Oral History Transcript — Dr. Nicholas Kurti
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Interview with Dr. Nicholas Kurti
Nicholas Kurti; November 22, 1972
Abstract: Family background and early education in Hungary (Ferenc von Kármán). Undergraduate studies in Paris from 1926 (Jacob Salpeter, Felix Ehrenhaft and Paul Langevin); work habits, comments on Prof. A. Guillet, 1928-1931. Studies at Universitaet Berlin, 1929-1931, Max von Laue's weekly seminars; moves to Universitaet Breslau with Francis E. Simon; thesis, "The Thermal and Magnetic Properties of Gadolinium Sulfate," 1931. Social and political climate in Breslau, 1931-1933. Peter Debye's low temperature proposal to Simon (William F. Giauque); Simon and Kurti emigrate to England in 1933; Frederick A. Lindemann's (Viscount Cherwell) involvement; Imperial Chemical Industries (ICI). Settling down at Clarendon Laboratory, Oxford; discussions of their work on production of very low temperatures, production of liquid helium in 1936; the technique of detecting superconductivity in cadmium, 1934; comments on relationships in the low temperature community (the two groups at Clarendon). Collaboration between Clarendon Laboratory and Laboratoire du Grand Electroaiment, Bellevue, 1935-1939; leads to important prewar work. Comments on Leo Szilard and on colloquia and seminars at Clarendon Lab. Also prominently mentioned are: Hans von Halban, Hendrik Anthony Kramers, H. E. Kuhn, Heinz London, Kurt Mendelsohn, Otto Roff, Erwin Schroedinger, Wiershma; and Université de Paris.
Session I | Session II
Weiner:Today is the 22nd of November, 1972. This is Charles Weiner talking with Professor Nicholas Kurti as a continuation of an interview which took place on September 11, 1968, ending up with the promise that we would continue it some time in the "near future." By definition, it is near future now. We are talking in my office in New York. I would like to ask you first if you have any comments on the transcript of the first interview as you saw it.
Kurti:I went through the first 12 or 13 pages. I put in a few corrections, and on a few occasions, I even altered the actual text because I thought the meaning didn't come out right. But, apart from that, I didn't try to polish up the style or anything like that, I hope to finish my correction of the transcript, not during my visit to New York, but in the next few weeks.
Weiner:Perhaps on the plane on the way back.
Weiner:When we left off we had taken you up to the point of your arrival in England. We had discussed that Simon had gone over earlier and made arrangements with Lindemann in Oxford, that Mendelssohn had gone over to set up some of the equipment and had planned to come later but in fact came a little earlier than he had originally anticipated because of the developments in Germany, Simon arrived on August 20; you arrived on September 15. I would like now to trace the sequence of events and your reactions to them, starting off with the question: Did you proceed directly from Berlin to Oxford, or did you make any stops?
No, you see what happened was that I left Breslau I think about June or July, 1933, and went back to Hungary where my mother and my sister and my relatives lived. And then, round about the 8th of September, I left Budapest and first of all went through Breslau where I had spent the previous two years — I think I had still to collect certain material or something for Simon. And then I spent a day or two in Berlin, from there I went to Paris, And I arrived, via Dieppe, in London on the late afternoon of September 15, which I am almost certain was a Saturday. In those days it was not very easy for visitors, especially from Central Europe, to get through the British Immigration.
One thing created quite a lot of difficulty with me, namely, I showed very proudly a letter from Lindemann saying that he managed to get a grant of 250 pounds for me to come to Oxford and work at the Clarendon Laboratory. The Immigration Officer immediately said, "Professor Lindemann has no right to give you a grant; you haven't got a labor permit." As a result, I was given a permit to stay in England for about one month provided that I registered immediately with the police, Well, I wasted a certain amount of time. As a result I didn't get to Paddington Station until about a quarter to eight, where I had my first cup of English tea. And believe it or not, that tea in Paddington Station was probably better than any tea I ever had before. I don't know whether this would be true today. I remember I caught the 8:10 train to Oxford, I was going to stay with Mendelssohn, certainly to begin with, and I originally wrote to him that I would be arriving in Oxford round about 9:00 in the evening on the earlier train, which I missed.
Anyway, I thought I would somehow find my way from the station to Mendelssohn's, Well, I sat on the train, and I knew that the train was due in Oxford round about 10:00, Just before 10:00 the train came to a halt, and I looked out. There was a funny wooden shack of a station, so I said, "Oh, the train must be late, this can't be Oxford," I had in mind Oxford is a little gem of a university town, it must have a respectable looking railway station, And what I saw was really just a wooden shack, worse than some of the small stations in Hungarian villages. But then I looked out again and I noticed a little sign "Oxford," so I scrambled out of the train and I eventually got a taxi which took me to the Mendelssohns' house.
I didn't see anything of Oxford that Saturday evening because it was dark. And next morning it was one of those beautiful autumn days which I think you only find in England. It had been raining I think during the night, and in the morning, the sun was shining. Round about half-past nine or ten, Mendelssohn said, "I will show you Oxford," I got on the pillion seat of his motor-bicycle and he drove me down, Well, on Sunday morning, even today Oxford is fairly empty, but in those days it was completely so, There was hardly a soul on the street, And there we were going through wonderful streets lined by wonderful buildings, with the green lawns and so on.
And after this quarter hour's ride, I suddenly said to myself, "Well, why don't I stay and spend the rest of my life in England and in Oxford?" — an idea which never occurred to me before, Although I loved Paris, I never thought of settling in Paris, or settling in France, I didn't like Berlin very much although it was intellectually very exciting and stimulating, but I never, never thought, even before the Nazis came to power, that I would want to live and settle in Germany. And that first visit to Oxford immediately gave me the idea, here, this is the country, this is the place I want to stay in, Now I don't know if the same thing would have happened if my first visit in England had been, shall we say, to Leeds or even to Sheffield instead, But Oxford was wonderful, and that is where I stayed for the rest of my life.
Weiner:Let me stop at that point just to check, (Interruption)
Weiner:What did this kind of emotional psychological reaction mean - how old were you at this time?
Kurti:In 1933, I was 25 years old.
Weiner:So when you say the rest of your life, it was still a useful decision it didn't mean you were going to retire to this locale but that you were making your life there.
Kurti:That's right making my life,
Weiner:What was the reality in terms of making your life? What were your expectations, because after all you came as part of Simon's group, and his own position wasn't all that secure?
What happened was that Simon arrived in Oxford with just his own not-very-high salary on this ICI grant, with one collaborator that was myself - and with two or three cases, packing-cases and suitcases, of apparatus, I don't think I mentioned in the previous interview that on the whole the German customs authorities were quite decent, Some of them were the old-fashioned civil servants and they were quite helpful. Simon got the permission from the Ministry of Education (Kultusministerium) that in exchange for certain things he left behind, such as his office furniture and various other things, he was allowed to take out of the country some scientific apparatus.
So, in fact, he arrived in Oxford with, I think, one or two small helium liquefiers. I remember the one small helium liquefier which I built for my D. Phil. work in Berlin and which I used afterwards in Breslau - that was exported to Oxford. Then another helium liquefier based on Simon's then new adiabatic expansion of helium principle was brought with us, and then quite a lot of auxiliary apparatus - electrical instruments, gauges, stopcocks — because we knew that Clarendon Laboratory, like most physics laboratories in those days, had a very meager budget, and Simon and I were very keen to get the work started as quickly as possible, Therefore we took practically all the material that we needed in order to get research started with us from Breslau.
Weiner:Well, there was no tradition of that kind of research at Oxford.
Not that kind of research exactly, You see what happened was that — Lindemann, having been a research student of Nernst, was always interested in low temperature work, and he, in fact, bought from Simon a hydrogen liquefier, I think in about 1930 or 1931, which was installed in the Clarendon Laboratory and was used by one research student who did some experiments or specific heats at liquid hydrogen temperatures. And because Lindemann was interested in low temperature work, he then later bought, again from Simon, a small helium liquefier, a so-called expansion helium liquefier, which Mendelssohn took to Oxford in January 1933, I believe it was on the 5th of January 1933 that the first liquid helium was produced in the British Isles — not in the British Commonwealth, or the British Empire as it then was, because MacLennan at Toronto had already liquefied helium.
There's a very amusing story about it — that was done in a room in the old Clarendon Laboratory, which was built in 1872, and which after the war was somewhat rebuilt and made into the department of geology. And I think a few years ago Mendelssohn went over to the geology department, He wanted to look around and see what happened to the old rooms, He was not really offended but he came back and said, "This is shocking, The room where I liquefied the first helium in the British Isles is now used as a gentlemen's lavatory," One of my colleagues, Dr. Arthur Cooke, said, "Perhaps we should put up a memorial tablet with the inscription, "In this place Dr. Mendelssohn passed liquid helium on January 5th, 1933,"
Weiner:That's very good.
Kurti:Anyway, the important thing was that we had with us all the wherewithal for setting up apparatus and starting scientific experiments. I found the going a little bit tough, mainly because my English was very poor. Although I learned German when I was three and French when I was eight, I only had English lessons for two years between the ages of 16 and 18. When I got to England I could read English. I did understand a little bit and could make myself understood, but it was very, very tough going. Still, to some extent, I regret I never took formal English lessons, I really learned it the hard way. If I had taken lessons I would have gotten a better command of English quicker, but I didn't want to spend time on language studies. Anyway, with some technical help and myself doing quite a lot of glass-blowing and soldering, my helium liquefication liquefier,which I used in Berlin and in Breslau was put up by about December '33 or January '34, and we started experimenting, I am not quite sure to what extent I mentioned the actual scientific work I had been doing in Breslau and Berlin.
Weiner:You mentioned your thesis and the fact that you continued it in Breslau, You told how you first got interested in the statistical problems.
What happened was, as I think I explained before, we never did any adiabatic demagnetization work, That means the production of very low temperatures by the method originally proposed by Giauque and by Debye and first carried out in March and April 1933 by Giauque and MacDougal in Berkeley, California, and by De Haas, Wiersma and Kramers — Kramers being really the theoretical brain behind it — in Leyden. One reason was that Simon, who was very friendly with Giauque, told me that since Giauque himself suggested the method and developed all the apparatus for doing it, it would be to some extent ethically wrong to try to compete with him.
I remember that I came across a letter which he wrote to Meissner in Berlin where Meissner kind of sent his condolences to Simon about having lost the race producing low temperature by adiabatic demagnetization, and I remember Simon's reply where he said, "No, we didn't want to do it because, after all, Giauque was already preparing this experiment." I remember he said it in German, "Wir wollten warten bis der Giauque damit heraus gekommen ist." — that is, "We wanted to wait until Giauque has done it." But once we got to Oxford, he said, "All right, let's do it, After all, we, as it were, predicted what should be the effect, and in fact our prediction which was made a few months before the actual experiment proved to be correct.
We have a certain justification in going ahead, especially since the priority is now definitely Giauque's and De Haas'," So we set up the apparatus, and as Simon said, "Let's now see how we can use this new method of producing low temperatures, not just for the sake of producing low temperatures, but to study the properties of other materials at these temperatures." And the first, probably the most interesting problem was to see whether certain metals which did not become superconductive when cooled down to about one degree Kelvin, which is a temperature that could be reached with liquid helium, might become superconductive when cooled into this new temperature range that was well below one degree Kelvin, So we set up this apparatus.
There was one problem and that was to get a magnet. For instance, Giauque, for his experiments had a solenoid powered by several hundred kilowatts and producing a field of about nine kilogauss in a very large volume, De Haas and Wiersma in Leyden had a very large electromagnet built by Siemens which could produce, I think, about 25 kilogauss in a gap of probably as much as 5 or 10 centimeters, The only magnet we had in the Clarendon Laboratory at Oxford was an old horseshoe magnet which must have been made at the end of the 19th century, which produced a field of four, five or possibly six kilogauss in the space we needed, Fortunately, we had a quite good power supply for it because the Clarendon Laboratory had a very good hundred kilowatt DC generator which was used previously by Dr. A. C. Egerton, who later become Sir Alfred Egerton, who was Reader in Thermodynamics in Oxford in those days (and in fact, Simon succeeded him as Reader in Thermodynamics when Egerton went to Imperial College in London). Anyway, this generator had been used by Egerton — I don't remember now for what experiments — but it was no longer needed by him so we could use it for energizing this and our future electromagnets.
So we had this generator and we had helium liquefication apparatus; we had a magnet. First of all, we decided to try to use other substances for the adiabatic demagnetization. It is very interesting that Giauque used gadolinium sulfate because that was the substance which had been shown by Kamerlingh Onnes and Woltjers some 15 or 20 years earlier, that it behaves even at the temperature of liquid helium as an ideal paramagnetic substance, that is, a substance in which all the elementary magnetic dipoles are entirely free from each other, do not interact with each other — and therefore have a big entropy even at one degree, which then can be reduced by application of a magnetic field;therefore such a substance can be used for producing low temperatures. On the other hand, it is very interesting: that in Leyden they used a cerium salt, cerium fluoride, and that for also a very interesting reason.
Kramers was the originator of the famous Kramers theorem which said that if you have a system in which the number of electron spins are odd, then that system always retains degeneracy, that is, disorder with respect to spin orientation, of two. In other words, whatever happens, whatever influence the electric field of the crystal or anything else may have, you still have even at absolute zero — provided the spins are not interacting with each other — a twofold degeneracy.
The spin can point up and down and still have the same energy. Then they said, now, cerium is the first rare earth element and it was known that at low temperatures it has effectively a spin equal to one-half, and therefore that would be an ideal substance to produce low temperatures. What we did, we decided to try to find some less outlandish substance, a substance that one could readily obtain from any chemical firm, We looked at the old Leyden measurements on various other paramagnetic salts and we found that both iron ammonium alum and manganous ammonium sulfate — seemed to behave fairly ideally at the temperature of liquid helium, and since they were so much cheaper and so much more easily available, we decided to try those.
And, in fact, we first of all used manganous ammonium sulfate, That was our first experiment in Oxford on adiabatic demagnetization. We found that on demagnetizing manganous ammonium sulfate we could reach a temperature, which we calculated by measuring the magnetic susceptibility and assuming in the first approximation that Curie's Law (that means the inverse proportionality of the absolute temperature and the susceptibility) is still valid, we reached a temperature of the order of a tenth of a degree, Then we said, now let's see whether we can find some new super-conductors by cooling certain metals down into this temperature range.
We thought we should first try one of the most generally available substances, so we tried copper. Nothing happened. We didn't find any superconductivity. And then we said, all right, we will now try cadmium, which we had a good hunch should be superconducting. And sure enough, we did the experiment — sometime in February 1934, I think — and from the very first experiment we found, indeed, that cadmium became a superconductor. The method of measurement, the technique of detecting the superconductivity was also quite interesting. In order to produce these low temperatures, we had this paramagnetic salt which was first of all powdered and then compacted into a little cylinder and placed into a container which was cooled to about one degree Kelvin by liquid helium, in a magnetic field, and then this cylinder of paramagnetic salt was isolated thermally from the surroundings by removing the helium gas which served for thermal contact during the stage of magnetization (when a certain amount of heat is involved), and then the magnet was removed; the paramagnetic salt cooled; and the temperature was measured by determining its susceptibility.
That was done by a set of mutual inductance coils surrounding the specimen and kept at liquid hydrogen temperature. There was no possibility, in those days, to have a length of wire of the material put into the apparatus and connected by leads to the outside, so that you could actually measure the disappearance of the resistivity. However, it was known by then that a superconductor behaves like an ideal diamagnetic substance. In other words, if you put a superconductor in a magnetic field which is not high enough to destroy the superconductivity, then the magnetic induction does not penetrate into it - it repels the magnetic flux, in other words has a very high diamagnetic susceptibility. So we said, let us measure the total susceptibility or the total magnetic moment of our specimen, into which we embedded some cadmium or some other material whose superconductivity we wanted to determine.
So what we did, we mixed up powder of the paramagnetic salt manganous ammonium sulfate — and powdered cadmium, then compressed it, put it in the apparatus. We knew that because of this intimate contact between the cadmium grains and the salt grains the cadmium grains would also cool to the low temperature. And we demagnetized the salt. We knew roughly what sort of susceptibility we should have reached under those certain conditions, And lo and behold, we found that its susceptibility was very much smaller in fact, it was of the wrong sign because the paramagnetic salt had a positive paramagnetic susceptibility, the cadmium becoming superconductive, had a negative susceptibility. In fact, after the demagnetization, we found that our galvanometer deflection, which gave us the measure of the susceptibility, was in the wrong direction.
And then all we had to do was to allow the specimen to warm up and measure the susceptibility, and we noticed first of all the susceptibility sort of decreased slowly because the paramagnetic salt susceptibility decreased as the temperature rose, whereas the cadmium susceptibility remained exactly the same, because it remained superconductive. We used a very small field, and finally when we reached the point at which the cadmium ceased to be superconductive, then suddenly the susceptibility jumped up from a negative value to a positive value and in this way you could even determine the temperature of the transition point. We found 0.6 Kelvin and since then there have been many more determinations of it and I think the accepted figure now is .54, So we were only out by about 10%. That was, I believe, the first instance that such a measurement was done.
Weiner:This was published in 1934 in Nature then.
Kurti:That's right, in March.
Weiner:Simon and Kurti, "Production of very low temperatures by the magnetic method: superconductivity of cadmium" Let me ask about this, You described the technical details and very often in it you said, "We then decided" or "We did this" Now, first of all, over how long a period of time? Secondly, what style of work discussion as you were working, discussion after hours, were there others involved in the discussion, was it private thinking, was it doing and not thinking I'd like a feeling of the actual work?
First of all, let me explain that when Simon and I arrived there, literally we were the only two people. We worked together. Simon had also a research student when he arrived, a young Englishman called B. V. Rollin, who rather tragically died a few years ago. So that was our group - Simon, myself and Rollin, Simon immediately detailed Rollin to start on his own and work on a thesis, mainly I think on the properties of liquid helium, So all this adiabatic de magnetization work was done by Simon and myself, During a certain period Heinz London, who at that time spent a little time in Oxford, did work with us in part, He helped us and we discussed things with him, but he was not really deeply involved in this work.
The method of working was very informal, I saw Simon pretty much the whole day, every day, In those days I was a bachelor, and in fact, the Simon household was almost a second home to me, Twice, three times a week, I would just arrive, appear there, have dinner with them, and after dinner we would discuss things about experiments. The actual experiments were carried on simply by Simon and myself. In those days you had to wait for pretty well the whole day in order to get your liquid hydrogen which you needed to liquefy your helium, and the experiments started very often at about nine or ten in the evening and went on until about next morning at five or six, Simon was always present, and as we did the experiments he was very keen on working up the results as they came along.
I took the readings and he wrote them down and was very keen on drawing graphs immediately to see what was happening, "Now what do we see here?" And usually once one experiment was completed, the next day we would go over the result and decide what would be the next one, The apparatus would be taken to pieces and conditions changed. So it was a continuing process, merely between Simon and me continuing discussions, altering the apparatus, exchanging ideas, improving the techniques, seeing what new materials to investigate.
Weiner:What about contact with other people working on the same general area? Were you in correspondence from the time you arrived in Oxford? It would be more that Simon as the senior man would be the one in correspondence.
Kurti:Well, we were in contact not so much with Giauque because somehow Giauque's interests were not as wide-ranging as ours, Giauque was very keen on doing really good and very accurate measurement on the thermodynamic and magnetic properties of one substance, gadolinium sulfate, That was his main interest in those days, But we had more contact with the Leyden people who were interested in other substances, interested also in the actual technical aspects — technical from the point of view of producing low temperatures — of the magnetic cooling method, So they knew what they were doing. There was a very friendly collaboration with them, Where do we go from here?
Weiner:Let me ask a question on that. Now that the Simon papers heve been preserved — and thanks to your efforts, organized and cataloged, have letters exchanged with Giauque and other people turned up in the collection?
Kurti:The trouble is, you see, I frankly, believe it or not, have not looked at the Simon letters since they were properly cataloged. And previously they were in very big boxes and I never really went through them, Therefore, although I am quite sure there are a number of letters — I found some of them when I was interested in certain things — but I have not really gone through the Simon correspondence of '33, '34, '35, '36, But I am quite sure there are quite a number of them.
Weiner:It would be interesting as a supplement to what we are doing to then identify specific letters that relate to the things we are talking about to fill in certain details.
Kurti:Well, look, if you like, it is a good point, when I get back to Oxford, one day when I am up in London at the Royal Society, I will look through these boxes and just see how they fill in.
Weiner:It would be very helpful. I want to trace the research, just in the way you are describing it, but let me set the stage a little bit by asking some general questions on Oxford, For example, you brought a good deal of the instruments and the set-ups that you needed but there were other things that you had to obtain locally, What were the facilities at Oxford? What was the relative ease of obtaining the materials you needed? Were there any problems with budgets and things for these materials? The period we are describing is from September '33 up through those first several years.
The period up to about 1938 or '39, till the war. On the whole, in common with all scientific laboratories in universities, the Clarendon Laboratory was very low on funds, But fortunately Lindemann was quite good in getting modest funds for certain research, For instance, in the late thirties I am almost certain that Lindemann got us some funds for instance from the Royal Society's Parliamentary Grant-in-Aid.
But apart from that it was very tough. Just to give you an example, we normally didn't buy tap grease. It was too expensive, But Lindemann was a very keen golfer. And he didn't like to use old golf balls. So he presented his old golf balls to the Clarendon Laboratory. They were then dissected — and golf balls contain a lot of very high grade latex rubber. We bought cheaply some lanolin and then we set up a little vacuum apparatus and we heated the latex rubber and lanolin together under vacuum and finally what we got was a quite high quality tap grease — what I think is called Ramsay grease — and very often this was the grease we used, homemade grease. Some of the basic apparatus was there — helium compressors had been installed earlier in the Clarendon Laboratory — we had gaseous helium available, We could get liquid air and hydrogen was liquefied in the apparatus installed in about 1931.
There was a quite good mechanical workshop and in fact the one thing that Simon got when he arrived in Oxford — fairly soon afterwards, was an additional mechanic who was mainly concerned with low temperature work. His name was Milligan and he actually stayed in the Clarendon Laboratory until he retired, He came to us from Cambridge where he had been employed by the Cambridge Instrument Company, It was rather amusing that when he retired from the Clarendon Laboratory he joined, as one of the first employees, a then newly-formed company in Oxford, the so-called Oxford Instrument Company, founded by Martin Wood, And he was obviously very proud of the fact that he was probably the only mechanic in the whole world who was employed both by the Oxford and the Cambridge Instrument Company.
So it was not too bad. We had quite good mechanical help, but it was probably an invigoratingly tough existence, We had to do a lot of the things ourselves. The room where I set up my helium liquefier and where we did the demagnetization experiments was a dark room. The walls were just old brick which had never been cleaned since 1872 when Clarendon Laboratory originally was built, And I remember it was I think during the Easter holidays of 1935 that I got so fed up with the darkness of this room that I decided to lighten it, And I spent the Easter vacation whitewashing the whole room — all the walls and so on — so that it looked a little less somber.
Weiner:I know that in the biography of Simon and in some of the letters that are quoted, he complained about the lack of facilities and that the very physical features of the building which you described were not only depressing, but rather limiting in terms of research. And this bears it out. What about the status of the group as a group — well, you are talking of two or three people working together — but what about the existence of the group within the larger Clarendon circle? After all, there are other physicists (and presumably people in other sciences, but I presume they are pretty much physicists) working in that same laboratory. How were you received as a group and as an individual? How did the group relate to the other groups?
The Clarendon Laboratory had a number of small groups in those days. It is very interesting that unlike the Cavendish which under Rutherford developed itself into one laboratory devoted to merely one large and very important subject. Lindemann said that the Clarendon Laboratory should be a laboratory in which all physics is the subject. To some extent it was not a very effective way but, on the other hand, it gave fantastic variety to the Laboratory.
There was infrared research, there was nuclear physics, there was low temperature physics — I don't know what else — there was some work in photo cells, there was very good optical spectroscopy work going on under D. A. Jackson and H. E. Kuhn (who came from Goettingen). So it was a laboratory with something like eight or nine individual groups or individuals working in certain fields,quite independently. And on the whole — not even on the whole — the reception of the Central European emigres was marvelous. We were treated with utter friendliness and all our colleagues went out of their way to help us in every way they could. We were really treated as very welcome visitors. And they were interested in our work. We were interested in their work. It was a very friendly atmosphere.
The number of researchers, including staff and research students, was never more than about 15 or 20 — and we always met for tea and knew each other and helped each other, There was no difficulty. I should explain perhaps one thing — that there were really two fairly separate low-temperature groups in the Clarendon Laboratory. When Mendelsohn came over — he came over before us — he felt that he would be entirely independent from Simon and he had his own little group of people, and his own rooms, And there was also some sort of a gentleman's agreement that Simon and I and others in our group should not work in the particular field in which Mendelsohn was working. His main interests were liquid helium and superconductors.
There was a bit of friction when we looked for superconductivity in cadmium but we felt that although it was superconductivity it was using an entirely novel technique so that to some extent it was justifiably in our domain. There is one thing that I might mention which I think — I dont know to what extent and when this interview will be used — but there was a fair amount of friction during all those years, both before the war and to some extent after the war, between Mendelsohn and Simon, I don't want to go into details but I want to explain how it came about and why.
You see, Mendelsohn went to Oxford in early 1933 — he was an extremely able man, a most excellent physicist and very effective, he got things done very well — and his obvious hope was (it was a reasonable hope) that when he came to the Clarendon Laboratory he would be the low-temperature physicist at the Clarendon Laboratory. And he would eventually build up a big laboratory which perhaps will rival Cambridge. Then, with Simon coming to the Clarendon Laboratory, this was no longer on, because Simon was senior to him and was a well-established low-temperature physicist and it was quite clear that certainly for many years to come, it was out of the question for Mendelsohn to be the head of low-temperature research at the Clarendon Laboratory. So what happened was this — Simon never said that he was the head of the low-temperature section.
He always agreed that Mendelsohn should have his own independent group. But somehow or other, I think many of these frictions were due to this fact that Mendelsohn felt that if only Simon had not come to the Clarendon Laboratory, his position would have been much stronger and probably from every point of view his advancement, I think, would have been more rapid. I was very sorry to have seen many of these frictions — some of them were rather unpleasant and worried Simon — but I mention this because I believe this is the basic explanation for it.
Weiner:How did it affect your relationship with Mendelsohn?
Kurti:Obviously, we had our little tiffs, because sometimes you cannot help it when you have this sort of rivalry. You cannot help having certain difficulties, but finally, I think, we sorted them out, and certainly for the last ten or fifteen years were very good friends, There was never any deep-seated quarrels but sometimes the situation was just a little bit on edge.
Weiner:At the same time none of you had a secure position there, because, as far as I know, the ICI money was supporting Simon, was supporting you, and I assume was supporting Mendelsohn as well.
Kurti:And Kuhn, though Kuhn was in a separate group.
Weiner:Did you have any proper university appointment at that time, any of you?
Kurti:No, Well, Simon did when Eggerton left Oxford in 1936, and an established university position, a readership in thermodynamics, became vacant, and Simon became reader in thermodynamics. And so he became a proper full member of the university. As far as Mendelsohn and I were concerned, we had no university positions. We were not members of the university. Mendelsohn had connection with Wadham College because when he came to England in 1933, both Lindemann and Keeley (who was Lindemann's second-in-command at the Laboratory) were members of Wadham College and they arranged for Mendelsohn to become a member of the Senior Common Room of Wadham so he had an association with a College though not a formal association with the university. I had no university appointment at all, I just had this research position in the Clarendon Laboratory.
Weiner:Which meant that your salary was paid through ICI sources and that you had no teaching responsibilities?
Kurti:I had no teaching responsibilities. I had in fact no responsibility at all within the university.
Weiner:How did this strike you? Were you attempting to find another position during the period? We know that Simon was trying to find another position prior to this time, and even later when he wasn't too sure of the security at the university or of the political situation, Did you from '33 on try to make any attempts to get a position elsewhere?
Kurti:No, I didn't, and the main reason for this was that I was extremely happy working with Simon and devoting all my time to research, And I was not married, I had no family responsibilities either in England or in Hungary, and therefore I said, I will stick to this job even though it is not formally secure — but I pretty well knew that as long as Simon stayed there and as long as he was interested in my working with him, somehow or other he would find something for me, And therefore I never tried to get some permanent appointment, either in Oxford or — at least in Oxford there was no possibility, of course,
Weiner:Occasionally there were openings — very rarely and with very high competition — elsewhere, but you didn't compete, did you?
Kurti:No, But as you probably know, Simon did apply for the Birmingham chair — but Oliphant got it. It was quite understandable and I don't think Simon was unduly upset. He thought he would apply, I think one of the reasons why he would have been very much interested in going to Birmingham was that he would have been in the same place as Peierls, and it would have been very stimulating to have Peierls actually in the same place, But he was not unduly worried about Oliphant getting the chair.
Weiner:What about the stipend itself? Was it adequate or was it just on a subsistence level?
The stipend was adequate, When I got there I got 250 pounds a year which was quite reasonable. I was a bachelor so I lived reasonably well on it, And that money increased two years later or three years later to 300 pounds, but that came about in the following way: As I said earlier we had in Oxford only a very, very poor electromagnet.
Soon we got some money to buy or rather to construct - a somewhat better electromagnet, but even that did not give us fields big enough for the sort of work we wanted to do with magnetic cooling, It was rather amusing that even the second magnet only gave us a field up to I think about 12 or 18 kilogauss if we used a very slim apparatus, so that you could approach the pole pieces to within about 30 millimeters from each other even that magnet was not a watercooled magnet. The magnetizing coils relied entirely on free convection from the outside air to cool them, and therefore what happened was that if you wanted to use very strong fields, we could only maintain them for 10 or 15 or 20 minutes until finally the windings got too hot, In fact, Simon suggested that we should calibrate our magnetic field, not in current but in small units, because the hotter the coils got the stronger the smell of the slightly burning insulation got.
Anyway, we decided that we wanted to do some experiments with a much higher field and those were only available in Paris at the famous Laboratoire du Grand Electroaimant at Bellevue, near Paris, Simon wrote to the director of the Laboratory, Professor Cotton, who was really responsible for the construction of the big Paris electromagnet, the biggest and most versatile magnet in exis tence in those days, and asked him whether we could come over and do experiments in this big electromagnet.
Weiner:Weren't there any others available in England that you could have used?
Not of the type where an apparatus could have been readily transported to and used for our experiments. There was one fairly big magnet, I believe, in Bristol, but the field wouldn't have been all that bigger than the field we had in Oxford, And the Paris magnet was ideally suited for our work, You see what we decided to do was that we knew that they were going to have liquid hydrogen available in Paris liquid hydrogen made in a then new liquefier in the French company, Air Liquide so we knew we would have liquid hydrogen, Now the method we used in those days for producing liquid helium was the so-called Simon expansion method which relied on the fact that if you compress helium to a pressure of about 100 or 150 atmospheres and cool it to the temperature of liquid hydrogen or preferably of solid hydrogen cool it down to about 10 or 11 degrees Kelvin - and if you then simply release the pressure on this helium, then the helium will cool and in the high pressure container - you need a thick-walled container to maintain helium at 150 atmospheres the helium will partially liquefy and you end up with probably 10, 20 or 30 cubic centimeters of liquid helium.
It was very well insulated because it was surrounded by liquid hydrogen, so it was enough for experiments lasting many hours, sometimes more hours than I liked, Sometimes it was enough to last for 24 hours at a stretch. So therefore we decided to take over the complete apparatus which had attached to it the apparatus for the adiabatic demagnetization take it over to Paris, set it up on a bench with all its associated vacuum system, and then this bench could be moved in between the pole pieces of the big electromagnet, and then when we wanted to demagnetize, moved out again.
You could do it with the Paris magnet because for instance the pole pieces could be separated - you could walk between the pole pieces and you could build rails so that the apparatus could move on rails and move in between the pole pieces, In this way you could carry out these experiments and do adiabatic demagnetization in fields up to 30 or 40 kilogauss. So it was all decided that we should go over the first visit was, I think, in the summer of 1935 and we built an apparatus. Finally, I remember in early August 1935 Simon and I packed all the bits and pieces into his very old car, an Essex Super Six, and took it over to Paris.
Simon then went, I think, visiting at other places, maybe he had a family holiday while Rollin, whom I mentioned before and who came with us, and I and one of the people in the Bellevue Laboratory, Paul Laine, who was one of the permanent staff of the Bellevue laboratory and also associated with this work, set up the apparatus on this bench which moved on wheels and on those rails, Finally, early in September, we got pretty well ready for the first experiments. There were endless difficulties, The hydrogen liquefier didn't work very well and after several tries we finally got some hydrogen. And then we had some difficulties with our own apparatus, We once managed to get liquid helium but it didn't last very long. So, in fact, the first visit showed us what the snags were, what the difficulties were, but we didn't get any results,
Weiner:How long was that?
We stayed there about six weeks, six or seven weeks or I stayed there, Simon only stayed about two or three weeks, But then we went back to Oxford and on the basis of this experience we redesigned the apparatus and we knew exactly what we could do in Bellevue and what we couldn't, The next visit I think was in the following April, April 1936. Then everything worked all right and we did for one month a series of very good experiments. Now you remember I started to tell you this story when you asked me what my salary was and I said it was increased from 250 to 300 pounds, It was very interesting.
Here I was and here was Simon, going over to Paris to do experiments, Today no one in his senses would dream of doing such a thing without getting a grant for it, But to get a grant for it in those days was out of the question. If you wanted to do something to advance your scientific reputation or to do an interesting scientific experiment, you just paid for it out of your own pocket. So I had to pay out of my own pocket the fare to Paris (not on the first visit, because I went by car) and my accommodations, my subsistence, in Paris. It was not very much. I was looking through my old account books and I found that the cost of four weeks in Paris — hotel, food, and so on — came to about, I should say, 20 pounds. It was still about 8% of my annual salary. But anyway, partly because of that, Simon arranged for my salary to be increased from 250 to 300 pounds. It was perfectly adequate and I lived reasonably well, quite well.
Weiner:Let me ask about the work in April of 1936, This was the first production of liquid helium in France?
Kurti:Yes, and in fact Simon and I were the first to produce liquid helium in France and also to produce these very low temperatures in France in the Bellevue laboratory.
Weiner:What was the relationship, if any, that you had to the French scientific community?
It was very good indeed, But, first of all, in those days there were not many people interested in really low temperatures in France, and so there was no question of our being regarded as rivals or competitors. In fact, they were very pleased that to some extent we encouraged in many ways interest in low temperatures. And I frankly was so busy keeping these experiments going — once we got it going we paid another four or five visits, each of one month duration. And they were pretty hectic periods, because the normal method of working was as follows: assuming that we did an experiment on, let us say, Tuesday, that means I turned up there about 8:00 in the morning and we left about 4:00 or 5:00 in the next morning.
So then I went back to my hotel in the center of Paris, I slept until the next morning about 11:00, then I got up and went to Bellevue and spent all afternoon and early evening, possibly until 8:00 or 9:00, to get experiments for the next day prepared. Then I went back to my hotel, slept, next morning got my train at 7:00, was there at 8:00 to get ready for the next day's experiment. So, apart from the occasional Sunday or Saturday, there was not much time. Now, Simon was always present during the experiments, He very often came out also during the preparation, but he had quite a lot of chance for meeting the Paris community. He was a regular attender at the famous Monday afternoon teas at Jean Perrin's laboratory in the Department of Physical Chemistry. It was a great occasion because that is where you met all the French scientists — they all worked near the Sorbonne — College de France, Ecole Normale Superieure and Rue Pierre Curie — and you met not just the physical chemists but all the others turned up at the Perrin teas.
Weiner:You wouldn't meet the group associated with De Brogue and other people from different —
Kurti:I don't think De Broglie really had a group when this happened, but I think many of the experimentalists were there. And it was rather amusing that although this was a very formal occasion — it became a tradition — they never bothered to buy tea cups and never bothered to buy spoons. Everything was done in laboratory equipment. You drank your tea — very often not out of beakers but out of (what are the conical beakers?) [Erlenmeyer flasks] — and you never stirred with a spoon. You stirred with a glass stirring rod. And Simon always jokingly remarked, "Of course, the main object of these Monday afternoon teas was to enable Perrin to kiss the largest number of female staff or colleagues possible." Because he would go around and shake hands with all the men and with tremendous kissing going on between Perrin and all the ladies present.
Weiner:Many of them were related anyway.
Kurti:Oh yes, This whole coterie in the Rue Pierre-Curie were - it was in those days said that the only way you could get a chair in Paris was to marry a daughter or a sister of one of the professors. I remember in the late thirties it was Michel Magat, who is a physical chemist — I knew him quite well from Berlin because he worked at the same time as I did, he did his D. Phil. thesis at the same time as I did - he worked on the explosion method for determining hydrogen specific heats with Kurt Wohl and he then went over to Paris and I saw quite a lot of him, And he used to say rather wistfully, "Well, it seems there is only one lady left who can still lead us to a chair." and that was Mlle. Hadamard, the daughter of the great mathematician.
Weiner:What was his name —- Henri or Pierre?
Kurti:Probably Henri Hadamard, a great mathematician, who was professor at Ecole Polytechnique.
Weiner:The one who wrote a treatise on creativity as well.
Kurti:Well, anyway, Mlle. Hadamard was the only road to a chair. Since then things have changed enormously. But in those days it was true there was a lot of nepotism in Paris.
Weiner:Did you have an opportunity to visit the laboratory of Irene and Frdric Joliot?
Kurti:No, The trouble was that I was so taken up in those days with the actual work at the Bellevue Laboratory because we wanted to cram as much as possible into these short visits. We could not afford the time — also, the magnet was also in demand and we couldn't use it continuously. There were lots of other groups working on it.
Weiner:What were they using it for?
The man who was one of the most senior people was Pierre Jacquinot who is now director of the Laboratoire Aime'-Cotton which was moved from Bellevue to the Orsay campus. They used it mainly for the Zeeman effect and spectroscopy studies and there was quite a lot of work going on on magnetic birefringence, the Cotton-Mouton effect, and some susceptibility work. This created certain difficulties — the fact that you had to share the magnet. For instance, we had to set up our apparatus a few meters away from the magnet while some other group was doing experiments with the magnet.
There was a rather amusing thing which happened on one occasion I recall. Jacquinot was adjusting his apparatus, was standing between the pole pieces and his apparatus was hanging there, and I didn't realize that the magnet was on. I didn't notice that the red light was shining. The magnet was not at a very high strength but it was on. Anyway, I was taking a small 5 liter flask of liquid air past the magnet — it was a metal liquid air flask made of iron — and while I was passing I suddenly felt some irresistible force slowly start lifting my flask. I wondered what was happening. And the next moment this force placed this metal flask against Jacquinot's backside.
He was standing at the apparatus and suddenly he felt something pressing him against the pole pieces of the magnet. It was my metal flask which was attracted by the magnet, and there was Jacquinot pinned against the pole pieces. I was standing there like an idiot holding the flask. I don't think I needed to hold it. And so then I shouted, "Turn off the current, Coupez le courant, Coupez le courant," and Lainé who heard this shouting, he came running along and went up to the control desk, the control console — they had a very good system whereby they could turn off the current very rapidly by giving counter- excitation to the generator — so he pressed the button for the counter- excitation instead of just turning down the rheostat. Unfortunately he mistook the button and instead of getting counterexcitation he got full excitation.
So the next moment with a tremendous jerk the magnet ran up to the full power and it took, I think, over a minute before we could extract Jacquinot from his rather precarious situation. These sorts of things happened. It showed that there are certain things which make working on an apparatus used by other people a little bit more taxing. Simply, I did not have much time to pay attention to other things. I still went occasionally to colloquia and I met a number of people. In fact, I established most of my friendships with French scientists during those three or four years. Many of the people whom I met after the war were the people I had known during these years,
Weiner:You were there during the period of excitement in the discovery of artificial radioactivity which was a completely unrelated field, Did you see that development in radioactivity and the new relation to nuclear physics as being any kind of a subject of special interest or focus or was it just another development in the French scientific scene?
Kurti:I don't exactly understand what you mean, It certainly gave a tremendous rise to French physics— it lifted up French physics— with Joliot Curie and Halban and the others. I regarded it as almost a rebirth or a livening-up of French physics because that rue Pierre-Curie school had become very important, and the other laboratories was Joliot-Curie at the College de France then?
Weiner:That was about '37.
Kurti:Was he in rue Pierre-Curie or was he at that time —
Weiner:At the Sorbonne, I think.*
Kurti:Anyway, it had a particular interest to Simon and me because it was in those years in the late thirties that the foundations were laid of our later postwar work in nuclear orientation, As you probably know, in those days Halban, who was of Austrian origin, lived in Paris and worked with Joliot-Curie, Halban knew Simon quite well, He would come out, I remember, every now and then to Bellevue and in late evenings during the experiments there were sometimes a half an hour or an hour when there was really nothing much to do but wait, And it was during a few of those visits by Halban to Bellevue I remember we had some strange furniture, some garden seats made not of straw but wicker and Simon would sit in one garden chair and Halban in the other one, I usually sat down for a short time on a stool and then dashed to and fro, And it was there that we really started discussing to what extent using these low temperatures and high magnetic fields, one might be able to orientate nuclei and what sort of experiments could be done with orientated nuclei. In fact all that work afterwards which led to the study of directional effects in radioactivity by means of orientated nuclei these ideas were born during those occasional midnight sessions of Halban, Simon and me sitting there in the Bellevue Laboratory.
Weiner:Let me ask one other question about the French scene, You mentioned that in the initial period there was no grant. Did a grant come through later on for that work for the visits to France and the expenses connected with it?
Kurti:We really never had any grants. I never claimed any expenses, I always and Simon the same paid for ourselves, And the apparatus was simply built in the Clarendon Laboratory, Of course, the French contributed — they provided all the local assistance, they provided the magnet, We didn't have to pay anything for using the magnet, We didn't have to pay anything for getting liquid hydrogen from Aire Liquide, *(Joliot had a Sorbonne appointment but worked at the Radium) (Institute, rue Pierre-Curie, until about 1937. -ed.) That was really a beautiful piece of very intense international collaboration between the Clarendon Laboratory and the Bellevue Laboratory. Wiener: On a strictly informal basis.
Kurti:On an entirely informal basis, There were probably one or two letters exchanged between Cotton and Simon and that was all.
Weiner:How much time do you estimate you spent there from August 1935 until some time in 1938?
The total amount of time was about six months in about five or six visits. There was quite a lot that came up in this work, Because of the excellent magnetic facilities in Bellevue, we could really get fields of up to 40 kilogauss if we made the apparatus rather small, about three or four centimeters diameter, and we could still get 32 kilogauss with apparatus with a diameter of something like eight or ten centimeters — we could do careful experiments with large samples and it was really in these Bellevue visits that we did two or three of the most important pieces of prewar work in magnetic cooling.
One was the determination of the absolute temperature scale at these low temperatures. In the earlier experiments of both Leyden and us, when we determined the temperature, what we did was to measure the susceptibility and to extrapolate the susceptibility with the help of Curie's law and said this is the temperature based on the assumption of the validity of Curie's law, in the same way that you could say this is the temperature based on the validity of an ideal gas law where you pretty well know that the ideal gas law does not hold down to low temperatures. And therefore we realized that it was essential to determine the absolute Kelvin temperature scale in this low temperature range.
There is one very interesting thing about it. That absolute temperatures can be determined by purely thermodynamic measurements had been known ever since Kelvin for the last — what was it — hundred years. But all the textbooks say, "It is very simple, You do this, you do that, and you determine the absolute temperature — in principle," You don't do it in practice — you use the ideal gas. When it finally came to determining the absolute temperature scale by purely thermodynamic measurements, by application of the second law of thermodynamics to magnetic processes, suddenly everyone started scratching their heads. How are we going to do it? All right, here we have a practical problem, How are we going to solve it?
And it was very interesting — there were quite a number of suggestions of how to do it, It was not so straightforward bearing in mind that there were certain difficulties, We had to measure the susceptibility, you could not measure easily the susceptibility in a magnetic field, Finally we developed a method which enabled us by purely magnetic and thermal measurements to determine the absolute temperature scale and to relate it to the temperature scale derived from the susceptibility measured in "zero" field. We started this experiment in Oxford but we did some of the best determination in Paris. One of the problems and that brings in really our first connection with radioactivity was the problem of how to introduce heat homogeneously into a paramagnetic salt cooled to very low temperatures.
You see, in principle, if you want to determine the absolute temperature scale, you have to determine entropy changes and heat content changes, The entropy changes you determine by means of demagnetizing from various initial conditions, The heat content changes you must determine by, for instance, measuring the specific heat, To measure the specific heat you must introduce a known amount of heat into the substance and must determine the change in temperature, for which you use some arbitrary temperature scale, for instance a temperature scale derived from the susceptibility. But how to introduce heat at these low temperatures uniformly? The normal method of winding a little heater coil around the specimen doesn't work here, because at low temperatures these paramagnetic salts have such poor heat conductivity that the outside of the paramagnetic salt may get hot while the inside will remain cold, And therefore it was Simon's idea: why not make use of certain radiations which are transmitted through the substance almost completely, only a small fraction of it being absorbed and that uniformly?
And the obvious thing is gamma rays, because we know the gamma ray absorption is very low, probably only a few tenths of a percent per centimeter or less, and therefore the absorption is almost uniform throughout the specimen, Therefore, let us use gamma rays for heating. That produced quite a few little difficulties, For instance, where do we get our gamma rays? Those were the days before you had artificial radioactivity, before you had cobalt or silver or any of the material, It was in the thirties, There was no artificial radioactivity.
Weiner:Well, from '34 you had artificially induced radioactivity.
Kurti:Yes, but you could not produce in large quantities artificially radioactive substances.
Weiner:Unless you had a cyclotron.
That's right, and even then, not in the quantities that we needed, And therefore, what we did was to use radon, radium emanation which has a half life of days, as a gamma ray source, Where did we get our radon from? Lindemann heard in the 1930's that the Czechoslovak embassy in London had in its safe a few grams of radium from their Joachimsthal mines, refined radium, which I think the Czechs exported to London in the hopes that they might be able to sell it. I believe Lindemann knew the then Czech Ambassador, Jan Nasaryk, quite well, or at least Lindemann had some contacts with the Czechoslovak embassy. And he told them, "Look, there you have this radium. It doesn't do you any good, and in fact, while you have it in your safe it gets less and less." Which was correct, mind you, though the loss is very small. "So why don't you lend it to us? We will make use of it, and we will pay for the insurance." I think we got about one or two grams of radium from them, and a radon dispensing apparatus was set up in what used to be the chemistry laboratory of Christ Church.
Christ Church, like one or two of the other Oxford colleges, had their own chemistry laboratory, although that was discontinued in the thirties, But it still had all the laboratory facilities, and that is where the radium was kept and that is where we collected from about 1936, at about weekly intervals, our little glass ampules filled with radon which then were put into a suitable lead capsule for radiation protection. If anyone engaged in radioactive work now would see the complete lack of precautions taken in the 1930's he would throw his arms up in horror. I remember, for instance, in the very first experiments when we just wanted to see whether radioactive heating worked, the little ampule of radon was sealed into a long glass tube, We had a lead capsule with a hole in it, i.e., a cylinder of about 10 cms diameter and 10 cms high, and we stuck the long glass tube with the radon ampule at the bottom of it into the lead capsule.
When we wanted to do measurements, I or Simon would go up to this lead capsule, remove this glass tube which was probably about half a meter long, take it out without any protection whatsoever — we tried to keep it at arm's length from our body — and then moved it near the apparatus and timed it with a stop watch, kept it in that position for whatever it was, 10, 20 or 30 seconds, moved it back, and put it back in the lead capsule, Afterwards we improved this a little bit and had a proper arrangement, but by today's standards it was just fantastic, The arrangements in Paris were just as slapdash since in Paris we used rather big samples, about four or five centimeter diameter, so that the absorption would not have been quite uniform, if we had irradiated it just from one side.
So we made a contraption, a kind of rotating gamma ray source, with a rotating platform and two uprights into which we could place the gamma ray sources, and they were located around the apparatus so that you get uniform irradiation from all sides. But there again the precautions were minute, We didn't build an enormous lead capsule around this, and yet the activities were fairly high. We used usually something of about the order of a half to one curie without any special protection, but fortunately afterward we didn't come to any harm. As a result of this technique of radioactive heating and we had to calibrate it, of course, but that was no great difficulty we managed to determine the absolute temperature scales for various substances and we could show that in some of these ex- periments we indeed reached temperatures of about two hundredths of a degree absolute, And perhaps the most interesting, exciting discovery we made there was a study of the behavior of some of these paramagnetic salts which, as I said earlier, behave as ideal paramagnetic salts even in the temperature range of liquid helium.
We studied their behavior when they are cooled to such a low temperature that the straightforward interaction between the individual magnetic diapoles becomes comparable with the energy of thermal agitation with k times t, and we found as expected that these paramagnetic salts at low enough temperatures exhibit behavior which could be either a ferromagnetic behavior or possibly an anti-ferromagnetic behavior, Anyway we showed that they have an enormous anomaly in the specific heat, they show hysteresis below these temperatures; then we showed that the susceptibility instead of increasing with falling temperature, actually turns around, passes through a maximum, and decreases with falling temperature.
We observed that first a few years earlier, in 1934 or '35, in Oxford, We did some experiments on manganous ammonium sulfate and in '35 (after we had started using gamma ray sources for introducing heat into the specimen) we found after that demagnetizing manganous ammonium sulfate, the susceptibility as expected, decreased as time went on, indicating an increase in the temperature of the specimen as we were to expect, And then after one demagnetization, we said, "Now let's see if we can accelerate the heating and by using gamma rays in addition to just heat flux from outside to warm the specimen," So we put on the gamma ray source and we measured the susceptibility, and lo and behold, the moment we put on the gamma ray source, the susceptibility, instead of continuing to decrease at an accelerated rate as you would expect, increased, The explanation for this is very simple. It seems that on demagnetizing the substance we reached a temperature which was well below this curie or Neel point, well below the temperature of the susceptibility maximum.
Now, if we allowed just the heating flux from outside to warm the specimen, then what happened was that because the specimen had a hopelessly bad heat conductivity, all that happened was that the outside got very warm and the inside remained cold, In fact, the outside very rapidly warmed, at above the temperature of the maximum, But the moment we started heating the substance as a whole, then the inside got also warm, and when the bulk warmed up its susceptibility increased because the bulk was still under the susceptibility maximum, And this is really how we discovered this thing. I remember Simon saying, "Ah ha, interesting, The temperature drops as we apply heat a nice contradiction to the second law of thermodynamics."
Weiner:That part of it was primarily done in Oxford?
The first experiments were done in Oxford and then later they were repeated in Paris, Let me just quickly tell you about one rather thrilling experience I had when Simon was asked to give a lecture at the Royal Institution — a Friday evening discourse and he decided, All right, I'm going to liquefy helium at the Royal Institution and show them experiments. It was really a most ambitious undertaking. Heinz London and I helped him, Two expansion liquefiers were taken up to London, just in case one of them gave us trouble, And we were proposing to do two sets of experiments, one to show superconductivity and the second one to demonstrate in a lecture theatre adiabatic demagnetization and show temperatures well below one degree. And that would have been only the second occasion in which helium was demonstrated at the Royal Institution.
The previous one was when MacClennan did a demonstration of superconductivity with helium having been brought over by airplane from Leyden. That was a beautiful thing, They in Leyden put a lead sphere into liquid helium, started a persistent current in it in Leyden, it was brought over by air to London to the Royal Institution, and MacClennan demonstrated that the current that earlier that day, in the morning, was started in Leyden, was still running.
Weiner:Do you know when this was?
Kurti:I can look it up. I think it was in 1931 or 1932, and the apparatus is still there which was brought over - I don't remember the name of the friend (he was an amateur pilot) who brought it over — but it is all described in the Proceedings of the Royal Institution.
Weiner:Those lectures are now published.
Yes, they are in the in the early l930's. So Simon said, "All right, we are going to liquefy helium there," I remember we took up a fantastic lot of apparatus. The back of his entire car was filled with apparatus and it took us several days to set up the apparatus. Everything was set, I was mainly responsible for all the cryogenics and Heinz London set up a magnetic thermometer, That was maybe the first case where a direct reading magnetic thermometer was constructed.
Previously we all simply measured the magnetic susceptibility by means of the ballistic galvanometer, but that doesn't lend itself to direct display. And so Heinz London set up an apparatus where the natural inductance was measured by an AC method and therefore could be displayed after amplification on a galvanometer. I was wrong when I said before that this was the first instance because I believe in the experiments of Giaque they also used an AC method for determining the susceptibility. Anyway, we started the demonstration and everything worked very nicely. First of all, we liquefied —- actually before the audience —- helium, Everything was prepared previously.
The helium bomb was filled with compressed helium, and by the time the lecture began all you had to do is to expand the helium and the temperature dropped, By the way, it was very wise that we took two apparatuses over be cause one of them got blocked just a few hours before the lecture and we couldn't use it, but at least we had the other one, So everything worked very nicely. Simon talked first generally about low temperatures, and then we came to the liquefaction of helium, It worked like a charm, You could see the temperature dropping on the dial of a gas thermometer and then he said, "All right, now, we are going to produce a persistent current in a lead ring attached to the liquid helium container, At present there is no current, as seen by the fact that a magnet needle amounted on a horizontal axis was unaffected, But we can produce a persistent current by first of all putting a magnet coil round the apparatus, which can produce a field which is bigger than necessary to destroy the super conductivity.
Any persistent current that is generated in this ring while the current in the coil is increased would be destroyed by the time the maximum field is reached. When we now reduce the magnetic field to zero, and take the magnet coil away, then there will be a persistent current left." And, sure enough, there was a persistent current, The magnet needle was brought up and instead of lining up with the earth's magnetic field it pointed firmly against the apparatus, You could see, in fact, by flipping it, that there was a very strong magnetic force, the period of the vibrations was short, And then Simon started talking about magnetic cooling.
In the meantime I prepared the thing for the adiabatic demagnetization to get the salt cold. It worked very nicely and Simon said, "And now we are - and I noticed, looking at London, he was sitting on the other side of the lecture bench, that he had started to pull at various contacts on his electrical circuit and had a more and more worried look on his face — and I knew what was happening, I knew that something went wrong with his electrical set-up. And he suddenly went up to Simon and whispered something into his ear, and Simon said, "That's all right," and London went back to his place. I was amazed that Simon took it so calmly.
I knew what London told him, that while we could do the demagnetization experiment we couldn't show anything because the thermometer was not working. Anyway, Simon went on lecturing and then suddenly said, "Now we are going to show you this experiment," London looked up and said, "We can't do it! It won't work," "Ah, I see," said Simon, he had not even listened to London, And so he explained quickly that we were having some trouble with the thermometer and that he was sorry we couldn't show it now. "So we could either keep the liquid helium in the hope that the apparatus could be repaired in the next 15 to 30 minutes or evaporate now the liquid helium and show you how the superconducting current will die out," The audience voted for the 2nd alternative and we showed with the magnet needle that when the temperature reached 7 K the superconducting current died out,the magnet needle flipped into its normal direction.
It was quite impossible and the audience loved it, And then when the whole lecture was over, I suddenly realized that the way I did the experiment was such that although the liquid helium in the main helium container had gone and the main helium container was at the temperature of liquid hydrogen, the small helium container which surrounded the paramagnetic salt was still at one degree Kelvin, So I told London, "Now, look, do you think you can find the fault ?" We really went to work and he finally found what was wrong where the trouble was and after about half an hour, he mended it, Now the question was how to get hold of Simon, who by that time was drinking whiskey in, I think, Sir William Bragg's (the Director of the Royal Institution) flat— to explain the situation to him before calling in the audience— a lot of people were still in the anterooms drinking coffee, "Look, we can do the experiment," They somehow got wind of what was happening, streamed back into the theatre which, by the time Simon was dragged in, was about one—third full. So we told Simon in a few words what had happened, the adiabatic demagnetization was performed and it worked very nicely.
Weiner:That's very good. It seems to me that low temperature work was dramatic and a curiosity because of the very dramatic effects you could produce and also because it is large scale enough in terms of its apparatus to demonstrate it.
Weiner:During this period there was work developing in the Mond Laboratory, or what became the Mond Laboratory, What was the impact of this? Was there a feeling, first of all, of competition?
No, not at all, In fact, it was again very interesting, They started, for instance, in l935-l936 also experiments using magnetic cooling, and we had very, very friendly collaboration with them, There was no feeling at all of rivalry or fierce cutthroat competition.
Somehow or other in those days the whole low temperature community, I felt, was first of all fairly closely knit they knew each other and somehow well, there was always a little bit of competition but it was never of an unpleasant nature, Certainly one of the most stimulating experiences was the great 1936 meeting of the International Institute of Refrigeration at the Hague. You know the International Institute of Refrigeration was founded actually by Kammerlingh Onnes in the early part of the twentieth century and embraced pretty well all aspects of low temperatures from the very highest low temperatures of ordinary domestic refrigeration or preservation of food down to the temperature of liquid helium.
The Commission One was a commission which had as its oblect low temperature physics, And certainly that meeting in 1936 contained a large number of very important papers on purely low temperature physics going down to tenths of a degree absolute. But so far I have only talked about one aspect of the work that Simon and I were doing in the Clarendon, Again referring to the temperature range obtained in magnetic cooling, we then started to do quite a number of other experiments, partly in order to study properties of liquid helium, for instance, and also topics such as thermal contacts and thermal relaxation at these very low temperatures. Now, by that time it was discovered that liquid helium is a superfluid. Also by 1934-35 it became known, thanks to the experiments of Rollin and Simon, that if you have a container with liquid helium below its lambda point, that is below the temperature when it becomes superfluid, then for some reason or other it looked as if some mysterious heat influx took place into the container which held the superfluid.
Rollin and Simon did a lot of experiments and they definitely established that it's the film of liquid helium which covers the walls of the tube connecting the rest of the apparatus to the container of liquid helium — and it was not quite clear whether it was the high heat conductivity of this film or some process of evaporation that created this apparently very big heat influx. It was finally the experiments of Daunt and Mendelsohn done, I think, in late '37 or early '38 which demonstrated that the film of helium which moves continuously, so what happens is that if you have a container the liquid helium will move up the walls of the connections tube until it reaches a point where it evaporates.
So if the container is open to a pump, then the effect is an abnormally large helium evaporation which makes it appear as if there were a big heat influx, while if you close the container, then the helium vapour can't get out so it recondenses into the container, again bringing heat into it. That was absolutely clear experimental proof although the experiments of Rollin and Simon finally led to a similar explanation. But they had no complete experimental proof whereas Mendelsohn actually showed that helium creeps up the wall of a beaker filled with liquid helium and goes over the brim to the outside and finally little drops form and the container can empty itself simply by means of this helium transfer.
We originally thought that it should be possible to do adiabatic demagnetization by simply putting a paramagnetic salt in a container filled with liquid helium then pump the helium after magnetization until it reaches a temperature of one degree, and then remove the magnetic field, Since the specific heat of helium is very small, when the magnetic field is removed the liquid helium will cool with the paramagnetic salt and its vapor pressure will become negligible and the only heat influx to this container will be along the rather thin-walled connecting tubes and that can be reduced very much, It never worked, it was only later that we understood that it did not work because of the helium film abnormal heating in this operation and that is why we gave up this method. But then we asked, how can we nevertheless study helium at these temperatures without abnormal heat influx? And we said, the only way to do it is to have a container in which there is enough helium gas so that after cooling there is a fair amount of liquid helium formed through condensation.
And a very simple calculation showed that meant making little high pressure containers which could accommodate helium at 150-200 atmospheres pressure and then seal it off at room temperature. In those days there was no simple technique for doing this, We started with a little thick-walled cylindrical container, open at one end, After having placed the salt specimen into it we had to put a lid on it which had to be hermetically sealed. Since it had to be leak-tight to superfluid liquid helium an ordinary compression seal wouldn't work and it had to be soldered.
It couldn't be soldered with ordinary tin solder because that becomes superconducting and would therefore mess up all magnetic measurements, so we had to use a solder which does not become superconducting, a metal which melts at a reasonably low temperature, so we used bismuth, I sweated for months before I learned how to solder with bismuth, It was very tricky. A thin filling tube which had been silver soldered to the lid was then connected to the helium cylinder, and then the container had to be filled with helium at 150 atmospheres, and then this connecting tube had to be sealed under 150 atmospheres pressure in a way that it was both pressure-tight, and tight to superfluid helium at 150 atmospheres. Well, it took some time but finally we worked out the method, And we did quite a number of interesting experiments, For instance, we showed indeed that the heat transfer is due to the movement of this film, and that the heat conduction of the film is negligible.
When we had two containers connected by a thin German silver tube with a paramagnetic salt at the bottom, a paramagnetic salt at the top, and liquid helium at the bottom of the lower container, we found that although round about one degree the heat contact between these two was very good because of the helium film, once we cooled it below about .6 or .5 degrees, heat contact was completely broken because although there was a film it didn't evaporate because the vapor pressure was zero and there was no heat conduction, And similarly, again using this technique Simon and I measured — the first experiment, I think, was in '38 — the thermal conductivity of liquid helium II below one degree and found that while it's very big down to about .7, it drops and finally becomes quite small.
Weiner:Was this done in parallel with some of the other work?
Kurti:We did it all in parallel. At that time we had a few more research students, but that was done in parallel. I think all this time that we worked with one, or at the most two adiabatic demagnetization apparatus. That was all, All the below one degree experiments were done on these.
Weiner:The paper on that, for example, is 1938, and so you are talking of work going on simultaneously with the Paris work?
Kurti:Oh, I'm sorry, you meant Paris. Yes, they were all parallel, and in fact, very often we did some of the work in Oxford, and then when we needed some high field work we went over to Paris.
Weiner:This is '38 and '39. There's a publication in '39 too. I notice that the Paris work was published primarily in the Comptes Rendus.
Kurti:Yes, we did it for two reasons. First of all, we owed it to the French that it should be published there. And secondly, it was fantastic how rapidly they published. The Comptes Rendus publication delay was one week to ten days. I think it's a little bit worse now, It's still only two or three weeks.
Weiner:Let me ask about the gamma ray work because I just glanced now at the bibliography. The first mention of it, I see, is a 1953 publication.
Kurti:That was nuclear orientation.
Weiner:I see, that was nuclear cooling so-called.
Kurti:But if you go back — no, nuclear cooling was '56 — but if you go back the first gamma ray work is, I think, in a paper by Simon in 1936 or '37. 'The use of gamma rays in low temperature calorimetry," I think.
Weiner:OK, let's see if I can find it. Well, we'll look that up in more detail later.
Kurti:If you'll show it to me I'm quite sure I can find it.
Weiner:At the bottom of this page is '35.
Kurti:Yes, here we are —- publication 1935. "Application of low temperature calorimetry to radioactive measurements." What he thought is because low temperature calorimetry can be made very sensitive, because thermal insulation at low temperature can be made extremely good, therefore he thought that certain radioactive effects could be very sensitively detected by low temperature calorimetry.
Weiner:I see, Let me say that I'll fill in a few gaps here.
Kurti:Time is getting on.
Weiner:The tape has a few minutes to run. Getting back to general questions about the Clarendon: were there colloquia involving the entire laboratory and other physicists from other parts of the University, or did you participate in any of them?
Kurti:Funny, I don't think we had real proper department colloquia, I just can't remember now, We had in Oxford a so called Mathematical and Physical Society, a very old established society which finally got defunct in, I think, the late 1940's or the early 1950's. That had occasional meetings. But perhaps the most important colloquium in Oxford in those days, which covered the whole field of physical chemistry and also a little bit of physics and chemistry, was a Monday afternoon colloquium or seminar organized by N. V. Sidgwick. And then there was a very active chemical society, the so-called Oxford University Alembic Club, which I believe is now defunct and they had some very good meetings. And there was an undergraduate physical society too in those days, which we don't have. It's silly, but I just can't remember whether we had a departmental colloquia or not, I rather have the feeling we did not, I will think about it again.
Weiner:Well, there are other ways of getting at it, too, But I was really leading up to the question of how much you were in touch with and keeping up with other areas of physics.
Kurti:We kept up definitely in the Clarendon by talking to all of our colleagues, because, as I said before, it covered very wide areas of physics, For instance, people like Szilard coming and doing artificial radioactivity work, Fritz London was there for some time, Schroedinger was, We really did keep in touch personally also with the rest of physics, But on the whole, I spent most of the time on low temperature physics and its various aspects.
Weiner:So in terms of Szilard and London and Schroedinger, and even when Einstein was there in the early period, you had very little contact with them?
Kurti:Einstein was there for only a very little while, Szilard was different because Szilard kept on going in and out of the lab, and Szilard I saw quite a lot, and Fritz London also, as long as he was there, But he left I think in '36 or '37, when he went to France.
Weiner:London went to the U.S.
Kurti:Yes, but he first went to France.
Weiner:It would be good to get some reactions on Szilard in terms of what you perceived of him as a person. Had you known him? After all, he was another Hungarian, Had you known him in Berlin?
Kurti:Yes, I knew him a little bit in Berlin. I saw a fair amount of him in Oxford, and, in fact, do you know Professor Miller who is now writing a biography?
Weiner:He came to the Varenna School. I met him there.
He came to Oxford and I told him a number of my reminiscences. One of the most amusing ones I might as well tell you. He was living in Oxford and his wife was in those days just his girlfriend. Dr. Trude Weiss was her name. She was very keen on taking Szilard on a little canoe trip on the Cherwell River. I told them that I had one of those little collapsible canoes which I kept in a little orchard on one of the branches of the river. So Miss Weiss was very keen. Could she borrow the canoe? I said, yes, certainly. So we arranged that on a Saturday afternoon I would show them the canoe and they could use it. Szilard was not very keen.
He didn't like this sort of outdoor sport. Anyway, we arrived at the place. It was a wonderful Saturday afternoon and there was the canoe, on the grass, under a few fruit trees. There was the river next to it and so Szilard first of all wanted to find out whether it was comfortable, So I put the cushions into the canoe and he sat down and wiggled a little bit and said, "Yes, it's quite comfortable," Miss Weiss brought a hamper with all the tea, Suddenly, Szilard said, "What's the point of putting this boat in the water? It's very pleasant here, The water is there through the trees, Why can't we have our picnic here?"
Weiner:Very good. I'm worried about the time on the tape. I would like for us to talk another few minutes if you have the time, Did you have the feeling even though he was moving in and out, was it understood that he was part of the Oxford scene or was he a transient figure?
Kurti:I think he was part of the Oxford scene, but not as much as Simon or Mendelsohn or me, But he did collaborate with and a few other people quite a lot and he travelled in those days always with his two suitcases, One suitcase contained his amplifier and the other suitcase contained his shaving kit and his pajamas. In fact, I remember at one time there was also some possibility of his being attached to a college in some very informal manner.
Weiner:Yes, I have correspondence with him and Lindemann on that.
Kurti:You saw the correspondence?
Weiner:Yes, I have copies of it.
Kurti:That was about the possibility of his going to Brasenose, wasn't it?
I don't remember but I got it from the Nuffield College Collection. Let me just summarize the things that we haven't talked about so that we can then consider what to do, Don't answer me now but I wanted to ask more about your recollections of Szilard and Schroedinger, for example. I wanted to talk about the relation to Lindemann and accounts of him as a person and as a leader of the Laboratory, including his fundraising efforts, I wanted to talk about the 1937 science museum show on low temperatures which I don't know anything about.
I wanted to talk about a very important subject the relation with colleagues in Germany during the whole period of the thirties - something which we know concerned many of the people who left, There's a lot on it in the Arms book (A Prophet in Two Countries: The Life of F, E. Simon, by Nancy Arms) and I've come across a lot of it in my own research. That's for that period. In addition to the line of scientific work which we haven't really followed, then the war, There are a lot of questions - personal ones, like the threat of internment that some people from Germany faced at that time the first war work at the Clarendon, I know that you with Arms designed a medical magnet, for example. And then the Peierls-Frisch report and the request regarding the isotope separation, and the development of the gaseous diffusion method how you got into that. Your December 1943 trip to the U.S. is all very interesting. The whole category then of post-war planning and changes, your expectations in terms of research, in terms of career, and security.
The work in the new Clarendon Laboratory. Then we pick up the research, the work on nuclear orientation at low temperatures, nuclear cooling, the achievement of this in '56, the effect of Simon's death in that same year; just how your own university position and responsibility developed; overall questions trying to take a look at the development of low temperature physics as a field of research from the thirties up to the present; and the whole question of changes in research support during the thirties. Now you've heard my agenda and it's on tape for the record, do you get the feeling of the fact that we have a great deal more to talk about and I hope that you will think that some of it is interesting?
Kurti:All right, and what I would also like to put on the record that even before the whole thing is transcribed I should like to have a transcript of your last few minutes of remarks so I would like to know what you would like to hear about.
We can do that easily. I can put that in a letter actually because I was reading from my outline and it's based on the preparation that I did for this, I said, well, I'm ready to talk with you about these things if we have the time.
Session I | Session II