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In footnotes or endnotes please cite AIP interviews like this:
Interview of Thomas Cowling by David DeVorkin on 1978 March 22,
Niels Bohr Library & Archives, American Institute of Physics,
College Park, MD USA,
For multiple citations, "AIP" is the preferred abbreviation for the location.
Early life in London during World War I; developing interests in mathematics; training at University of Oxford under John Nicholson, I. O. Griffith and Edward A. Milne; contact with Sydney Chapman and research on solar magnetic field and stellar structure; position at Imperial College with Chapman; comments on stellar structure studies of James Jeans, Edward Milne, and Arthur Eddington; work on Kinetic Theory of Gases and Magnetohydrodynamics and continued work in stellar structure; work during World War II and later contact with Hannes Alfvén; later positions and move to University of Leeds; growth and progress of astronomy in Britain. Also prominently mentioned are: Victor Amazaspovich Ambartsumian, Ludwig Franz Benedikt Biermann, Walter M. Elsasser, Bertil Lindblad, Alla Genrikhova Massevitch, H. S. Ruse, Erwin Schrödinger, Andréi Borísovich Sevérnyi, H. H. Turner; Baptist Church, Royal Astronomical Society, Royal Society (Great Britain), University College of North Wales, University College of Swansea, and University of Oxford.
Dr. Cowling, could we begin by a review of your early home life, your family background, and some general biographical information that would help us better understand your career.
Well, I lived in London all my early days, on the Essex side of London. My father was a person who’d had to fight for all he had because his own father died when he was not more than about 12 or 13. His mother had brought him up with two sisters. He’d begun work as an office boy and finished up as an executive engineer in the post office. He was a person of very considerable intelligence, and I owe quite a hit to the liveliness of his thought. I could never manage to beat him at chess, even though he’d never had any lessons. My mother was trained as a school teacher at Bristol, but she had had a very sheltered existence, again in the same sort of area. The two became engaged before she went off to Bristol, and they married some two years after she finished her training. There was an obligation, if you took training at one of the training colleges, to spend a certain minimum length of time in teaching, and she did her minimum length of time and then got married. I had three brothers. We had a pretty cheerful life, the sort of thing where the different brothers take it out on each other. I was number 2. My oldest brother is dead. He has been dead nearly 15 years now. The other two are still alive in London. I went to state schools all the time, an elementary school in Walthamstow, and then the local grammar school, which was a fairly old foundation. It was founded in the early 1500s, but up to the beginning of this century, it had only been a very small school, taking in a couple of dozen boys, that sort of thing. But it was enlarged in the early days of the century, when the government moved into secondary education in a fairly big way. It was still expanding when I was there. The school was, because of the ancient foundation, known as the Sir George Monoux Grammar School. You can find that in WHO’S WHO. I went to that school during the First World War and (I was there first in 1917) teachers were called up, and the school was kept going by a handful of older men. Even while I was there, there were people being called up. And what training one got very much depended on the boy, the point being that in those days, which was rather different from the present, people who got to a school like this could expect to have to work hard, and they did.
There were examinations to go to the school?
Oh yes. You had to win what they called a scholarship — in Walthamstow there were some 20 or two dozen scholarships awarded annually to the school. One was obliged to sign a form if one had a scholarship, to say the boy would stay at the school to 15. Considering everybody has to stay until 16 these days, it’s rather a changed state of affairs. I actually stayed to 18. But there were very few staying past age 16.
Let me ask you a little bit more about your home life. Was there any particular type of book that you would read, or did you have chores around the house?
Oh yes. Particularly on Saturdays, there were things like cleaning knives, polishing brass and of course the inevitable washing up. The fact that there were four boys and no girls meant that there had to be some pressure on the boys to do more than they might otherwise do. I was an omnivorous reader, and my father used to bring home a lot of magazines, some of them quite interesting and some of them not particularly, potboilers literally, so that there was always plenty of reading available.
Do you remember any particular stories or authors?
Well, I can remember reading the whole of GULLIVER’S TRAVELS. Of course, TOM BROWN’S SCHOOL DAYS. A variety of books by Kingsley. I received as prizes books like the works of a variety of poets, in particular Tennyson and Milton — those I didn’t read with quite the same intensity as other books. I’d say that I read quite a lot of adventure stories, but equally, quite a lot of the things that they call good books, and got some benefit from them.
What did you find fascinating in your recollection of GULLIVER’S TRAVELS?
Well, it’s a little difficult to be certain, because I acquired the book personally later on, without realizing then what the depth was of certain parts of it. Particularly the third part in GULLIVER’S TRAVELS, in which Gulliver visits a place where people behaved like scientists of the Royal Society did, but in a most absurd fashion. And I was able to appreciate that only later. I should imagine that in the early reading of it, I was only concerned with the big and the small people, and as for the journey to the land of the horses, well, I lust failed to grasp the irony and the savagery of it at all. I read quite a number of Jules Verne books, and there was a journal that my father had collected as a boy, known as the BOY’S OWN PAPER, which had some rather interesting serials about the life of the French hero Roland. There were school stories by Talbot Baines Reed, a person who would be regarded in these days as far too “goody-goody.” But there was undoubtedly quite a bit of interest in it. With my parents I attended the local Baptist Church, and I was for a certain length of time a member of the church choir, as a soprano.
So this was quite young.
I was quite young. Yes. But I have been a fairly regular attender of churches all my life.
You remained a Baptist.
Yes. Same connection. It was actually at church where my mother and father first met, and so there was a strong link all around in the family, as far as that was concerned.
How did your interests in mathematics develop? Did they develop early?
Very early. I can remember going to see my grandparents, when I can’t have been more than eight or nine or something of that sort, eight, I should think, at the outside, and amusing myself writing down the powers of five. It was an ability with numbers, of course, at the start. But even at the primary school, before I went to grammar school, we were taught just a little bit of algebra and quite a bit about formulas, the use of formulas, for example, in calculating simple and compound interest.
This is while you were in primary school?
Below 11. Yes. I enjoyed just playing with figures. I don’t know that I had any more depth in mathematics than other people, but just the same, the numbers themselves tended to fascinate me.
Did you have any particular teachers that you recall from your early years that could have stimulated this interest? Where do you think it came from?
I should imagine that it probably was innate to some extent. My father never claimed to be a mathematician. Naturally, having come up the hard way and having been largely self-taught, he had some difficulty over his mathematics. But he was himself an electrical engineer in the post office, and so the tendency to combine mathematics and physical interests was probably basic, and it was stimulated in the house.
Did he want you to go on to an academic career, from your recollection?
Well, he hadn’t any very clear ideas about it. But when I went into the 6th form at the age of about 15, perhaps a little bit more than that, I remember him taking me round to see a church friend who had a post in a government department. My father had hoped that I might get into some sort of government department, though whether it would be following his own line or some other, he wasn’t sure. The question was then whether I should go on to the literary side of the 6th form, or the scientific side, and the man’s advice was, “Well, they’re going to have the same amount of teaching in mathematics for both of them, and mathematics and English are the fundamentals; if I were you I’d put him into the arts side.” So I went into the arts side, and dropped physics for a couple of years, and I mastered quite a hit of Latin, which occasionally has come in useful recently, when trying to read Copernicus.
Have you read Copernicus?
Oh, scratched at it, scratched at a little hit of Copernicus, trying to chase back the originals of bits of translations I’ve seen. In the same way I have read Newton’s PRINCIPIA. I’ve been able to understand some of the bits of the original.
This is at Walthamstow that you learnt Latin?
Yes, at the grammar school. Then after two years in the 6th form, it was decided that since I’d obviously shown that I’d got some capacity in mathematics, and I was rather a puny person, rather a weakling —
— was there some problem with your health or what?
Well, my nerves were weak, liable to let me down a bit. And I was not physically very strong right all the way through. I nearly died in the first few months of my life, and so on. But it was decided that the best or safest thing would be to make me a teacher.
Who decided that, your parents or yourself?
Well, I can’t remember. But at any rate, when I was 17, expecting to stay at school one year more till I was 18, it was decided that I should try for a university scholarship, for scholarships to Oxford and Cambridge. Those were essentially the only scholarships that were particularly valuable in those days. But at the same time, because it wasn’t anticipated that a boy from a school like mine, not a particularly distinguished one, would have any great success, as a failback I asked for a place in the King’s College, London, training school — let’s say you take a degree at the college and bind yourself to be a teacher afterwards. Well, my first effort for a Cambridge scholarship (December 1923) failed. I was told I’d come fairly close. I would have had a small exhibition if I’d put my name down to it, hut knowing that the finances were going to be difficult, I didn’t. But at a second try, at Easter 1924, I was successful in getting a scholarship to Oxford. I did it just in time, because the people at King’s College were saying, “Now, you tell us you’ll take our place, or we’ll cut you off immediately.” I received the information about the scholarship in that week.
That was a pretty close call.
This was a full scholarship?
An open scholarship to Oxford in 1924. Now, I was also expecting still to be a teacher, only with a much bigger armory as an Oxford graduate. And again, to supply the sinews of war, I received a grant from the Oxford training department which continued throughout the three years of my first degree course. When I finished that, I’d got the best record in the mathematics finals that year and picked up one or two minor distinctions on the way.
What were they?
Well, they were mathematical scholarships of the university. A junior mathematical scholarship was awarded annually. There was a scholarship and an exhibition. It was only a small prize, in fact, but in my first year I got the exhibition and in the second year the scholarship. The exhibition was pretty good going because it was open to anybody in their first two years at Oxford. Well, when I got my first degree, I received a senior scholarship which would entitle me to go on to research.
Let’s not go that far just yet. I’d like to identify the influences upon you at Oxford, your professors, the colleagues and students, how you felt about life there and the general attitude toward research as opposed to teaching.
Research wasn’t a very big thing in those days. Oxford in particular was dominated by the humanities tradition, and learning was valued rather than research as such. There were people of research distinction about, but it was the tradition of general scholarship that was the dominant thing.
Did you enter with a specific program in math?
My course was mathematics. I asked about combining physics with it, but it wasn’t regarded as a desirable thing to take more than one subject. But it was possible in one’s final year to take special subjects, specializing in certain directions. In that final year I was reading electricity as a specialty.
Oh, you’ve got to understand the state of affairs. One was not working under anyone especially. Mathematics was regarded as one of the lesser interests in the university, and one attended lectures by anyone handy. Of the people that I met, who were known outside, one was G. H. Hardy, who was a pure mathematician, and a second one was A. E. H. Lowe who wrote on elasticity. He was author of a classical book on elasticity, but he didn’t lecture on it. He lectured on almost everything else in applied mathematics, like mechanics and electricity. There was also a man of less note by the name of F. B. Pidduck, who lectured on electricity, but he was a person of peculiar interests, rather than general, and I learnt more from him afterwards. He gave the first course of lectures that I attended on atomic theory, wave mechanics, in the days when it was quite new. I think that’s about 1928. If you remember, Schrodinger was 1925. There was also a man by the name of Nicholson who lectured on quantum mechanics.
Is that the same Nicholson who was very interested in what we call Bohr theory just about the time Bohr was developing it?
Yes, that would be the man.
I see. He’s a very interesting fellow. We would like to know more about him.
Well, I didn’t know him a great deal. I think by the time that I met him, he was already beginning to deteriorate. He drank slightly more than he ought to, and a little bit later, he had a complete collapse. But I can remember one rather interesting thing. In this course on wave mechanics that I attended, he lectured with a minimum of notes. He gave the first lecture completely without notes. The second lecture, he went on in much the same sort of way. And then finally he said, “Let’s see, is that right?” He pulled a postcard out of his pocket, looked, compared with what he’d written — “That’s all right.” He was a rather remarkable person in that respect, and there’s no doubt about his capacity, but because of the weakness of the mathematics in Oxford at the time, the courses on which he lectured to mathematicians were primarily on hydrodynamics.
I see. Did he ever talk about his earlier research, the development of quantum theory?
No, he didn’t speak about that, except in so far as he used it as a foundation for what was coming. What he was trying to put across was, in fact, quantum mechanics. He was speaking to a mixed collection of physicists and mathematicians, primarily physicists, so that he had to give a definitive account in the course, leaving out the difficulties but going straight through and showing you where you got to.
Would you still have those course notes?
I should doubt it, now.
That’s an interesting coincidence. I mean, he’s a very interesting fellow in the early development of atomic spectroscopy, especially in trying to figure out what the nature of the chief nebular line is. What we call I guess the forbidden lines. He never discussed this?
No. The sort of way that things were organized at Oxford didn’t encourage you to have very close contacts with the senior members, the senior people, except those in your own college. My own tutor was a man by the name of I. O. Griffith, who’d been a really brilliant mathematician as a young man, but because of the shortage of people on the science side, he found himself doubling for the position of tutor in mathematics and in physics. In fact, the only thing that I know that he wrote in either of them was a third share in a book of photometry with Lindemann, who became Lord Cherwell, and Dobson, the meteorologist.
But Griffith, because he was always overloaded rarely kept to time when he was supposed to be seeing students, and we always used to say that his first words were certain to be, “Sorry I’m late…” He did occasionally turn up just before or even lust after the official ending of the hour when we were supposed to see him. He did his level best, but he’d got rather too much on his plate. But perhaps that was an advantage, to the extent that he laid down the sort of lines along which I must go and do my studying for a particular term, and then left me to get on with it. So I did acquire a capacity for working on my own. Incidentally, in 1926, he asked me to have a look at Schrodinger’s first paper. Well, I hadn’t got enough mathematics. I hadn’t got enough German. So I’m afraid it didn’t work. But it was rather interesting.
How were your interest developing at this time, in applied math primarily?
I was interested especially in atomic theory. That was what I could see as the thing that was likely to be a chief interest. But now when I graduated in 1927, I went along to the head of the department of teacher training at Oxford and said, “Look here, I’ve just been awarded a research scholarship, should I do a couple of years of research first and then take my teacher’s training? Or should I take the teacher’s training first and then come to a couple of years of research? He said, “Take the training first, and then you’ll have it whatever happens afterward.”
This was an officer in the training school?
Yes, the director. So the next year, ‘27-‘28, I spent just taking an ordinary course in education, the history and philosophy etc. of education, and practical training where I went to a school at Bath, to learn how to teach.
How did you like that experience?
Well, I think, it was stimulating, but I always was a little afraid of the class.
What level were you teaching at in your training?
It was secondary school teaching. Between the ages of 13 and 16, let’s say, that sort of thing.
Did you find any surprises in the way the school was run, in terms of idealistic ideas you might have had about teaching?
(Broad grin). I don’t know about that. I think that one found the youngsters were an ordinary collection. But one did find, of course inevitably, that having taken the university course, you were liable to try to talk from a far too great a height to them. Anyway, this was an interesting experience. Mr. Griffith, my tutor, said that he was sure it had done me good, because after three years of learning practically nothing hut mathematics, I needed to acquire knowledge on a broader scale.
So he agreed with this idea of a year?
He felt that it was quite a good idea to get to know these things.
Was this typical for an Oxford undergraduate to do?
Why did he think it was proper for you?
Well, it was a case of have to, virtually.
But you did have a research scholarship.
Yes. But I was officially bound to go into teaching. Now, I’ve always regarded myself, since I’ve been teaching at the university, as fulfilling the spirit of the agreement to teach, but not the letter of it. Anyway, it was a gentlemen’s agreement, as was made clear, because as a minor I couldn’t enter into binding agreement. That was the year, 1927-28, and in 1928, I started on the research.
Had you always had it in your mind that you would go back to research? Or were you considering staying in teaching? Or did that experience cause you to not want to teach?
I think that one had better keep to the historical order a little more. When I talked over with Mr. Griffith the possibility of whom I might work under, he said, “Well, we’ve lust appointed to a chair a new man, Professor E. A. Milne. He’ll be taking up residence next January, and he’ll be able to take you. Write to him and see.” I wrote to him and asked him about it, and said I was rather interested in atomic theory in particular. And Milne wrote back saying, “Well, I’m afraid my atomic theory’s gone rather rusty, and if you come work with me, it will have to be on astronomy, which is my prime interest.”
Had you heard of Milne before?
No. And so, more or less by accident, I was shuffled into the astronomical field.
You had no prior interest?
No. We had had courses in astronomy as part of the mathematics degree, hut they were shocking course, courses on positional astronomy, given by the professor of astronomy. They were so dry that after attending the first couple of lectures of a course, I gave it up.
Who was that?
H. H. Turner
It was Turner still. I didn’t realize he was there that long. OK.
Yes. He was there till just after 1930, I think.
OK. And you didn’t have any contact with him, you quit the course and that was it.
Well, while I was working under Milne, he (Milne) used to run weekly what he called an advanced class, starting about 9 o’clock in the evening I suppose it would be and going on for a couple of hours, in which problems of modern astronomy were discussed. I can remember one in particular where he spoke about the theory of the nebulae as it had been recently put forward by I. Bowen of Mt. Wilson.
I see, very interesting.
One time Turner invited us over to the observatory. Turner himself had overlapped into various other things, and in particular he’d got some seismological apparatus there, and I can remember him showing us the horizontal pendulum and so on. I remember that, as I was craning forward, I leant onto the pillar that was holding the instrument. He said, “It’s a good job that I’ve got that switched off now, or we’d have had a super earthquake.” But that was as close as I got to Turner…
I’m interested in this advanced class, but this might he getting ahead of the game. What was your impression of Mime when you first saw him, your first meeting?
Well, there wasn’t anything extraordinarily impressive about him. He was, after all, a fairly short person. He was always extremely eager, and as a consequence of that eagerness, following him in a lecture was liable to be a little awkward — you were trying to take down notes and he was producing the formulae and so forth, at an enormous rate. But there was no doubt about it, he had the activity of quicksilver. He was extremely bright, and I don’t think he’d had any significant number of research students before myself. I was the only one during the first year that he was there. And as a consequence, he hadn’t mastered the art of keeping contact with people and yet encouraging them to be original, and we tended to work, to some extent, on parallel lines. The idea was that I should be working ultimately on the theory of stellar structure, in which Milne had just become interested. But during the first term that I was doing research, he hadn’t arrived yet at Oxford. He gave me a reading list which included volumes like Eddington’s INTERNAL CONSTITUTION, and a book by Stratton and one by Dingle,  as well as books on thermodynamics, Planck, the original Planck’s “Heat Radiation”.
That was in the original German?
I can’t remember. But I managed to wade through it by this time.
So you were learning definitely — Stratton would he ASTRONOMICAL PHYSICS.
Eddington, this is all pretty much in physics and astronomical physics.
Eddington, this is all pretty much in physics and astronomical physics.
Yes. There was also Jeans’ KINETIC THEORY OF GASES. Which itself became significant, in later times.
What were your impressions of problems posed in these books, especially in Eddington, problems that had to be solved in astronomy?
Eddington unfortunately had a way of presenting things as if everything had been’ done. It wasn’t quite as true in the INTERNAL CONSTITUTION as in some others of his volumes, notably the THEORY OF RELATIVITY. There were too many loose ends in it. But I didn’t appreciate the inwardness of his work. I’m afraid I got mental indigestion before long. Well, Milne arrived. I was attending lectures that he gave in that year on the theory of stellar atmospheres, which was his masterpiece really. And the following year, he lectured on the thermodynamics in accordance with the ideas of carathrodory which is thermodynamics with an axiomatic approach. He tended to get one out of one’s depth, because of the speed and the careering as he went along. On the other hand, his lectures in the advanced class, where everybody was starting at the same level, were rather masterly ones. Introducing a new subject, it was new to him, and he presented it with all its novelty, and it went home.
In this advanced class, he chose the topics?
He chose the topics. He got people to give lectures, and in my second year, when I’d already got somewhere, I spoke about some work I’d been doing. I spoke twice that year.
You’d been working on magnetic problems?
When Milne came, his ideas in stellar structure weren’t sufficiently developed for him to want to throw me into it. And he was a close friend of (Sydney) Chapman. Chapman had introduced him to research. He spoke to Chapman and said, “Could you suggest a problem that I could throw a new research student into, and that wouldn’t take up too much of the time?” Chapman said, “Well, there’s some work that I’ve been doing on the radial limitation of the sun’s magnetic field, and I’ve seen how it can be explained, but I’d like just to have information as to what depths are characteristic of different sizes of magnetic fields.” So I had to read up a little hit about the Zeeman effect and such things as that, and then try to make the appropriate calculations. I made extremely heavy going of it. I just felt I couldn’t catch hold of the problem. When Milne was going off to Ann Arbor in June, he summoned me for the last time to give instructions, and gave me the address that he was going to.
These were the Michigan Summer Institutes?
I don’t know what it was in those days. He made a number of visits to Ann Arbor. Then he gave me the address, so I could write to him if I wanted anything explained, but he had been rather depressing to me around about that time. One thing that might have contributed to it was this: Milne gave the Bakerian Lecture of the Royal Society in 1929. He had wanted to talk about his ideas of stellar structure, but they were already proving rather controversial, and he was advised to take a more settled subject. So he hastily changed over, and gave the lecture on stellar atmospheres.
Who advised him of this?
I don’t know, but I should imagine it was a case of feeling that Eddington was very violently critical and so he just took the hint, more than anything else. Anyway, he had to preserve his Bakerian Lecture in a hurry, so when I was going down in the Easter of 1929, having had contact with him only for three months, he said, “Look, I wonder if you could do some calculations for me? I’m wanting to get calculations to show at what temperature a particular line ought to show its maximum and so forth.”
This is in 1929?
Yes. Well, he’d done crude calculations like this earlier with R. H. Fowler. But he wanted these up to date and he said, “I want calculations for so and so and so and so, a certain helium line, hydrogen, magnesium and so on, and he gave me the formula –- all I’d got to do was to calculate using that formula –- but there were statistical weights turning up. I said, “Where shall I find the statistical weights?” He said, “Oh, probably in Fowler, Fowler’s STATISTICAL MECHANICS.” And I was due to be going down and leaving Oxford in an hour or so. So there was no question of my being able to hunt up these things before I went down (to London). I found myself unable to trace the references. I made the calculations, but assuming equal statistical weights in the excited and the ground states, and of course, they illustrated the sort of pattern beautifully, but they didn’t illustrate things exactly, as Milne had hoped that they might.
Did you have access to Cecelia Payne’s work on atmospheres?
Well, I was still trying to find my feet, I didn’t know my way about.
You didn’t know the literature.
I didn’t know the literature. Anyway, Milne took it gracefully, despite his disappointment, but there may have been some relation to it that in the summer term, particularly when I was finding such difficulty in getting down to Chapman’s Zeeman effect problem, he suggested that perhaps I ought to think again of a teaching post when my research scholarship grant ran out.
How did you feel about that? When he said that?
Well, I was prepared to be guided. I hadn’t definitely made up my mind where I was going to go. I knew that things would be rather difficult in other directions. Anyway, he went off to Ann Arbor. The term lasted some ten days after that. And suddenly, instead of carrying out the calculations that Chapman had suggested, I found myself working on a parallel problem, on the actual theory of the process that Chapman was appealing to.
How do you think you made that transition? Something didn’t look right in Chapman’s work?
Well, I don’t know that it was that, or lust the general feeling of irritation, that I wanted to be able to do something. Then to my surprise I found that Chapman’s work was founded on a fallacy. I wrote to Milne immediately, and explained it. Milne wasn’t too sure about the situation, but he showed it to Rosseland who was at Ann Arbor at the time, and Rosseland seemed to think it was something reasonable. Apparently, Chapman’s work had been criticized by people like R. H. Fowler, only privately of course, because it seemed to create currents, electric currents, without there being any expenditure of work, so there seemed to be something fishy in it.
People would object to that.
But of course you, later on, worked on induced electric currents yourself.
Oh yes. Yes. That was a different thing. You see, in this particular case, effectively the currents would flow only when the atmosphere was settling down in the sun. If it was supposed to be in equilibrium, there wouldn’t be any current.
Anyway, I wrote Chapman at the same time. I proceeded to make a particular mistake in presenting it, because I suggested an alternative mechanism, and forgot to notice that there was a distinction between electrostatic and electromagnetic units, and as a consequence of my neglect, I mislaid a factor of 9 x 1020 which didn’t increase Chapman’s belief in my work. But when Milne came back, and I wrote to Chapman again, he said, “Well, Milne seems to think you’re right, and I rather rely on Milne.” So that was when I first came into contact with Chapman, in the summer of 1929.
I see. You never contacted him while he was still at Oxford, before Milne came.
He was never at Oxford before Mime came. He wasn’t in Oxford until 1946. He came along a completely different route. He graduated at Cambridge. He spent some time at Greenwich Observatory. Then he went back to Cambridge, and played kettledrums between Cambridge and Greenwich, until 1919. Then he was appointed professor at Manchester, and in 1924, appointed professor at the Imperial College, where he was until 1946.
I see. OK
Milne in fact was his successor at Manchester, before he came to Oxford.
OK, I have that straight now.
My first paper was the paper that took Chapman’s work to pieces. When I returned to Oxford in October, I remember Mime coming to me one day and producing the rough manuscript that I’d got of this paper on Chapman, and asking me if I could get it into a form where it would he suitable for publication, so that he could take it up to the Royal Astronomical Society the next day.
The next day?
The next day. I worked right through the night, and I produced it for him just before he went off to London the next day. But when I’d gone back to Oxford, he suggested that I might start the work on stellar structure that officially I was supposed to be working on. And I was working on that, up to the time when I went down from Oxford in 1930. It was on a rather artificial model of a star, hut it was made some use of by Milne, in connection with his own ideas in those days. When I went down from Oxford in 1930 I’d got to find a post somehow, and after some difficulties, I more or less was offered a post by Chapman, who by this time had satisfied himself about my capacity, and well, it’s a thing I never regretted. This was at the Imperial College. I was under him for three years.
He offered it unsolicited by you?
Well, it wasn’t quite that. I’d been in for a post elsewhere in London, and Chapman had learnt that I’d applied for this, but hadn’t applied for a post that he was offering, because I didn’t know of its existence.
I see. Milne didn’t direct you at all on this?
No. So when I’d finished my interview and been turned down at King’s College, London, the secretary of the college, whom I slightly knew, came out and said, “I’ve heard from Chapman that he was wondering why you hadn’t applied for his post.” I said, “Oh? I didn’t know about it…” He found the copy of NATURE that had the advertisement, and it was more or less the same sort of level post as the one at King’s College, and I wrote Chapman and asked him if it was too late to submit an application?
You wrote. You didn’t phone or anything like that?
No. The reply came back, “Come along on such and such a day, and bring your testimonials with you,” and I was appointed. Well, this was about the most fortunate accident of my life, I think. Anyway, during the year 1930, Milne was producing his own theory of stellar structure, which I had some doubts about, because being a person with a strong sense of the orthodox, I thought that Eddington’s orthodoxy represented the orthodox, and Milne was the heterodox.
This was Eddington’s Standard Model?
Yes. The theory as it was in the INTERNAL CONSTITUTION. There was one particular point that Milne was stressing. It amounted to a possibility of being able to get in an extra degree of freedom into the stellar models, by invoking properties of degenerate gases.
Is this the first you’d heard of degeneracy — through Milne?
Well, in its astronomical application certainly I had heard about it. It’s quite possible I’d heard about it well before 1930 in Fowler’s work.
But you didn’t consider that heresy?
Oh no. No, that I regarded as part of the orthodoxy, provided you accepted quantum mechanics.
Right. OK, good.
But it was the idea that you could hold a star together, at an immense density at the center, by itself, without anything to push the stuff together, that was the thing that caused me the difficulty. There was a discussion held at the Royal Astronomical Society in January, 1931, which was supposed to be a continuation of the argument over Milne’s theory, when it was presented in the previous November. Milne in fact presented a rather neutral account, only stressing the history of the developments. Fowler and I went out to give an account of bits where our work had impinged on Milne’s. And I had by this time discovered a disproof of Milne’s claim that you could round things off with a degenerate core, and mentioned this, instead of supporting Milne at the meeting. I said I didn’t think that it was impossible that one might be able to find a way of rounding things off, hut it was not the way that Milne had suggested.
This was a surprise to him?
It was the first, I think, he’d heard of it. And I proceeded to put it in a rather tentative, fashion at the meeting, but in a more definite form in writing to him. Well, he’d already felt a certain amount of irritation about my attempts still to hang onto his apron strings, after I’d left Oxford.
What were these attempts? You mentioned you wrote him a lot of letters.
I wrote him enormous long letters, and he found it rather difficult even to find time to reply to them.
Did you ever keep copies of these letters? Do you have any recollection where they might be?
No. No, they wouldn’t have been kept. I don’t think these were particularly important, in any case. No. They were not things that advanced anything, but letters that you write to air opinions about this and that.
Were you looking at white dwarfs at all at that time? I know you never really did, but as far as your use of degeneracy in the core, some people started looking at white dwarfs as the possible embodiment of cores of stars.
Well, I think that I was quite happy to accept white dwarfs as degenerate. Obviously, you’ve got to make quite a distinct jump from normal stars — they’re not the normal stars.
Right. Were you thinking of evolution at all at that time?
OK. So you’d give this paper at the Royal Astronomical Society?
Well, I didn’t give a paper. The paper came later on in the year.
You made this original statement to Mime. What was his reaction at the time?
Well, his reaction generally was, “I don’t know enough about pour idea” and so on. But when I’d given it in a definite form, he did blow me up, rather. And I had to appeal to Chapman, who very kindly proceeded to act as the intermediary and make things right between us. I was very grateful to Chapman. When I had received Milne’s letter in the early morning, I went in a shattered condition down to the Imperial College, and as Chapman was coming from a lecture, I said, “Could I have a word with you?” He said, “Yes.” I said, “I’ve just received this letter.” He read it and then began to laugh. I said, “I don’t really find it very funny.” He said, “When did you have it?” I told him, an hour or so before. He said, “I think I can understand why you feel like that.” But anyway, he was extremely wise about it. He reminded me of the various ways in which I’d been indebted to Milne, and said, “You know that you have perhaps transgressed the usual rules a bit. Just you remember the extent to which you’ve been indebted to him, and I’ll see if I can do anything.” Anyway, at tea before the next meeting of the Royal Astronomical Society, he called me out, and we walked around Burlington House Square and hammered things out. At any rate, we ironed out our disagreement.
How did you iron it out?
Virtually speaking, by each of us emphasizing the points of agreement, rather than the points of disagreement. It wasn’t a case of having to accept the other person’s point of view, but rather, having to accept that whether one disagreed or not, one could he, one had to be friends.
That’s interesting. So the points of disagreement were what? Were they over interpretation, mathematics?
Milne accepted that, so far as my analysis went, I was right. He was still hoping that one might be able, with the help of the relative transparency of degenerate matter, to be able to get somewhere. It was Chandrasekhar who established that that was no way out. But it was also true that there were two other people who proceeded to prove the same result as I — Hopf proceeded to, and H. N. Russell, by a very ingenious method.
Hopf and Russell?
Yes. You’ll find the papers both in the MONTHLY NOTICES, 1931.
Did Milne talk about Russell’s method at all at that time?
Milne himself was set the lob of describing Russell’s method to the Royal Astronomical Society, and I must say, he gave a very clear account. Oh yes. He’d accepted that as far as things went — without going and introducing extra assumptions — the proof that had been given was an accurate one.
Did you read Russell’s paper at that point?
Oh yes, I read Russell’s paper. I was reading all the papers that came out about that sort of thing. I’m afraid, in my endeavor to support Milne now as much as possible, I distorted a Council Note on stellar structure. The Council of the Royal Astronomical Society prepared annually notes on advances in astronomy. They had this year a note on the theory of stellar structure, and I was asked to write it. I emphasized only the work that was being done on developing Mime’s theory, and played down the extreme criticisms that Eddington had produced on it, to the extent that when it was read to Council, Eddington said, “That really ought to be rewritten.”
He said this in the —
In the Council. Yes. I had to rewrite it, putting a balance.
Do you have the original draft?
It would be very interesting. Was Eddington that powerful, that he could demand this?
I don’t know. But I think he was correct, as he said that I 1ust hadn’t mentioned his criticisms, and a fair note would have mentioned them. Even if one is going to take sides, one ought not to suppress.
Did Jeans’s work enter into this at all at the time, his liquid stars?
It did and didn’t. If you look at the accounts in “Observatory” Milne presented his ideas on stellar structure in a relatively undeveloped form in November, 1929, to the Royal Astronomical Society. He presented an account of them at Oxford about the same time. Well, when they were first presented to the Royal Astronomical Society, Jeans said, “Oh, what he’s saying is only what I’ve been saying in criticism of Eddington for such and such a length of time…” But later when he’d read it more fully and Milne had presented his ideas more clearly, it was clear that they differed completely from Jeans’s earlier concepts. Jeans now said, “There isn’t room for Milne’s theory. Either the stars are gaseous, in which case Eddington’s theory is right, or they’re liquid, in which case I’m right.”
Did he say this sort of thing at the meetings themselves?
This is what he said in the general discussion in January 1931.
‘31. How did the audience react to such barbs back and forth? With laughter or what?
It was diamond cut diamond. I think everybody was absorbed, sitting at ringside seats.
These meetings did become quite well attended, I understand, as the controversy continued.
When Milne presented his first account at Oxford, the man who was in the chair introducing him said, “You will remember that when Jeans and Eddington were throwing things at each other, quite a number of us joined the Royal Astronomical Society just to listen in to them. Now, we are carrying the thing a stage farther…” So the idea of controversy wasn’t by any means a new one…
Yes. Well, you certainly got thrown into the fray.
How did you feel about that, up against these people, interpreting their work and criticizing their work?
Well, I was a beginner, more or less, and I was more interested in finding problems that I could tackle than in ultimately dealing the orthodoxy of things, and I’m afraid that at this point, the supply of problems seems to have dried up.
Why was that, do you think? Was there an impasse in stellar structure? No one knew what the energy generation was.
Well, it was more a case of not having any idea of what to do except working out simple models, and it seemed to me that simple models had already been dealt with adequately. But while I was in rather a depression about this —
— Chapman passed over to me a set of notes of a book that he’d tried to start some years before, and had been unable to complete. His aim was simply to enable me to see the impact of kinetic theory on magnetic problems, which I was working on at the time, but it enabled one to see kinetic theory as a developed whole, instead of the collection of approximations and tricks that had been represented in Jeans’s work. And I returned it to him with considerable enthusiasm, and after thinking about it, he invited me to see if I could help to complete the book. He was not imagining at the time that it would he more than a case of doing some routine work, I mean, obtaining comparisons with experiment and so forth. But in practice, as things developed, I began to see much bigger possibilities. I actually worked on the kinetic theory of ionized gas in magnetic fields, round about that time. But I could see the difficulties caused by the overlap of the electrostatic fields of charged particles, and gave up that work for the time being.
Well, to identify that influence, this certainly started you working with him. Did that develop into the book A MATHEMATICAL THEORY OF NON-UNIFORM GASES?
Yes. I completed most of my own personal contribution to that by 1935. It might have been written a little earlier. It probably was a little earlier, because Chapman then had the book, had the incomplete version, for something like a year before we finally got down to it. And then on one long vacation, we just spent several days reading it through, after which I produced down a new version, which even then was well away from completion.
It took quite a while.
Well, during this time, you started revising your work in sunspot magnetic fields. Also in ‘35 your “Cowling Model” developed. Which would you like to talk about?
Well, it was Chapman, a hint in Chapman’s work, that set me going on the dynamo problem, and all that I could see when I started was a relatively routine piece of difficult computation, but I thought it was worth doing.
Was this in ‘33? You were still in Imperial College?
Yes. And as I got down to it, I found that I’d got a real difficulty at the neutral point of the field, and, I couldn’t see how to tackle that computation.
How the lines of force got there?
Now how the got there, but how the field was maintained at that point, because the lines of force were curving round and you’ve got a current flowing. And yet despite that, since there was no magnetic field there, you couldn’t get an electric field induced by the V X B result. And finally, after stewing around and trying to see how I could get through it, I decided that the idea was wrong, and published the theorem about the impossibility of self—maintained symmetric dynamos.
Right. I knew you were quite critical of that at first. You were talking about the effect of the induced currents, criticizing the Larmor theory.
It was the Larmor theory ultimately that I was criticizing.
Yet you had started working on the dynamo effect at that time but you hadn’t got down to it. You didn’t think that was going to work either.
I didn’t think it was going to work. No, that’s quite true. And I think, as far as dynamo theory is concerned, my work was always as the anvil rather than the hammer. Anyway, that appeared, and then, there was the question of sunspots. Now, Milne had done a little work on sunspots, and the theory that was often supported in those days was that the sunspot was dark because the material was in a process of convection and it was cooling as it rose. This seemed to me to have some difficulties, because if the material was going to be cooler when it rose, then there was always a back reaction mechanically, and so, you’d got a means of destroying the effect that you were concerned with. And at the same time, following other people’s work, and notably some work that Chandrasekhar had done. I satisfied myself that you’d got a super-adiabatic gradient, and so the material ought to rise, and be hot when it had risen, so you shouldn’t get a cold spot, but a hot spot.
Did you see this mechanically? You saw the necessity for this from a mechanical view?
It was from the mechanical point of view that I saw it. You can consult a report of the meeting at which I presented this; I presented both my first paper on stellar stability and this one at the same meeting. You’ll find a report in the OBSERVATORY MAGAZINE.
Somewhere round there.
Yes, I have that reference to magnetic fields and sunspots. 
I did at that time make a first suggestion that had to do with magnetohydrodynamics, in that I suggested that a large magnetic field could be produced by some sort of compressive process. My memory isn’t clear enough to remember now exactly what I said, but I did get a little way into magnetohydrodynamics there.
Well, now we’re getting into the stage where I made contact with L. Biermann.
Yes, that’s right.
I first heard of him at a meeting of the Royal Astronomical Society, when Eddington was asked by somebody else, probably G. C. McVittie, what he thought about a paper by L. Biermann — a paper in which Biermann claimed to have got rid of what was known as the opacity difficulty.
A problem with the absorption coefficients.
Yes. It wasn’t really a difficulty about opacity, it arose because people didn’t realize that the atmosphere was largely hydrogen. Eddington then said, “Well, he’s got rid of half of it by changing the wrong value for a particular constant, and the other half he’s got rid of because he’s dealing with a point source model —”
Eddington was saying this of Biermann?
Yes. But then, another paper appeared from Biermann, which was the first to apply ideas of turbulence in the core of a star. Now, accidents happen. It’s purely accidental that I read this paper when, about this time, after three years under Chapman, I moved off to a post at Swansea.
Parenthetically, why did you move to Swansea.
Had to. The rules were rather strict in those days. A person’s first appointment was a three year or at most a four year appointment, and if there was a vacancy then, he could be appointed to the higher grade. If there was not — out.
Then you applied for the Swansea position.
I applied for the Swansea position and got that, after three years under Chapman. Now, while I was at Swansea, there was another prize turning up at Oxford, a postgraduate prize, and I decided to try for that, a Gold Medal that was awarded every now and then. And having read papers by McCrea on the effect of mixing in the chromospheres, and also Biermann’s paper on convection in the core, I chose as my subject Convection in Stars. And I was able to develop Biermann’s ideas to some extent, and this began to tie up with work that I’d begun to do on theory of stellar structure. It was clear to me, first of all, that if you had too great a concentration of the sources towards the center, there would be a convectively unstable equilibrium.
This is a point source model?
Well, virtually, but in fact, I had considered energy generation that was dependent on a power of the temperature and showed that you couldn’t get above a certain power of temperature without getting convectively unstable conditions at the center. Then, I didn’t develop those ideas beyond having found the limit, because what I was now interested in was the theory of stability. There was a paper that was produced by Rosseland about 1930, in the ASTROPHYSICIA NORVEGICA in which he discussed the problem of stability. If I’d realized that Eddington had discussed essentially that problem, and drawn much of the teeth out of it, in the INTERNAL CONSTITUTION, I wouldn’t have gone any further. But luckily I didn’t realize it because I was able to establish a criterion based on Rosseland, but which could have been derived much more simply by Eddington’s methods, for the stability, and to show that a star must be stable in the sense of neither blowing up nor being subject to increasing oscillations, whenever you haven’t got convection in the core. That’s Paper No. 1.  Well, that left open the question of what happens if you’ve got a higher power of the temperature? Incidentally, that first paper I presented to the Royal Astronomical Society without knowing of some work that had been done by a research student under Eddington. And I saw his paper during tea at the Royal Astronomical Society when I was to give an account of this paper.
Yes. And I had to tell the secretary that I was withdrawing the paper and wouldn’t give an account of it. I had to rewrite it, in a much better form, as it turned out, by the time I’d finished. But it was rather shattering.
To me, yes.
How did the secretary take it?
Well, he’d got just about enough papers.
So, it didn’t bother him?
It didn’t bother him too much. I was only going to be allowed ten minutes or so.
Oh, I see. OK. You certainly at that point intended to modify your paper.
Yes. Oh yes, I did modify it, and produced it again in a much better form, later. Anyway, I said there was this prize at Oxford I was going to enter for. And having gotten interested in convection from the outside, I went straight into convection on the inside, and produced an essay under great strain, lust in time, about the last day, and won the Gold Medal.
You did win the Gold Medal.
I did win the Gold Medal. Yes. And then published my second paper later on, and I realized that in order to get to the problem of stability, which was still the one that was worrying me, in the center of the star, I’d got to study model with a convectively unstable center. And for that, I just took the simplest possible sort of assumptions that one could, placing all the sources of energy in the convective center, and saying, “This will work, provided one’s got a very rapid variation of energy generation with temperature, such Atkinson suggested in earlier work,” and this was the Cowling Model, as it was called by Chandrasekhar particularly.
He was the one who first identified it as such?
He called it such. Yes. This was presented in an appendix to the main paper on stellar stability. But when I’d finished, I was stressing the fact that whereas Jeans, whose ideas had introduced me to the ideas of stellar stability, insisted, that there were two sorts of instability, and there’s hardly any room for any stars in between unless you had a good liquid core or something of that sort, in fact he instability was likely to be completely unimportant, except under extreme conditions. So I got that, and also the Cowling Model, into one and the same paper.  I felt pleased about the first aspect of it. The other one proved quite important. Biermann took it over to a certain extent, just to see what consequences you got and so on.
People were very worried at that time about the degree of mixing in a star. Now, when you came out with a model like this, did people talk about mixing?
No. You’re a little too early as yet. They did say something about mixing, but it was only a little later that the ideas of mixing or non-mixing in connection with the evolution of stars became important.
Did you ever address that problem yourself?
Well, as a matter of fact, yes, but that was not until very considerably later.
It was quite clear from earlier work that if you’d got convection currents which were moderately effective, mixing would he reasonably perfect, and at that time, one was hoping that stars would remain homogeneous. And in any case, since one didn’t know the process by which energy was generated, it was perfectly possible to say it was generated by a process which destroyed matter completely.
Yes. And therefore you wouldn’t need to have any change in the composition during evolution.
Were you aware of Opik’s very early work on stratified models at that time?
What about Stromgren’s work starting about 1930, especially with his work on H-R Diagram by ‘33? Did these concern you at all?
They didn’t concern me particularly. I was cognizant of them, but it seemed to me that it was distinctly speculative. In fact, I think I was not altogether wrong, in that the H-R Diagrams that one’s discovered since have been rather different in their origin, from those that Stromgren was concerned with.
In what way? I’m interested in your point of view on that.
Well, Stromgren was producing an H-R Diagram in which he’d got a variable percentage of hydrogen.
That was in his ‘33 paper where he had lines of constant composition. All right.
Yes. And he was trying to explain the different H-R diagrams for globular clusters or galactic clusters, it would have been, in terms of differences in composition. But in fact, it wasn’t a particularly good fit.
No, not at that time. The important thing was that you were not concerned.
I was not concerned myself, no. In any case, I concentrated in those days on the mass/luminosity relation, almost to the exclusion of other things.
Because, there was the great big difference between Eddington, Jeans, Milne?
Well, how did you concentrate on it?
Chiefly by disregarding other things, I’m afraid.
In a way, Eddington turned out to be physically pretty close to the mark.
As far as he went, yes. They said, as compared with Jeans, Eddington, though officially an astronomer, was closer to physics than Jeans, the physicist, was.
That’s interesting. Did you ever experience this directly, let’s say, in his discussions at the Royal Society, or whenever you might have met him?
When Chandrasekhar’s book on stellar structure came out, I had the thing to review, and I noticed that he’d got essentially two chapters trying to discuss the Trumpler stars, which didn’t seem to fit onto the mass/luminosity diagram. And I asked Eddington how he dealt with these things. He said, “Well, I don’t really believe in the observational data and the parallaxes being used. They’re all spectroscopic parallaxes, and I just don’t believe they’re right.” And in fact, he was right.
How far off were they?
Well, if you look at Chandrasekhar’s book, it shows a diagram of that. I can produce it later on if you’d like.
That’s interesting. So he had a pretty good intuition on those things.
Oh, he had a very good intuition. It’s only towards the end of the thirties, when he became interested in what he called “fundamental theory,” where the number 137 turns up, that he began to get his head so far in the clouds that you couldn’t follow him.
Yes, I’m somewhat aware of that. OK, well, concentrating then, on your work on stellar structure, beyond the Cowling Model work, in what directions did you continue to work, or did you?
I didn’t go a great deal beyond that. I did a little more on stellar stability. But for the main, I’d finished what I could do, then.
In 1941, not to jump too far ahead hut lust finish with stellar structure for now, you did work on non-radial oscillations of polytropic stars.
I’m just curious; about then, you were also interested in the problem of tidal distortion in binary stars. 
Were you interested in it from the standpoint of understanding better the apsidal motion tests or something?
Well, there were two distinct papers that I published around about that time. One was concerned with the apsidal motion question. There, I was following up some work that Z. Kopal had done, which I was not satisfied with. It seemed to me unsatisfactory mathematically, and I thought I’d try to clear up the mathematics, but when it came to it, it became a good deal more than that. It established that you’d got effectively that the tidal distortion was going to be at any moment nearly the equilibrium tidal distortion. And it implied a rate of apsidal rotation that was a good deal less than anything that Kopal had had, and which wasn’t far from what scanty data were available at that time.
What about your agreement or disagreement with Russell’s original exposition of the apsidal motion test? Had you read his papers to start?
No. I’m afraid not.
It was lust in Kopal’s direction.
Well, it’s quite possible that Russell’s stuff filtered through. But you see, in the early days, one would have said, let’s work it out assuming that we’ve got a star that’s a liquid star, and see what apsidal motion you get in that case.
Yes, you’re pretty much forced to that.
Well, the other paper was the one on non-radial oscillations, which has proved a fairly popular topic in. recent work.  That started because of interest in instability. I felt it ought to be possible to obtain a criterion for the instability, convective instability, directly. You always are concerned with vibrations in such cases, and the vibrations passing over the limit of stability, and I couldn’t make any progress except in a very general sense. I could see, more or less, where the instability would rise, but I couldn’t nail it down. So I got to some extremely awkward equations, and didn’t know quite how to bring out their meaning. Wartime was now on us.
World War II, of course.
Yes. I was an air raid warden locally in Manchester where I was now living. And we had to spend quite a bit of time on volunteer duty.
You were a civilian through World War II?
You had to spend quite a bit of time waiting for a call at a small blockhouse that they’d got for us. So I took some log tables and so on, and proceeded to do a computation on the equations. I don’t think I’d have had enough courage, if I hadn’t had all this unwanted time when you do much else. But anyway, the paper was finally published, and I didn’t regard it as anything particularly wonderful, hut other people thought more of it than I did.
Well, those are very important papers. People are still trying to understand Cepheids and related problems.
To Cal Tech and then to Princeton.
Is this partially from your interest in stability?
No. I did do a little work on rotation in stars, round about this time. I don’t regard that as particularly important, hut some people have spent time trying to show that I was wrong since then.
This was on the effect of rotation on mixing?
On stability generally. Yes.
Who brought you to Princeton and Cal Tech? How did you arrange this?
I had an invitation in 1949, I think, when I’d only just come to Leeds, and I didn’t feel able to accept it then, hut I accepted it in 1950, on the advice of the vice chancellor here, who more or less said, “You’ll always find reasons why not to go, so take it now.” The invitation was a joint one, jointly from Jesse Greenstein and from Lyman Spitzer. By this time I was becoming more and more interested in the magnetic problems.
I can see why Spitzer would be interested, from his own research.
Yes. I think that he hadn’t become interested in it to the same extent then. Though, it is true that there was a paper on the size of the galactic magnetic fields that was produced just about the year before I went over. Two rival theories, one originated in Princeton, the other one in Cal Tech, and I had to confess to Spitzer that I preferred the Cal Tech one!
I would like to have your point of view on the progress of work in stellar structure, from your QUARTERLY JOURNAL article you indicated how the computer changed things immensely, and if you have any comments further…
It wasn’t simply that. You see, F. Hoyle particularly and Martin Schwarzschild changed the direction of the advance from a business of constructing models into a business of deciding on the progress of evolution in the stars.
This was the problem of computing a model from first principles, as opposed to using the earlier models for the next step in evolution?
It wasn’t even as much as that. You see, till the theory of the energy generation became known, became established, it wasn’t possible to do anything much further than constructing ideal models. But that theory appeared in 1938—39, and immediately it had its effect. What would happen if you got exhaustion of the sources in the center? The thing that Hoyle started stressing, and other people as well, was: why were there such things as red giants? How could one manage to explain those?
So you had the problem of what to do with the helium and the exhaustion of hydrogen?
Yes. Now, the Russians, around about this time, were beginning to stress the possibility of having stars lose a lot of their mass, and evolve effectively as unmixed stars down the Main Sequence.
This is the old direction, Russell had that direction.
This is how the Russians figured it would work, by mass loss?
Yes. Parenago and Massevitch, to begin with. But having decided that they could get a model of a red giant, if one made an appropriate discontinuity of mass, they then turned to trying to see whether — instead of having a static picture — you could have a cinematic picture of the development.
This is Hoyle and Schwarzschild.
Yes. But the work developed in the early fifties, that sort of thing. Now, all the early work was done with a minimum of computational assistance, and then the two Bondis, Hermann Bondi and his wife, produced a rather ingenious method for getting models quickly, provided they weren’t too complicated. But as soon as you got to having actual energy generation figures, and actual opacities, things became too complicated. So there was a variety of models that were constructed by hand machines, but these were very laborious, and it was with considerable relief that people turned to electronic computers. By the time they got into computers, I stopped.
You stopped. Why?
Not having had enough time to master how to use a computer.
I see. Was it the availability of computers?
No. So far as we were concerned — I was at Leeds, — I was myself for some four years the supreme authority in regards to the computer. The day-to-day running of the computer was left to the director of the computing laboratory, hut if he wanted to appeal to the highest quarters, he was supposed to do it through me, and I was responsible for the organization, as from on top, in the university Senate.
So you didn’t apply the computer to stellar structure?
I had to learn the language and what the computer could do, but I didn’t learn to program it myself. Which was unfortunate.
Do you feel that you had the opportunity? Or you had other interests? You mentioned that you had some serious sickness at about this time. Or was it later?
It was about this time.
Could that have prevented you from pursuing it?
Well, it was the general feeling that I was overloaded with administration and so on. My connection with computers was administrative.
OK. So there’s no aspect of your direct association with problems of stellar structure that we haven’t at least mentioned?
I think not.
OK, so then, let’s go back to the thirties, and your work in magnetohydrodynamics.
Yes. Well, the first thing was, of course, this idea in the theory of sunspots. Now this is a point on which I’m not clear about credits. It was becoming clear that the sunspot equilibrium must be profoundly influenced by the sunspot magnetic field, and that is the way of getting a sunspot into equilibrium. If the sunspot is cool, normally you’ve got material from outside coming over, and swamping that cool material. But because it’s held back by the magnetic field, the sunspot is able to persist in equilibrium. Now, I didn’t publish anything, and I’m not absolutely certain which date, hut my impression is that this is one of the ideas that was being bandied about by Biermann and myself, in the year immediately prior to the Second World War. We were corresponding very vigorously, and doing each other quite a bit of good, I think.
What year would you place that at?
Do you have these letters?
No. But in one letter from Biermann, after we’d been chasing letters to and fro like this, he said, “I think that the coolness of the sunspot ought to be explicable in terms of the restriction of convection by a magnetic field. The prevention of convection.” And I started the letter saying, “I don’t think that’s right,” and proceeded to fit in numbers to show that it was wrong, and I finished off by saying, “I’m afraid this agrees with that you’ve been saying.” So anyway, I didn’t mention this except in a discussion at the Royal Astronomical Society during the war, when Thackeray produced a paper in which he said that there was nothing observational to suggest that there was convection going on especially in sunspot. And I mentioned that Biermann had suggested that there oughtn’t to be convection in a sunspot. Biermann himself published his result in 1941 in a place that wouldn’t have been noticed by anybody, if I hadn’t specifically drawn attention to it, in my publications.
Was this because it during the war?
Oh, I didn’t mention it until after the war, when I wrote to him and asked him whether he’d published this idea. He mentioned this short note in the VIERTELJAHRSCHRIFT DER ASTR. GBS. Then I felt free to mention this result as often as I could.
This is after or about the same time that Alfven had his magnetic braking mechanism which really was the same thing but applied to a different problem.
Alfven proceeded to apply the ideas to the theory of sunspots, but he reversed the order of causality. He said, “The sunspot is cool because of expansion of the magnetic field — that produces a coolness…”
Expansion of the magnetic field?
Yes. “That produces a coolness by adiabatic cooling.”
Did he base this on Biermann’s original papers?
Oh no. This was his own idea. He didn’t mention Biermann at all.
But this was during wartime, and I didn’t hear about it till later on. I had on a later occasion to draw attention to the fact that he had got the casualty the wrong way, hut I think that people have tended to attribute to him more than he actually had said. On the other hand, there’s a man by the name of Walen, a Swede, who succeeded in quarreling with everybody in Sweden, and ultimately with everybody in this country except Chapman.
Chapman seems to have been rather agreeable.
Yes. So Chapman was the only person who said to him, “Look, I’m not going to argue about your ideas. I’m going to treat you as a friend and leave it at that.” He was the only person who was able to get away with it. Anyway, Walen had the idea of the restriction of convection by the magnetic field, and did quite a lot on it. He in fact had to publish his work finally by himself, in separate private publications, because he’d quarreled with everybody else. He started off working on Alfven’s theory of sunspots, abandoned that, perhaps because of criticisms by myself, (I was extremely down on Alfven when I first read his work) but he then proceeded to quarrel with the big man on the evolution of galaxy, Lindblad. He proceeded to quarrel with Lindblad and blew up, especially when he was presenting a thesis for a doctorate and arrived in the examinations and discovered his internal examiners were Alfven and Lindblad and so, having quarreled with both of them (laughter)… Anyway, he produced some extremely sound ideas on magnetohydrodynamics in the sun, which because of the way in which they were published, haven’t received a great deal of publicity.
It’s interesting, when you try to follow up and find some of these publications.
I’ve referred to them for example in the article I wrote in THE SUN volume. 
That’s in the Kuiper and Middlehurst series?
Could we go hack and trace the development of how you at first rejected the dynamo theory, and then started developing it again?
I think I ought to mention just one thing before we get to that. Through Chapman, I became cognizant of work on the theory of magnetic storms. About 1942, I had a letter from — Chapman saying, “I’d like you to look up some work from Alfven that I’ve just received, in which he discusses a new theory of magnetic storms and the aurora.” Chapman had recognized that I was quite good at criticizing other people’s ideas, and he wanted me to have a look at this work from a critical point of view, because he didn’t believe in Alfven’s ideas, and he wanted somebody to pinpoint what the dubious points might be. This I did, and published a paper in TERRESTRIAL MAGNETISM in 1943, in which I first of all gave, at Chapman’s insistence, a fair presentation of Alfven’s work, which was likely not to be known simply because it was published in Sweden. And then I gave a criticism of it, in which I proceeded actually to carry some of the mathematics a little further and developed it, to show what were the correct ideas on which Alfven had based his theory, but pointing out that what he was doing was to consider a set of particles and not a plasma. You see a plasma as a whole is subject to cooperative processes, and he’d ignored the cooperative processes.
He’d conceived them as a set of particles.
Yes. And moving in a field that was hardly affected by their motion. It was that, essentially. Anyway, I had been always interested in the magnetic problems, ever since my first work on Chapman’s ideas, and I’d produced something on kinetic theory in these connections, but I remained reasonably convinced that you couldn’t generate a field by the dynamo process. I remained so until after the war. Towards the end of the war, I produced a paper in which I connected kinetic theory with ionospheric processes, and the conductivity of the sun’s atmosphere and such things as that, in the PROCEEDINGS of the Royal Society —
Let’s see, “Electrical Conductivity of an Ionized Gas in a Magnetic Field…” 1944 July it was received. 
Yes, that’s right.
You used Chapman’s velocity distribution method.
Yes. That’s right. It was actually Chapman who was partly responsible for it, because he said to me, at one R.A.S. meeting “You know, there’s a gap between two different approaches, and they get different results — the velocity distribution method and the free path method — they’re essentially different results. Can you manage to tidy these up?” Now, I proceeded to tidy it up to start with, and then the paper just went on like Topsy and “growed.”  But now, after the war, partly because of Alfven, I began to concentrate a little more on the magnetic fields in particular because of calculations of times of decay.
I think you’d been concerned with that for quite some time. You’re talking about the decay of the primordial magnetic field, on the order of i1o) years.
Yes, well, this was ‘46. Anyway, as far as sunspots were concerned, I started off more or less saying, Alfven’s theory ought to be wrong, because it isn’t reasonable for a magnetic field to produce blackness and so on. And you’ll find that I said just that effectively at the start of the paper, and then proceeded to show that the magnetic field must, according to observations, decay so slowly that you couldn’t imagine an idea of a magnetic field just being produced where it was. It would take too long to produce. So this brought me down firmly on the side of the magnetohydrodynamic generation, which was what Alfven himself would have believed in. Well, about that time, I began to make contact with a man called Bullard at Cambridge. He’s a geophysicist actually. He was starting to work on dynamo theory. He had hoped that one might be able to solve the problem of cosmic magnetic fields by some sort of fundamental theory, like that proposed by Lord Blackett, and then, when that had turned out to be wrong, he set to work more strongly, to try to develop further the sort of ideas that Elsasser had developed.
Now, so far as Elsasser was concerned, some of his ideas were perfectly sound, but he hadn’t been able to produce the final clinching argument. I was able to interpret to Elsasser the obviousness of certain of his conclusions which I had come to recognize — the production of toroidal magnetic fields as a consequence of non-uniform rotation. He was a little surprised when I produced this, and he asked if I was publishing it somewhere. I said, “No.” He said, “May I?” Anyway, I thought that it was too well know, in fact to call for publication. But anyway, electronic computers were just beginning to be available, and people began to welcome computers and to try to use them to establish that you might be able to produce a dynamo field, in circumstances which were excluded in my original discussion. As I say, my own work was as the anvil, because I proceeded to sharpen my original discussion, and establish other cases in which dynamo maintenance was ruled out, hut what it amounted to was, you couldn’t get a dynamo unless you had a flow that was sufficiently complicated which made it awkward even using computers.
And that was as far as I was able to take the analysis, in 1957.
That’s quite interesting. So as you say, you had gone as far as you could without computers. Or without using a computer.
I did make some tentative efforts to get into computing work. But they never got really to the interesting stage. Some of the recent work that’s being done on the dynamo problem has depended on rather more refined mathematics than was included in my original mathematical course, and with which I’m not particularly familiar. And I think, had I known the appropriate mathematical developments, I might have been able to produce results myself there. But — well — I’m afraid, effectively, I tended to dry up, in the middle fifties. The last thing I really feel that I’ve been proud of, in the astrophysical sense, was the little hook on magnetohydrodynamics in which I was able to put together all the ideas that had come to me, and clear away a large number of the doubts and difficulties that people might have had, and to point out directions of advance.
That’s the Interscience Track, and I’m interested in how you came to write that hook. 
Well, when I went to Princeton and Cal Tech, there was a sort of understanding that if I published anything, they would get credit for it, and there was a certain obligation to get something published if possible.
Was this a lectureship or visiting position?
It’s a visiting professorship, and I gave courses in both places on much the same sort of lines. In each case, it was on magnetic fields in astronomy. The first outcome was a paper in which I was trying to deal with magnetic variable stars, and came to the conclusion that the oscillation theories which were proposed by Babcock and by a Norwegian lady named Gjellestad (who worked under Rosseland’s inspiration) was unsound. That work was published in MONTHLY NOTICES, in the early fifties.  That’s the first thing. Then there was a COUNCIL NOTE written jointly with Babcock in which I don’t think I gave any acknowledgement, but in my article in THE SUN,  I was able definitely to give credit to people at Cal Tech and Princeton. But this had set me writing on the subject, and as a consequence, when I received an invitation from Interscience to write such a tract, I felt I could manage to get down to it, though it was a rather awkward business, because I had an ulcer, and was off duty, just about the time that I was finishing, after an operation.
Is this the first serious sickness which you mentioned?
Let me turn the tape over.
I was kept off duty for six months, by the surgeon, who felt that he’d got to have me tied by the leg, so I’d have to stay at home.
Not physically tied I hope.
No. But as a consequence, I was able to finish that article, for Interscience.
I see, so it was a good thing?
— because it gave me spare time. Actually, I produced a Presidential Report for the IAU, while I was lying in bed just before the operation, too.
There is of course a whole different aspect to your life, your personal life during all of these years, and also the fact that you’d been to a number of different universities. We’ve mentioned most of them but not all of them. You were also at Bangor.
Yes. After the war.
I see. I’m interested in how you got the various positions, and how you ended up at Leeds.
The Swansea one was more or less a case, of having to move.
Had that happened before?
That was the first case of having to move.
Yes. Now, in those days, you stayed on the same salary until you were promoted to a higher grade. And so, when after a couple of years I got married, I began to think of moving to somewhere else. And a move to Dundee in 1937 was simply to improve my status. But after one year in Dundee, somebody at Manchester must have inquired of Chapman and Milne for a person who could take a fairly senior lectureship and I was put forward, and so, I more or less got the place without a competition, after an interview. I stayed at Manchester all during the war years, from 1938 to ‘45. At the end of the war, they started getting places filled where people had been acting as stopgaps during the war and so on, and as a consequence, a professorship at Bangor became available. Bangor was a very small place and very isolated, but a professorship was not to be sneezed at, and I applied and against very strong competition, I may say, got the thing.
Who were the other applicants, did you know?
Yes. One was a man who came here, to the pure mathematics chair in 1947. There was also a man, Harry Jones, who was professor at the Imperial College for many years. Another man became professor at Southampton, and so on and so forth. It was a pretty good lot. Anyway, Bangor had got some attractions, but it was at the end of a very long railway line. It’s 250 miles to London, and the trains were very slow in those days, and I wasn’t too bound there, and my wife felt a little unhappy.
Where did she come from?
Like myself, from London.
You were married in 1935.
That’s right, yes. We’d become engaged when I moved to Swansea. Then this man (H.S. Ruse) who became professor of pure mathematics here suggested to an appointing committee that I might be approached, and I was appointed here. Again, there was no advertisement. It was a case of being appointed after an interview here.
What were your ideas for the growth of the department here? Do you have any in mind?
I didn’t have very many, because that was a time when universities, and our university in particular, were chronically short of funds. In the early fifties, the government decided to produce some expansion in the university, concentrating particularly on technological subjects in which mathematics teaching would be required. As an offshoot of the developments that were beginning to take place then, when the size of the university was about 3000, or just above that, the numbers began to grow, and the mathematics numbers likewise started to grow. Since then, it’s been more a case of planning piecemeal as emphases varied, and occasionally saying, “Now, this is where we ought to be doing so and so.” It was about ‘56 that we began to think of a computer in the university. It wasn’t too long after my operation. And then, numbers were increasing, and one began to feel the need to organize things in such a way that every student had got contact with somebody, instead of being a faceless mob.
So you needed more faculty?
Yes. Needed more faculty, and a different method of organization.
How much direction did you give? Did you get very involved? You mentioned there were administrative duties.
My friend Ruse, the professor of pure mathematics, was nominally head of the department, up to the time that he retired, and actually it had become a number of departments by that time. I was head of applied mathematics. But we still worked close together. The two of us were at Oxford together. We’d known each other ever since Oxford, and so it was possible for us to manage affairs informally. One would bump into the other and say to the other, “I think it’s time we started thinking about so and so.”
So you had rapport, the two senior men in the department.
Was this ulcer also induced by anything professionally, to your knowledge?
It’s conceivable that it might have been. I had had a pretty heavy year. I was Dean of Science that year, and I also, earlier in the year, went to Russia on a visit. It was a visit six months or so after the death of Stalin, when they were opening the country to start with, and they couldn’t do enough for one. But the trouble was, that meant that you’d start off fairly early in the day, and you’d go visiting this and that, and finish up at the ballet, or dining till late in the evening.
Was this also the rededication of Pulkovo?
That’s right. Yes.
I see. What was your impression of Russian science as it was developed then?
There were two things that were obvious. The first was that they’d got to make a recovery from the ravages of the war, and they had done reasonably well, but there were still very obvious signs of war about. The second was that they were concentrating on particular lines, and where they concentrated, they were doing very good work, but there were an awful lot of gaps in between. It was the equivalent of what I saw in Leningrad, of a single woman going out to see if the road was in proper condition and carrying a sledge hammer with her. That was the sort of equivalent. Where they concentrated their efforts, they had to be respected. But there were gaps.
Did you meet Ambartzumian and people like that?
Yes. I can remember Ambartzumian giving a lecture, and we were supposed to have an interpreter sitting beside us and telling us what he said. And after a certain length of time, the man said, “I can’t do it. He goes too fast and it’s hard to understand his Russian.”
The translator was Russian?
Yes. He was a person they’d got in for the actual visit. He was quite fluent English speaker. He’d spent some time in this country, and his prime job was a translator of works like Dickens.
So he was out of his element, I take it, as far as technical jargon and stuff like that goes?
What about some of the astronomers who knew English, from Russia?
The two people I’ve known best over there have been Severny and Massevitch. Massevitch: I can remember her first appearance at the IAU at Rome in 1952, where she was acting as interpreter, when interpreting was required. Since she was young and very fresh in those days, she had a lot of applause for it. Severny: I had proceeded to referee one of his papers before the war, for MONTHLY NOTICES. It was his start. But of course after the war, he moved over from theory, which he’d been concerned with, and he was told to get on with developing the Crimean Observatory. He was one of the people on whom the Russians were concentrating their efforts, with an obvious real advantage. Severny was able to adapt Babcock’s magnetograph, and as Babcock began to he involved rather more in administration, Severny was gathering a group round him, concentrating on the same line of research. Now, I met Severny the first time at Rome, again. I didn’t say very much to him then, but we became quite good buddies as the time passed. Of course, the last I knew, he too was reaching the stage of feeling the strain of existence. After I retired here (retired officially in 1970) in 1971 they had a seminar, or group of seminars on magnetic fields in astronomy. A symposium, I suppose you’d say.
This was at Leeds?
Yes, it was a private University of Leeds retirement function. Severny very kindly came over and gave a talk. We just had two or three people that we were able to invite over. Paul Ledoux (I’d met him during the wartime in London, and we’d become friends ever since) and Ludwig Biermann came over too.
Talking about wartime experiences, you mentioned you were in the —?
Air Raid Precautions, ARP.
Did you have any defense research and development work that you were involved in?
No. As a matter of fact, there was one particular problem that they were trying to develop at Manchester, in electrical engineering, to deal with wave guides. It was really the sort of research that one carries on, or that could have been done, lust as well in peacetime. And I was able to produce a little hit of assistance in the interpretation of these results. Then also there was a point at which I was asked to consider a particular problem in propagation of radio waves.
Who asked you that? Bondi?
No. It didn’t involve moving away like it did with Bondi. I can’t tell you straight off, I’m sorry, another of these bad memories. But I produced one suggestion. Then I was told this didn’t seem right, judging by the recipient’s response, and then I got the correct solution and sent it off, and expected then to be receiving further information. And to my surprise, nothing ever came through. I met the man (Pigott) who’d been responsible for the original invitation a good deal later, and he said, “you had some contacts that were regarded as suspect, and the instructions were that nothing was to go to you.”
Did he ever identify those contacts?
No. But there were at least two people. There was Janossy, a worker on cosmic rays at Manchester. He was an escapee from Hungary, Communist, who returned there later. I met him in Moscow, when I was there on the same occasion at Pulkovo Observatory. H e may have been one. Then there was the minister of the church that I attended. He was a person who was a very keen pacifist.
When did you learn this?
Oh, about ‘47, after the war.
That’s fascinating. Well, you continued administrative work that you were involved in as a member of the large telescope users’ panel of the Science Council. This brings up a question that would lead to this, and it pretty much is a request for an overview from you of the growth and progress of astronomy in Britain, especially the question of the use and need for large telescopes.
Well, let’s see. There was a proposal to establish a large telescope quite early on after the war, and the minor blank was provided by the University of Michigan. It was a blank of which they couldn’t make any use. Put the telescope people began the preparing of it the figuring of it, and then a clamp down happened, because of the absence of funds.
When was this?
Somewhere about 1950. It had taken place by the time I went to Princeton and Cal Tech. But one didn’t know how long it was going to be. The Royal Observatory, the Greenwich Observatory in those days, was under the Navy. And naturally, the Navy, when it was a question of priorities, regarded the ships as taking priority, and the Observatory took the cuts. And it wasn’t till some years after that, that the question of having a large telescope came up again. Some people suggested that Spencer-Jones, the Astronomer Royal, might have bowed a little hit too early to the storm. Certainly when R.V.D.R. Woolley, came, as Astronomer Royal, he refused to be silent and soon had got things stirring again. But there was a feeling, in those days in this country, that the thing that one could do best in this country, particularly with the skies that we had, was theoretical astronomy, and it wasn’t necessary to have the observational work. I think that this was advocated especially by the big spenders in physics who were concerned with research in nuclear physics and such things as that.
It certainly is acknowledged that Britain was the leader in theoretical astrophysics throughout this entire period. Yet it was the nuclear physicists who were using that as a reason for playing down observations?
They were doing so. Yes.
Who was doing that?
Well, people like Blackett, for example. At Manchester, where Blackett and I both were, they had a telescope on top of the physics building at one stage, and they said that, every now and then, somebody got an idea of using the telescope. He would spend six months getting it going. Then his interest changed to to something else and it and it remained unused. The skies were too bad. It was really a serious question. Having seen the way in which the Princeton and Cal Tech people married the theoretical and the observational sides, I began to feel some doubt about keeping them apart. I remember once upon a time asking Milne, when I was a research student, should I try to learn something of observational astronomy at first hand? He said, “Don’t try to observe yourself, but acquaint yourself with the results the observers are deriving.” I think that that was perhaps a wrong piece of advice, to the extent at least that only somebody who knows first what the observers are doing can properly make use of theoretical ideas. Anyway, the Isaac Newton telescope was finally erected. There was also a telescope which, before the war, moved from Oxford to South Africa, the Radcliffe Telescope.
While I was up there it was still active in Oxford, and it was suggested it was desirable that that telescope should he moved to a place in the Southern Hemisphere, where things weren’t so full up in any case, and the seeing would be better. Anyway, that telescope had fallen on thin times, because of money. There was also the Cape Observatory that was run by the British government, and it was felt that we needed a committee that could organize the use of the new telescope (the Isaac Newton), the Radcliffe Observatory, which was now becoming supported by the British government, and the Cape instrument. That was the origin of the Large Telescope Users committee. But the committee wouldn’t have come into existence but for the effect of administrative changes. First of all, the Greenwich Observatory had become an independent institution under the Science Research Council. Also people had succeeded in convincing a certain number of higher ups in the Science Research Council that observational astronomy was a must. It must be provided with support. Well, since then, there’s been a steady development of observing facilities, culminating shortly, one hopes, in the institution of a base in the Canary Islands, in addition to the Anglo-Australian telescope.
Let me ask you how you became involved in this directly, as a theoretician?
It was more a case that I had got to know Woolley rather well, and he felt that it was desirable to have a really strong committee at the start, people whose opinions could he relied on. Later on, when the thing got going, it would be easier to carry on along accepted lines. So it was lust for that reason.
The only thing that I can remember my own particular training coming out in, was one particular problem where a man was wanting to work on infra-red, and I had done some work on the infra-red radiation in the earth’s atmosphere at one point. I was able to provide the justification for his statements.
That’s very interesting. That’s certainly very important, nowadays, in British observational astronomy.
I want to thank you very much for this session.
MN 90 (1930) p. 140.
It was actually the second stability paper.
MN 94 (1934) p. 39 for sunspot fields. MN 96 (1936) p. 15 for the structure of sunspots.
The paper actually was in Pub. Oslo Obs., Nos. 1 and 2, 1931.
MN 94 (1934) p. 768.
MN 96 (1936) p. 42.
MN 98 (1938) p. 734.
MN 101 (1941) p. 367.
QJRAS 7 (1966) p. 121.
"Solar Electrodynamics" in The Sun (Chicago, 1953).
Proc. Roy. Soc. Lond. A. 183 (1945) p. 453.
The allusion is to "Uncle Tom's Cabin," where Topsy is asked, "Who raised you?" and she replies "I just growed."
Magnetohydrodynamics (Interscience 1957).
MN 112 (1952), p. 527.
"Solar Electrodynamics" in The Sun (Chicago, 1953).