten years or whatever it was earlier when he predicted the properties and everything, but the neutron discovery was Chadwick, you know. There's no question about this. On the other hand, of course, Rutherford was there as the great booming person who had no use for any of these new-angled ideas. For Rutherford the conservation of energy and momentum were two things which nobody was going to persuade him didn't apply under all circumstances, you see. So that really, to Rutherford, I think — he in a way was going around and talking like this, but I think we all of us knew that this was Chadwick who had done this. I think Chadwick did this but — to what extent, of course, it was under — Chadwick did it partly because had been brought up all these years under this attitude of Rutherford's enormous success, of course, in what was very often just applying Newtonian mechanics. And the conservation of momentum, to Rutherford was really a thing that you were not allowed to muck about with, you see. Any conception, as some people were tending to suggest, that perhaps you know, there were still photons and that momentum wasn't conserved in these processes — people were saying things like this, but clearly Rutherford just knew in his bones that this wasn't so, you see. This wasn't the basis on which anything he knew happened. So that would be my picture of this. But I don't quite know why Oliphant went. That surprises me a little bit.
Well, he explained to me. They asked him. If they had not asked him, it would not have entered his head, he said, and he was somewhat encouraged to take it by various factors. Getting back to the effect of Rutherford's death, who would have been likely successors in the view of you and other people?
If I can say that without offense to anyone now, I think one perhaps can — shall I tell you that in the high voltage lab, of which I had charge at this time, Fowler used to visit us and pump us to — the sort of question you're saying now, though not quite as objectively as that, but it was obvious what these conversations meant. Fowler, by the way, tried a little bit to fill the role after Rutherford's death of being the father and calling on us and asking us what we'd done during the day a little bit, you know. Of course it wasn't like Rutherford, because I don't think Fowler really knew much about the processes we were working on, on the resonance capture and things of that kind by then, and I don't think Fowler really knew much about this. But on the other hand, it was a nice thing that he called and chatted to us. But I've always felt that we must have been all carrying on this conversation in far too polite and far too an oblique a manner, because we were all under the impression that we had made our views very clear to Fowler, you see, which I think largely were — I think we all were hoping it would be Chadwick, you know, although we all could quite feel that it quite sensibly could be either Cockcroft or Blackett, any of these three were acceptable. But then any name beyond this — we would regard as perhaps a pity. Well, we thought we'd made this very clear, and the strange thing was that on the Saturday morning — oh, we had made a plan in the Cavendish that in order to let everybody know if the news came through when everybody wasn't about…that we would fire one spark on the HT set, one million volt spark, we would fire to the wall, if it was Chadwick, two if it was Blackett, three if it was Cockcroft. I think that was the order, you see. So that everybody would hear this and know it. And there was also, if I may make the scurrilous remark, there was the arrangement that if they heard an almighty crash, which meant that the set had been pulled down in ruins, this would mean that it was either Bragg or Appleton. Well, actually, on the Saturday morning when this election happened, Fowler called in and said, "I just wanted to call you to tell you that the election has been made and it is one of which you will all happily approve," you see, and then he went away, and we all spent the next week wondering how we'd failed so lamentably — or how Fowler could so lamentably have misunderstood what we'd all been implying all the time, you see. So how this happened, I don't know. But perhaps what Fowler was saying was, it was an election of which we all ought to approve. Which was saying something different. And as you know, Bragg came to the Cavendish, and Bragg is such a charming person that however much you didn't like this, nobody could remain cross with Bragg for long, of course. He did a little bit perhaps irritate us by, at the first Cavendish dinner I think after he came, he told us that the Cavendish had been for far too long a sort of playground for scientists to follow their own pursuits, and that there was a different point of view, which was science in relation to the nation, you see, and that science had another role than that of seeking out pure knowledge. That was its role, but it must also think about mankind and what it can do for mankind, and that all these aspects of interplay with social affairs and business and so on were also a very important area of activity in which the Cavendish could sort of make a fresh reputation. This would have been all right if he’d done it, I think, but he didn't do it as far as I could see. He ended up doing neither. So that's really the extent of the degree to which I think I ought to be scurrilous about this. But then may I say quickly that Bragg always treated me with very great kindness. He tried to do what he could. He used to come and try to talk to us about nuclear processes. I spent many an hour trying to explain to Bragg about proton capture resonance phenomena and things of this kind, but I'd always find I'd have to do it again the next week. His heart wasn't in it at all and he didn’t have any understanding of it.
Did this affect the nuclear physics people in terms of allocation of resources within the laboratory? Getting the things you needed?
No. it didn't. Bragg in fact encouraged us to go ahead and buy the two million volt set and things of this kind. No, in no way at all. In fact, I would say, you know, that this was perhaps Bragg's failure, if there was a failure. I think it would have been better had he been more ruthless. You see, I think if he had gone there and said, "Now we're going to be the best place in the world at low temperatures or crystallography or something and everything will have to run to that," — you see, then we might have been treated brutally in nuclear physics and everything, but the lab might then have acquired a great reputation in another field. But I think what Bragg lacked, you know, was this ruthlessness of Rutherford, as I said earlier, which I think is a very fundamental thing about Rutherford, that when he saw the possibility of breaking a barrier, you know, everything was thrown in. He was very tough, was Rutherford.
It's far from an academic playground.
Oh yes. Those were my words and they're probably not fair ones to use, in what Bragg said, but what Bragg implied was — those were my words and I'm not saying they were his. What he implied was that it had been a private pursuit, rather than one for society as a whole.
Isn't that the type of criticism that Oliphant mentioned in his talk that came from DIR. directly to Rutherford in the earlier years?
Oh well, of course, yes, I think so. But on the other hand, what a mess is made as a rule when your main supporting authorities and government authorities try to force their scientists to be so conscious. It's the most utter rubbish, of course. I mean, if I could revert for a second to my picture of TER., which as I say, I have far more stories to tell which have touched this field in radar than I have in relation to nuclear physics — but really there, you see, the whole success of TER. was precisely because this gang of people literally flaunted authority with regard to any form of control, in the most tremendous ways, you know.
But the practical mission was clearly in mind so no one had to be convinced of that, but the objective and the timetable —
Well, in a sense, no — yes, that is true, but I mean what I'm also saying is, you know, I have myself sat in a room with a commander of coastal commando and we have decided what the next equipment for finding submarines should be, and we have started then in the lab to make it, and each of us then put in train — they threw ministry of aircraft production and everybody else with specifications of what they wanted. People at high level vetted these, they analyzed them, they brought them down, they wrote to the establishment offices, could we make them? We reported back we could make them and so on. Finally we got instructions back from MAP saying, "OK, carry on and make this." We'd already done it, and the coastal commander had it. In other words, we just provided them with enough material in the government administration at MIT to keep them off our toes and let them go mucking about, but all the decisions were taken at TER, between the commands and the scientists, in a way that very — the histories of radar that have been written convey nothing of this, you know. I mean, the people like Whittington and so on who've written it up, they weren't really inside the place at all. They don't really know what went on.
Have you read the American account, I guess by Blackster, of the radar lab at MIT? I'm just curious if you had, whether it captured any of this spirit?
It would be interesting to compare how the two enterprises operated.
No. I would think Watson-Watts' book is as near the truth as any of it, or even Roe's own book, that horrid little book, which is scurrilous sort of book, but there's a lot of truth in it. But I think really, it's one of the most — on my desk today, you know, I have letters from the present SRC asking us to provide them with the specification of the precise three years’ work of one of the students that we propose to take on for research at this moment. And all the course training that he's going to have, the sort of activity that he'll be indulging in month after month and so on all the way through, to assess — there's nobody up there who can assess it, you see.
Why write it in the first place?
But on the whole I think you learn as you grow older the right way to deal with all this is to give them enough to keep them busy. It's a waste of public money for them to be there, but it’s much better than having them interfering.
Just one questions a final thing. After Rutherford's deaths your main focus even prior to it was within the new Austin high tension laboratory and yet you had teaching responsibilities as well.
Oh yes. I was running the honors class then myself. When Blackett went — I should have said that perhaps — when Blackett went, I took over the honors experimental class. I was in charge of it from there on, yes. These things are all done on a very informal sort of level, you know. I mean, I don't know who told me I was taking charge of the honors lab. I don't know that Rutherford ever told me to, but I did.
This continued until the time of your physically leaving to take part in war work.
I went to Exeter. A number of us went from the Cavendish in the late summer of ‘39, in case there was going to be a war, and most of the Cavendish people went to the radar establishment. Now, all of us in the high tension lab, that's Gilbert, Bertam, Devons and I, we said to hell with this. We do electronics all day long and so on. If we're going to be doing something like this, we'll do something different. We went to RAE, of all places, and we got involved in the most ludicrous projects there, with little rockets and things like this, and we were there when war broke out. We just moved automatically and so did most of the other people, only we were nine months late joining radar because we got caught up in this RAE stuff, which really, once the war came, wasn't worth doing, you see. But we gradually got absorbed back into the radar field. I never went back to Cambridge, you know. I mean I went with my family on holiday to Farmborough to work at RAE in case there was going to be a war, and none of us ever went home again.
Then your professorship came up.
I was offered the chair here. This was more or less — I was high jacked here by Tizards I always feel, in — oh, I forget, what would it be, 40 something, something like that. I didn't come till the end of the war but I was appointed before the end of the war.
Very similar to Feather then.
Feather, I think the war was really over when he came, because he had been at the Cavendish all the while.
I mean it was an immediate postwar thing.
Yes, both of us, yes.
Well, at that point —