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Interview of Clarence Zener by Lillian Hoddeson on 1981 April 1, Niels Bohr Library & Archives, American Institute of Physics, College Park, MD USA, www.aip.org/history-programs/niels-bohr-library/oral-histories/4996
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Brief account of family background and childhood; education: Stanford University from 1922; Munich spring and summer 1926 (Sommerfeld and Wentzel); Harvard University 1926. Main part of interview discusses publications and collaborators. War-related work at Watertown Arsenal 1942-1945; most to Institute for the Study of Metals, University of Chicago, to work on micro-mechanism of fractures. Ferromagnetism work starts 1950. Move to Westinghouse, comments on industrial laboratories (U.S. Steel, Bell Laboratories); move to Carnegie-Mellon 1968.
Okay, well, this is Lillian Hoddeson and I'm with Clarence Zener today it's April 1st, 1981 and we're sitting in a lovely office at Carnegie Melon University in Pittsburgh. Okay, well, let's see, you were born in the Midwest, in Indianapolis.
And we're interested in a little bit about your background, your parents, were they native Americans?
Yes. Okay, I think I will tell you that background that is pertinent that has influenced —
Your career. Great.
The peculiar aspect of my early years were conditioned by the fact that my father died just about when I was born, so my mother. I was a third child, she was … my father died of tuberculosis, so my mother was very afraid of her kids not catching any disease, so we were not sent to school. And as a matter of fact, my brother and sister (left to read) early with an aunt and I didn't take to that. So it wasn't until I was something like 9 or 10 that I learned to read. And we all three of us went to a local what was it A. and Donald school, not a public grade school part, high school. Now the reason why it was why it had an influence I think, was when I went to college, I guess I was about 16, I felt I had a great advantage over my classmates in that learning was new to me and here these guys you know had all been studying for 12 years. And they impressed me as being rather weary of study, and so I and as a consequence, I have always discouraged with our kids the standard school, but it's made us sensitive to the dangers of the dulling of the imagination which occurs so by the time our kids we've had five kids one has died, by the time they'd reached junior high school we practically yanked them out and sent them to a private school. Just because of the danger of getting bored. The other aspect of my early years was that I was a very bad stammerer, I don't know quite know when I got over that, but it wasn't until quite late in life. So this had an effect of being had an effect of discouraging working with other people. It rather forced me to be a loner. So that the aspects of my early life that have had an effect.
How about the influence that led you to choose science in your studies?
Yes, well I can be very specific there. We had a set of volumes which we called the Child's Book of Knowledge. I don't know if you have ever seen that, I don't think it exists now.
I had that too when I was little, a later version. It's wonderful. It was a mixture of fairy tales —
— and scientific information, experiments, wonderful facts, pictures of stones. I read that too.
I don't think there was anyone in my community, it was a small town, Vincennes, Indiana where I was … There was no one who had ever heard the word "physics". But from that somehow I felt that's what I wanted to do. So that's how my —
I didn't realize it went back that far, that was one of the great things in my childhood as well. I still have it.
That's interesting, that's very interesting. I remember a remark by my mother; she was worried could I ever make a living in my difficulty in communication. Well she thought well maybe forestry would be a good profession. So I came down hard on here I said, "No, I want to go into physics."
When did you make that decision? Do you remember about how old you were? 12, 13?
It must have been, yes about 12, 13, 14, in that period.
This was a period when telephone was beginning to become widespread, and radio.
Not radio, oh no. At least let me say I don't remember anything about radio before I went to college. This was a small backward community.
How did you choose to go to Stanford?
Well, this was interesting. Another event that really had the big effect upon my life was we took oh about a six week six month camping trip to the West. And probably a three months all summer and we wound up in Arizona at Tucson, that was a campus a good place to go to a college I guess we wound up there in the mid-year and so I went to the University of Arizona.
Arizona? I see.
All I can say is though Stanford had a good reputation it was easy in those days to get —
You heard about Stanford through Arizona and decided to transfer. And this is about 1922 or so.
Then you became a full-time student at Stanford and lived there and, what are some of the most important events that took place or were there some outstanding teachers or courses?
No, there was nothing. Webster was there and that's about, I can recall nothing no conversation no special contact no inspiration with him.
I gather you got your bachelor's in Mathematics.
How did that happen?
I have always disliked experimental work. It seemed to be a characteristic I hate to say hereditary but I have a daughter who started college in a local Chatham College, do you know of it?
I've heard of it, I don't know much about it.
And they had a laboratory and electrical course in chemistry, and her laboratory instructor couldn't believe that this was the same … who was getting such excellent excellent grades in electric. Um, so, I wanted to avoid the laboratory, so I majored in mathematics.
Were you aware of quantum mechanics happening at that time?
No, I was not aware.
I mean, there's no reason why you should have been in '26.
Just a moment now, I left I spent a summer in Munich after graduating from Stanford I think I left a quarter early and was did enroll in Munich so I attended the seminars of Sommerfeld and Wentzel.
So that must have been 1926 or so.
That's right, the summer of '26.
The summer of '26.
That was a big summer.
I see. So you heard about the excitement right from the —
Right from the horse's mouth.
I mean, it certainly was right where it was happening, in part. Now at this point you need to tell me how you happened to go to Munich. With your background, and coming from Stanford, with a mathematics degree. There must a story connected with that.
How did you know to go there?
It was part of the adventure.
How did you choose Munich?
That's difficult … in those days, there were musical comedies, and you know Bavaria was attractive.
Well, it's certainly a center of music. So you chose it for cultural reasons.
Music is not that attractive. That's a question I really don't know.
In other words, you did not have to with the great physics that was coming out of Munich. It had more to do with other aspects of Munich. How did you support yourself on that trip?
Well at that point when did you decide to go to graduate at Harvard in particular?
I had decided that before. I went —
While you were taking mathematics courses, you had decided.
But went in the physics department, not in mathematics. I was never —
Yes. I was never attracted by the formalism of mathematics. I've always regarded mathematics as a tool, and I had been able to use it respectively as a tool, but only as a tool. I have a granddaughter who graduated here several years ago, in the math department, and she did like pure mathematics, something like that I could never stand. So I would never have thought of anything in mathematics.
So you applied to Harvard sometime before going to Munich, while you were still at Stanford, do you remember who you applied to?
No, I didn't know who was there.
Why did you choose Harvard?
It had the reputation.
Yes. Once you got to Harvard then, I guess, it must have been the fall of '26.
'26, yes. I think that's right. There it was quite different, whereas in Stanford I really wasn't part of the department at all, although I took courses, at Harvard I sure did get to know people. And they had an influence upon me.
Well, who were some of these people who were particularly important?
Well, when I look back at Harvard, in my years at Harvard, I think of and there is no doubt that Bridgeman had a profound effect upon me.
In what way?
Well, when I was at Stanford, I took a course in thermodynamics, and the guy that taught it was sort of mystified and he imparted that impression to us, of mysticism to his students. I never will forget Bridgeman pacing back and forth, on the ground, you know, expounding thermodynamics, and he had this system in giving courses of writing his problems on cards which he would pin around the room. And before the term was over, you had to solve all of those problems, and they were very good problems, you know, they were problems that made you think, and as a consequence of his course on thermodynamics, I've always love this subject and I it's become a part of me, so to speak. This had had a great influence on the subjects that I investigated. So, in another sense, I had a slight contact with Oppenheimer. And he had a profound on me in quite another way.
Who? Oppenheimer was at Harvard at that time?
No, he had been a student at Harvard. And I was only with him one day and he was on a trip through. And the influence he had was the following.
This was during your period at Harvard?
This was it must have been I returned to Harvard for about a half a year on a National Research Fellowship, so this wasn't in my … year.
So this was a few years later. But tell me the story.
But the effect that he had I recognized here's a guy that does things that I could never possibly do. And I recognized that other people could do things that I can't do, which I think was healthy, to recognized one's own limitations because I have seen people that have tried to work out of their depth and I didn't succumb to that.
And you learned that from Oppenheimer.
Let me say not that Oppenheimer himself was a very gracious person he wouldn't he would be the last person to want to give this impression, but my God I mean he could read very quickly … books, and he knew several languages, including Hindu, my gosh, just incredible to me, a person of his capabilities.
Who were some of the other people at Harvard who were important in that period?
Well, I felt since I had left Harvard, I've been very grateful to Campbell.
Campbell. Wasn't he teaching quantum mechanics at that time?
Yes. But he helped me tremendously in that he recognized that I disliked course work. And what he did was have me come in to his office a couple of hours a week and give me problems to work so this is really how I primarily graduated from Harvard was working with Campbell. He would give me a problem that he was interested in and I think he had a struggle with the faculty because I didn't take the standard …
Courses, and particularly had a difficulty because I knew nothing about the laboratory work. So I have always been very well maybe I suffered, I don't think you profit from something you don't like.
Was Van Vleck around?
NO, Van Vleck was not around, he had left.
And Slater was there in my last year, he had been in Europe my first two years.
But then you overlapped slightly. Was there any interactions there to speak of?
Not really, not. I mean I took a course from him but there was not any interaction, no. Slater was rather like I was, a loner.
Right. According to Slater's writings, in his view, Harvard was the best place to be in the country at that time for learning theoretical physics.
Do you agree?
Well, let me see, if you had taken Bridgeman away — now, Bridgeman wouldn't, you wouldn't classify him as a theoretical physicist.
But he sure, no one could fool him, and he knew nothing, well I don't know. I certainly did not use quantum mechanics. But I don't think Harvard grew as rapidly in theoretical physics as other places did, but at that time I really don't know who was at other top places.
Were you in touch with the research literature through your work at Campbell, for example the (???) was very important.
Oh sure. This was the —
And I guess (???) was important as well.
Important, but —
Not as much as the (???). And of course you were aware of the, well, I guess, when did you become aware of the quantum theory of solids was just being developed in that period.
Of course it wasn't called that then.
It was called electron theory.
Well, I guess it was not until I went to Bristol that I got involved in the mainstream and that was interesting in that I was just looking up my old work, and the first work I did in the electron theory were the properties of free electrons in the gas in the atmosphere.
I see, which paper are you referring to now?
Um, let me see.
First you worked on hydrogen ions with Gilman.
Yes, this was in 1933 in (???).
Okay, we're all almost up to that, but I was just wondering whether we could just very quickly talk about the earlier period, not in detail. That's just to set the background; at Harvard you worked with Gilman?
Yes, Gilman was a post-doctoral fellow.
I see. You worked on ions and molecules.
But first I would like to speak about one paper.
Yes, which one is that now?
Low velocity in elastic collisions.
You must have done that when you were at Princeton.
As a matter of fact I was at Cal Tech.
You were at Cal Tech then. Oh, I see. In 1929 you went to Germany for a year.
Yes, a year, yes. A Schilman fellow. And then I got a National Research Fellowship.
And what did you do?
First at Harvard, and then at Berkeley and then Cal Tech.
It said Princeton.
So Berkeley, Cal Tech, first Harvard, Berkeley, Cal Tech, and then Princeton, I see. Now, the paper you'd like to speak on you wrote at Cal Tech.
Yes. Now, I had been interested previously in collisions in molecular transfer of energy to vibrational and rotational energy. And I recognized that those of us working in collision theory in mechanics could have done a much better job of using classical physics for the part of the system. Are you familiar with what was then known as the Born-Oppenheimer?
The Born-Oppenheimer approximation, yes.
If you go a little bit further than the Born-Oppenheimer approximation, and treat the atoms themselves, that is, purely classical, and confine your quantum mechanics to the electrons, then the formulation of what we had been doing comes out in a very simple form that has been given the name adiabatic behavior. I have to go to the board here. If you have two energy electrons and here … of an … and you're in one state, and you move the position very slowly. You will stay in that state, that's the adiabatic approximation. Now, if this is the difference in energy as a function of position and therefore a function of time, and we ask are the probability of winding up in the other state, the transition probability after we've gone through all of this involves an integral of I wish to do this in classical mechanics. If we consider this as a frequency of vibration, that is, in quantum mechanics, we relate this to … frequency.
In quantum mechanics, if you have two coupled oscillators, and you start one of them vibrating and then vary the coupling between them, and then pull them apart and ask what is the probability that the energy has transferred from one to the other, one will get a … function … Well, if you I'm sorry … if you solve the classical problem, where rather than difference of energy you consider two frequencies, two normal modes of vibration and you vary the coupling, you have for the transition probability, you have an integral, ah, yes, which involves the product of two functions, one which is the coupling, the other is a function, so if you convert this into sines and cosines you have just a function times a purely a function ??? Now, the transition probability is a function of the of n, where n is the number of oscillations, at the half-width of this curve. If this coupling of functions has no discontinuity but all these … are continuous, this is a transcendental function. Meaning no matter how high, n cannot be expressed as a power of a function. It has the form minus a constant of the order of unity times so that the important physical consideration to compare the time of interaction with the number of oscillations in that time. If there are lots of oscillations, the probability of transition is very low. This corresponds to, let's say you have a pendulum and you push it very slowly and then return it. That concept is applicable to many, many situations in physics and once I recognized that, that's why I wanted to bring this paper out, and it was I wrote several papers and got into, and the first time I got into solid state.
Through the application of this concept.
You see, the next paper was the exchange of energy of monatomic gases and solid surfaces, and so someone had observed —
Do you remember where you did that?
I think that was at Princeton. Someone had observed that you get perfectly elastic, you can get perfectly elastic collisions of monatomic gases with a solid. …, you see, this is impossible. But then you recognize that as long as the time of collisions of the atoms in the solid, as long as the time of interaction is long compared to the Debye frequency, the probability of energy transfer is very low, so I think in most of these papers, I was stimulated by experimental work. I would see —
How to explain it.
To explain it in a quantitative, not just a qualitative way.
The experimental work that you were taking into account in these problems, work you had learned about through the literature or through discussions?
You know, this is a tough question to ask now. Now I see in I'm quoting a paper that came out in the Proceedings of the … Philosophical Society in 1932, so it had apparently just appeared, and I frankly don't remember how I got onto the literature. It's an interesting question, but in those days, I certainly spent a lot more time in the library than I do now.
At Princeton, were there some other people interested in these sorts of questions, or in fact the other places you stopped for a while, or were you working alone most of the time?
I was working alone; on the other hand —
I'm thinking now, was Wigner was important to you?
Wigner was there.
Did you talk with him a lot about these things?
In one of these papers I observe, I think … the discussions he was in but —
He was just beginning to get interested in solid state at that time. I don't know, did you overlap with Seitz, his first graduate student, who I think came in —
Seitz was there, yes.
You did overlap, it probably was just in your last year.
I think he was, we knew one another. I'm sorry this question as to how one, it's a very important question as to how one becomes aware of phenomena. I certainly am a person that likes to talk about … to colleagues so someone else might have seen this work and mentioned it. Then the next paper, the double Stern and Gerlach experiment, is a similar kind of a problem of application. So wherever there was an application, I just lapped it up.
Right. How did you decide to go to Bristol? Because your next series, I think, come out of Bristol, don't they?
Yes. That was because of the year in Europe on my Schilman fellowship, I spent the first part in Leipzig and then in Bristol and, let me check — I think in, I had passed through Bristol and had corresponded with Lenard Jones and somehow he offered me a two-year fellowship there.
And you decided to go there. That was the best place to go to do the kind of work that you were doing.
Yes, it was, and fortunately, I met Harry Jones. We had a profitable time, and my impression, I got a very strong impression of the way the English people work at least at that time.
I would be very interested in a comparison between the British group because you were at the three major centers for quantum solid state physics in that period, the Cambridge environment, Princeton, and Bristol, all practically in the same year. So you're in a good place to comment.
Well, I tell you, my impression was that in England when they finish a paper, they then they study and wait until they find something exciting whereas in contrast to my impression of the U.S. universities, where people always had to be doing work. They would worry before they finished one project, thought what they would do for the next, whereas in England my impression was and I sort of took up that flavor of being happy to have something off my chest and to study what was going on then until I ran across something that looked interesting. And to me that meant experimental work that needed interpretation. I spoke about a paper in (???) on the properties of free electrons.
Yes. That's really your first real solid state paper, the one that —
If you exclude the collisions —
That's on a transition between molecules and solids.
It was my first experience with solid state but it was on electrons in the atmosphere, see. Oh no, I'm sorry.
You said that this was a paper, I believe I have it here, where you —
Yes, that's right, there's the work of Woods, and a model of Kronig.
Yes, that's right, you see Kronig had interpreted Woods in terms of the band theory. That was a qualitative interpretation whereas my qualitative I mean he couldn't obtain agreement of numbers.
He showed that the alkali metals became very transparent in the ultraviolet region.
See prior work had interpreted the reflection of radio waves from the by the ionized atmosphere in terms of the properties of a free electron gas with collisions, but the mere fact that they were free to oscillate with the applied electric field endowed the gas with the property of having a critical frequency if you start at low frequency, a critical frequency beyond which the waves go through. And the same formula that they used in interpreting the transparency of the ionized layer to high frequency radio waves is exactly applicable to the alkali metals, so this is a case where I tried to make fun of people who are using modern quantum theory when classical theory does a better job. So this then got me onto the properties, those properties which (???) characteristic of quantum theory and cannot be expressed in terms of classical theory and Bloch had just done his work and joined forces with Harry Jones.
You refer to Kronig's work, quantum mechanical work in this paper. I wonder if you could comment on Kronig's role. He's someone who we probably won't have a chance to … don't know how major that was.
I had never met Kronig. And perhaps was prejudiced by this scientific exchange so to speak. So I can't, I just don't know, now let me say I did have occasion to meet several places. Who's the other Dutch?
Kramers. I got a lot from him, I just thought he was a tremendous guy. So I just can't.
Tell me more about Jones and the work you then you went to first on metallic conduction with him, the background of that would be very interesting, there is this Royal Society paper you wrote with him, '34, for example.
Yes, we wrote a couple of papers. I think we wrote.
Yes, I have two here, and there may be even more.
The, this was a fruitful collaboration that we had, and although we didn't do anything new that hadn't been done before I think we certainly systematized things, but the major effect was upon him and upon me. That is, because of this work he then went on on his own on developing the properties of his own cells. And I went on on the electrical breakdown which I wouldn't have done unless I had had that background. So I think it's main effect was tutorial for us.
Well, it also made somewhat more precise the work that Bloch and Peierls had done.
That's right. Well, incidentally, then I would like to skip a couple of years. You see in this work we were taking something that had been started by someone else, by Bloch and amplified it, and I did this for another year or more sort of felt that this was really no way to get ahead. And because of this being on the tail end of ideas when I did conceive of the idea of a mechanism of damping in metals, I seized upon this as a way of developing a completely new activity and that's why I really plunged into that.
How did you come to that, do you remember?
Yes, I remember very well. There was work at the Bell Telephone Laboratories where they examined a lot of materials and found what they did to the material this was Wiegel and Walters, that the material was sensitive to what they had done. Well, having worked in solids for several years, I was very puzzled as to what could be going on. And I will come back to this diagram here of transitions. It being the answer formally consisting of a product of two terms, an interaction term and a frequency term. And it, I was aware of the fact that the damping of sound waves that you have a frequency range where you go from high frequency to low frequency where you have a transition now the velocity of sound is given involves the specific heat. Now there are two specific heats which had been recognized as important. One where the time that you take to measure the specific heat is long compared to the time it takes to establish equilibrium between vibrational and rotational … freedom and when it's … that is if the sound waves if the frequency is so high that there is no time for equilibrium to be established between vibrational and rotational degrees of freedom, or vibrational and translational, then you have one specific heat, and so this recognizing this led to the concept that you will have a damping depending on whether you have whether you have the … you change into doing an oscillation is proportional to the heat flux.
You're now getting into a discussion of your papers on internal friction, is that right?
You asked me what led me, how I got the concept.
Of the thermoelectric internal friction.
Right, right, right, right. Okay, so, —
So if your frequency is so high that there's no time for an appreciable heat flux to flow you'll have zero generation of entropy if it's so high that there's no time to establish a temperature or if the frequency is so low that there's no time if the frequency is so low that you have thermal equilibrium your delta T is zero. So recognizing this essentially from Bridgeman's classes in thermodynamics that entropy is … flow of heat downhill, that came as a flash so to speak that this is (???) possible mechanism of damping in solids. So that was the first and only time I've done experimental work.
Let's talk about these papers. Though I'll want to come back to some of the ones we've skipped.
Okay, we'd better come back first.
Should we come back first? Okay, then we'll pick up again. We don't have to do it too thoroughly. The work that you did with Jones, I was wondering if we said everything that was important about that before going on. There's also a paper on electrical resistance, change of resistance in a magnetic field.
Yes, the Hall coefficient. Oh, that's right, yes. With Jones.
This is again in the category of improving the work of Bloch and Peierls, and we needn't spend time on that. There's also some work on optical properties with Mott. I was wondering if you consider that important or —
No, that was a review.
Did you work closely with Mott or was this just a freak joint project?
I guess you would classify it as a freak.
Did you spend much time talking to him, or was Jones here?
I had known Mott before, and was in Cambridge several months.
Right, and then you working on collisions and so was he. So there was a merging of interests. Well, how did you then get to work on the theory of electrical breakdown of solid dielectrics, which is perhaps your first major work.
This was stimulated from work at that time on the decay of nuclei and at that time they were working on the escape of the electrons and protons from the nuclei penetration and having worked on the band structure it was obvious then that the same phenomena was taking place there so this was a case of being aware of what was going on —
In other fields.
In other fields, yes.
I see. You referred to Von Hippel a paper he wrote in the (???) in '31 in which he proposed a model analogy to electrical breakdown in gases. Is this something you came across in the literature as well and then decided —
This I will classify as, you know I referred to this custom tradition in England when you finish a paper you read the literature thoroughly read the current literature, this is probably a consequence of that of going through the standard journals briefly. I think that was it.
You think the Gamow work is more important in your actual motivation in this paper.
Yes, oh yes, that was the motivation, that's right. But I was aware of the other interpretation because I had to not be ignorant of it.
You have a paper on magnetization …
Yes, that was just a —
— separating out of two phases in a homogeneous liquid.
Phase transformations had always, I've always often enjoyed that, because thermodynamics is related to it, statistical dynamics and thermodynamics are related.
You did some work on theories of the spectral selective … effect.
This was a case of again keeping up with the literature and observing that very anomalous … and this is a merely recognizing that the proper frequency the cross section of collisions of light with a classical oscillator isn't big enough to explain what was observed. This was where I was fishing around.
I notice again you probed into the earlier literature. … in the footnotes. Then you go into the Hall coefficient in alkali metals. By then you're in Washington University in Saint Louis. And maybe before talking about the paper, you could tell me a bit about how you happened to come back to, why you chose Washington and something of the environment there in contrast to where you had been working until then.
You probably aren't aware that in the '30s there was a Depression.
I don't why you should be. I had made the mistake obviously of not getting a job I had lived on scholarships before and Washington University was the first place that offered me a position, more than a scholarship and —
What kind of a place was it at that time?
Oh, it was a very —
Yes. The tone of the department was set by the head of the department, Arthur Hedins, who was really a tremendous guy. Have you met him?
No. What is his field?
Experimental physics, but in particular surfaces and this involves a very difficult experimental techniques to keep surfaces clean. Then I say he was a wonderful person as an individual and Arthur Compton had just left there, so Arthur Compton had helped built the place up, and it had a very fine spirit. Now it was very good for me, because I was expected to be the theoretical physicist there and as a consequence I did some work with Jauncy. Jauncy had worked with Arthur Compton and they had worked on the effect of temperature on the reflection of x-rays, and I saw an opportunity of doing a better job than they had done, so I worked with him, but this an example of trying to help the people with whom one associates.
The Hall coefficient —
The Hall coefficient, again I'm sure a paper came out that I saw could be interpreted, let's see, a paper had just come out giving some —
Experimental studies of Tutor and Williams.
So I had really just come back from England, so still had this habit of —
Reading the literature. There's a neat little letter on the uncertainty principle.
That's right, yes.
In which you get Heisenberg's results in just a few lines, that I enjoyed. Okay this paper on the temperature and reflection of x-rays we discussed, that's in two parts. We started to discuss that. Isotropic and anisotropic.
Really three parts here.
Oh, three parts, excuse me. Also allotropic crystals. Now Jauncy was he a member of the department?
Yes, he was the senior member next to Hughes.
Okay, I'm just wondering … told me about the background of those papers so I think we can move on to the theory of internal friction which you just gave me the background for. Now this is a major concern of yours for I don't know how this went on, the papers are they all 1937, no, one in '38, '37-'38, there are five papers in a series plus several others.
Now this I'm quite proud of.
Yes. Which is this now?
This is a book on
(???) Solids by Nowick and Erin.
Why I'm proud of it is they acknowledged that this was so to speak a I regard this as a culmination of —
The work you began when you wrote this monograph I have with me on elasticity and an elasticity of metals. Let's see the book that you just gave me was written in 1972, or published in 1972 anyway.
You see what has happened is that it turned out this was a very precise tool for measuring what's going on in solids. But you have to know what might be going on and then prepare your specimens so if you are examining is a major factor. And it turned out that thermoelastic internal friction is one of the larger components, so one has to design the experiment so that it is not operating if you study the other phenomena so I think this book includes the effect on metallurgy which has taken place using these concepts. For instance —
That's a very important subject that you wrote about later on, but we may as well talk about now since it came up, the tremendous change in metallurgy that came about, I suppose starting in the 1930s, when these —
Your paper starts in 1937, but I guess the impact took place later?
It wasn't after the war that we recognized the various phenomena that can take place, not until I —
Cyril Smith has written lots of articles on the theme of the metallurgists and the artists and the technology people forming a tradition a sensual, essential tradition that was really quite different from the more abstracting, model-building tradition of the physicists which didn't come together until quite late in civilization.
I tell you, you have brought Cyril Smith into the conversation, and you have also been fishing for the impact on people. Cyril Smith, well, at the time that we are talking about, I was desperate for financial aid, I had a wife and several kids, so I heard of a position in New York a city college, which was a terrible place as far as physics was concerned compared to Washington University, but I could have a 50% in salary which meant a tremendous amount, and I wanted to I had the concept of the microcrystalline thermal currents, so I wanted specimens to demonstrate what the theory predicted, so I went to the metallurgy department at Columbia University, and asked advice as to whom I should go to to prepare the specimens. And the head of the department told me that there's only one man in this country that would go through the trouble of helping you and he told me it was Cyril Smith. And a little later I was at a convention where Cyril Smith was at. So I took the opportunity of getting to know him and told him my problem and was delighted to help, which always impressed me that he would of course I gave him a good story but he was fascinated by what I told him so that established quite a friendship.
I have a friendship with him also that has grown out of discussions over the history of science.
Well, he's just a nut on history.
Yes, he's wonderful. I'm very fond of him. Well, let's see, there are five major papers in the (???) on internal friction in solids, one on, first you start out with the theory in … and then —
Incidentally, while you're speaking about that, this gives in this book an independent experiments from our experiments, no arbitrary constants, no adjustable constants for the theory. And there's no background subtracted, so you can see that under the right conditions, this is the dominant.
It's a beautiful curve.
It's incredible. Well, all right. I don't know if we want to go into the details of internal friction work, they're very clear in the article, I think we'll go back to them. I would be interested in the responses you got at that time to these articles. Were people did people recognize their importance at the time or did it take a while?
No, I would say there was very little response.
You wrote a note in (???) about this work.
This was a case people did experiments and got results which they didn't know how to interpret.
Was there anybody responding to this internal friction work at the time?
No one at all. Although it was important later. Then there's a paper you wrote with Herman Feshbach.
Oh yes, that's interesting, because I come back to this curve of adiabaticity (???). The transition probability between two states are the energy absorbed in a collision is a product of two effects. There's one is the area beneath the curve. And the other is this number n. And those two, the precise shape has some effect on a. In the collision of a ball with in the examples that we Feshbach and I worked with, the area underneath this curve corresponded to the impulse imparted to the system … which is a measurable. And from the elasticity theory we could get an estimate of the time of contact, so knowing the time of contact and the actual frequency we could obtain the energy imparted to what was the system we were considering? I think we were considering a mechanical system.
Two elastic bodies.
What date was this?
I have the paper, it was in '39. Would you like to see the paper? It's right here.
Oh yes. (tape ends) Once you normalize, let me speak now of we refer here to work of Raman. Here's that integral that I was speaking about.
Equation number 2.
Where you have a tiny … function times a function which … and this is the basic form —
Of the interaction system.
That determines whether it is adiabatic or part … So once one recognizes this general form then one is encouraged to try to do something. Now later I improved upon this in the next year I found a method of getting an exact solution to improve upon Raman's this was just before the war. The intrinsic inelasticity of large plates, (???). This was an extension of the work with Feshbach.
You also have a paper with —
And this is, oh yes, this is the most remarkable phenomena that you'd be interested in. If you have a plate so large in transverse dimensions that the supports are a long ways away and if you press against the plate the velocity of the wall is proportional to the pressure to your force, and it will stay that way until response from the boundary comes back, and recognizing that enables one improve upon what Feshbach and I did. So whereas this dashed curved is the formula that Raman developed this data continues here. When you do it properly this curve becomes this curve and goes through all the points. So to some extent this is an amplification of the work that Feshbach and I did. And as a consequence of this is why I went where I did during the war. They thought it would have something to do with impact of projectiles on plates.
Let's see. Is there anything important before we go to the war to say, there's a whole series of papers now that you did in consequence of the internal friction work, one on thermal currents, intercrystalline thermal currents with Randall and …
With the specimens that Cyril Smith was responsible for. I don't know if are you aware of what he had to do? I mean of what Cyril's job was.
No. I haven't spoken to him about that.
You see, the peak in these curves occurs in the middle of the isothermal and the adiabatic region. So the peak occurs where the time for diffusion which is the grain boundary area over diffusivity, this gives you the time of relaxation, for that time the frequency is one, is where the peak occurs. So in the experiments, we varied f and Cyril gave a specimen for which he varied the grain size, so by combining this number all the points no matter what the frequency of the grain size should like above one curve. And that's what would happen and that's what did happen.
Some of the other people who are around when you were doing this work at CCNY besides Rose and Randall. Were there others who you worked with?
They were the main people. And were they in the department?
Others, yes. Most, let me, I will always have a soft heart for City College, City College of the College of New York. Almost all the faculty had been graduate students at Columbia, so they went to Columbia for their research work. City College was a full-time teaching schedule, nevertheless most of them did carry on some work. And I have an interesting story to tell. When I went there, I had come from Washington State, where I did my experiments on reeds, braids? And of course they had equipment there. So I asked the head of the department if I could have a laboratory and he asked if I could get funds to get the equipment. Well, in those days, $500 goes a long way. So I got a $1000 grant from the … foundation. After I got the grant, the head of the department —
In these papers done at CCNY, you often acknowledge the Penrose Fund of the American Philosophical Society and also the Rumford Fund of the American Academy of Arts and Sciences.
Oh, I'm sorry. I've forgotten about that. I don't speak of the Engineering Foundation?
I don't know. Maybe in some of the papers, this one for example here. Anyway, you got the money.
Yes, so the head of the department and I walked around to find a place.
Who was it?
I was trying to think. I thought he was a very good head. He wasn't liked by my colleagues, but I thought he was terrific. I don't think he had a Ph.D. but still he made a good head of the department. Well he took me around and stopped at a room, well we're no longer co-educational, this had women marked on the door, and he said you can have it. He refurbished it. It was the only laboratory in the college. Well, why I have such a fond soft heart for City College the teaching was at least in physics was very good. They had a crew from Columbia that were dedicated to teaching. Most of universities at lunch when the faculty it's not considered proper to really speak about pedagogical problems but they did there. This was of major concern. The classes were restricted to 20 per class and …
Could we stop for one second? I think this is giving us problems here this I don't like what I hear in this machine. This is why one uses two. You can continue now. I'm sorry.
The students were selected by grades. They were start from the top of the applicants from the high schools and work down until enrollment was filled. And as it turned out, 95% were Jewish. But those boys knew they had to strike against them, and I have never seen students work as hard as they did. We didn't have to spend any effort in interesting them, they were interested from the word "go". So from that standpoint it was a pleasure to teach because of the students.
Were there any who you remember who subsequently became known in physics?
Yes. The most outstanding one is Nuremberg and Scripps. He was there. You've asked me a tough question, because I know of Nuremberg because he came to see me, and wanted to work in my laboratory but this was just before I was leaving to go to Washington so I couldn't have him that's how I know he was there. There may be others but I just wouldn't know their names.
But anyway they made a big impression on you.
And the contrast between City College and Washington State where I went to was just tremendous. In Washington State I would come into the deans and we weren't very hard we weren't very strict and he said all of our graduates have no problems getting jobs. The contrast between that spirit of them being happy because they got jobs.
Did you go over to Columbia to work as well or did you … the city in your new laboratory?
I went there a lot to the library. They did have a very good library. As a matter of fact, I was there so much that the librarian didn't feel like she should welcome in … so much so I went to see … who was the head. He cleared it with the librarian. So I used their library.
And the main work in this period was the internal friction of various which was very well confirmed. And then you go to Washington State University in Tacoma, Washington as an Associate Professor this was 1940-42. What is the story behind this transition?
Oh, yes, that's interesting. The head of the department there I can't think of first name, Paul, on the trip east stopped at Harvard to see Bridgeman, he had worked with Bridgeman said he would like to have someone new to expand the department. On Bridgeman's advice, Bridgeman suggested me, at City College we got along fine so I joined him there.
Did you do some teaching there too?
Oh yes, yes. But not the l6 hours a week.
It was more attractive in the fact that you had more time for your research.
Oh yes, sure. And also a terrific place to live. I would always recommend it.
Opportunity for camping.
How about the rest of the department. Were they interested in physics?
Again, it was rather like Washington State in that I was relied upon to supply theoretical stimulus.
Here you wrote this paper on the interelasticity of long plates that we mentioned earlier which you went back to the Raman work on hard spheres and you also continued work on the theory of internal friction introduced by … this time.
I would like to speak of an experience which I'll never forget. You're aware of course that as you raise the temperature you expect things to become softer and more plastic so you expect the damping to go up as you on general principles to go up as you raise the temperature. I'll never forget the night when I found that we went still higher, it came down. I didn't understand it at the time. It took several years to understand what was going on. Again I think this was a specimen that oh yes Cyril I had been in correspondence with Cyril Smith for a long and I told him I wanted to have specimen where the thermoelasticity friction was as low as we could obtain it. We had to avoid the internal friction due to intercrystalline thermal currents that meant small grain size and low frequencies, and low frequencies meant transverse vibrations but then the specimen had to be so thick that it was essentially isothermal with respect to the transverse vibrations. So it was designed to be right between these two peaks. It was really spooky. You would set that vibrating, it would go for half an hour and you couldn't see any appreciable decrease and this is then what we used to study and it was this specimen that I took up in temperature and found once it reached around 300 C and even higher, it came down again.
You're referring to this note here, this letter in the (???).
Well let's see where I don't think it was until after the war that I understood what was the experimental results you're referring to.
It's in a letter to Arthur Barnes.
Oh, no this would have been. and Cyril Stanley Smith, that's '42, (???). Well, Cyril Smith was. You'd better turn that off.
We're resuming after a very nice lunch. Before we go to Watertown Arsenal, I had one more question about internal friction. On your paper on the theory of internal friction introduced by cold working, you suggested that due to the inability of certain areas on slip planes to maintain shearing stresses. This is a completely different point of view from that of Seitz and Reed which —
Is it really different?
No, maybe it's not.
You see when I speak of not being able to withstand shearing stress, there are dislocations which move in response to friction so that stress is less than it would have been because the motion of the dislocations. So it's a difference between the macroscopic and microscopic interpretation. This is most marked you see when one in one of these paper I calculated the difference of the elastic myulae of different crystalline materials if the grain boundaries could not withstand the shearing stress and got a different modulus depending on whether it couldn't or could. And then we did experiments which. Now you see Seitz and Reed would probably say the grain boundaries are simply a lot of dislocations. Well, okay, perhaps they are, but I'm saying it doesn't add to the interpretation I'm telling them or this is the way I would tell them in the past I would challenge you to make a prediction based on the dislocations that I have made based on the concept of viscous behavior. So I would say that it's a difference in viewpoint. It's not appropriate to say one is correct and the other is not correct. But it would be pertinent to say which is more productive which leads you to the most fertile experiments. I have always or usually am concerned with only doing theoretical work that could lead either to interpretations of past experiments or prediction of new, not calculations not just for the hell of it. So that's why difference that you have observed in language.
And this as a matter of fact is characteristically the difference between Seitz and myself. In a lot of our work in this period, he concentrated —
Okay, you were commenting on the difference between Seitz and yourself in this period.
Fred is a person who concentrates on single crystals with the hope I felt that once he understood everything about a single crystals then he would understand the aggregate. I did not share that opinion that an understanding of single crystals were as desirable, that it should necessarily precede work on polycrystalline materials. It reminds me very much of the difference in biologists in the micromolecular biologists and the physiologists, whereas it's desirable to understand as much as you can about what's going on on the microbiological scale, there is also fruitful work to be obtained on the larger, macroscale of how the organs function. So work can precede at different levels, one might say of sophistication and you don't want to wait until what you might call the most basic problems are understood before you start thinking on the larger scale where you are not as concerned with the individual molecules. So that's part of the difference.
Let's see, in '42, you moved over to Watertown Arsenal, in Watertown Massachusetts. You stayed there for about three years.
Until the end of the war. It seemed like more than three years (laughter).
How did you get there?
How did we get there? Oh, we drove. No, I mean by train.
No, I mean —
This is interesting though. This was in the middle of the winter and I was in Washington State after Pearl Harbor and in the West they just didn't know what to expect from the Japanese so they had no weather predictions by radio except travelers coming through spoke of a terrific amount of snow and we just had had a baby so we sold our car and went by train. So that's how we went.
How come you chose, or did they choose you why Watertown?
They told me they chose me because of the impact of that I did of objects striking plates.
I see. And who told them about this work?
Oh, I don't know except there was a physicist there by the name of Lester, Horace Lester, you wouldn't have heard of, he was a radiologist, he was the principal physicist there. It was because of him.
Somehow he had heard of your work.
That it was related to their mission.
Now it seemed to me irrelevant. Some other place wanted me to come because of my internal friction work.
Which place was that?
Bartot. I couldn't see the relevance. But I did see the relevance of the original work, whereas that particular work was irrelevant the kind of thinking was relevant, and I think we did a lot of work.
But tell me about the place about what they were trying to do and about the environment there.
Yes, that's very pertinent. Fortunately, they had a terrific guy in charge of the Arsenal, or in charge of the Laboratory, Colonel Zornig.
Have you run across?
Z-O-R-N-I-G. And he was quite a maverick in the army. He had been the military attach; to Germany during the declaration of war against France and had previously he had been the military attach; for several years prior to that, and he felt the best way to learn about the Germans to be a spy was to enroll in their military college, so he was friends of all the high generals, and rode in their staff car into Paris and then in a staff car to observe their bombardment of Dunkirk. So and he had previously been director of the laboratory at Aberdeen in design of bombs, the projectile. To understand how they —
Was that some place in Maryland?
Yes. And he would get a plane someone else and he would take the camera with instructions to follow the projectile down and he would photograph how it flutters and yawed and so forth. I'm saying this to let you know what a terrific guy he was. Now, when it came to whether we should publish our papers or not, he insisted that they be published contrary to what his immediate bosses thought, because, he said, if you don't they certainly will remain secret from the Germans but will also be a secret from the U.S. people who ought to know. So when you asked about the environment it just was an ideal environment.
That was very unusual.
Yes, and he was such a maverick that he never got a promotion beyond his colonelship during the whole of the war.
So all the papers were published?
We had reports, internal reports, and then we would publish —
In the regular journal.
That was most remarkable.
That's amazing. One of our biggest problems in this particular project is the work done during the war, which is hard to find even if it's not classified, because it was never copied in large quantities, and they're going out of existence, so one can't find them. So this is an exception.
And he encouraged our work trying to find out what was going on, both to the plates the projectiles and to the bullet, and so you see they
Was that the main problem that was being studied at the arsenal or were there many of that sort?
That was the main problem they were concerned with armor and also the making of cannon, there was the laboratory was the production was with large casting of cannon. The work that we were but there was nothing apart that you can see. We did have a paper on quenching of cannon, not a cannon but tubes. But that was published.
Was there a large group or a small group. I mean did you work together? How was that? Tell me something about the schedule.
Okay. It was built up very rapidly. And I was the only physicist there, brought a graduate student, Van Winkle who had been at Washington State. Most were metallurgists, there was one metallurgist in particular whom I liked talking with Herb Hallamin.
Now there's a J. Hallamin.
J. H. Now it's interesting he was they made me head of the metallurgical physics and made him the head of physical metallurgy, so we had a lot in common (laughter). So we sort of made a pact between us that he would teach me metallurgy, and I would teach him physics. So that's where I really started becoming a metallurgist, and it came about in the following way. The primary problem in armor and projectiles is to make them hard and ductile that is and in general it reminds me very much of in economics, there's a curve the lines curve in economics on one axis you have inflation on the axis you have unemployment. And economists there's always a trade-off between one and the other if you're willing to reduce you can always reduce unemployment by pumping enough money in and bringing about inflation. You have exactly the same kind of trade-off with hardness and ductility. If you're stupid and just raise the hardness in the standard way, it becomes brittle. You lose ductility. And you can't have just things crack one doesn't want that. So the problem we had with how to you not only alloy but once it's alloyed how to you heat treat the material? To increase the hardness without sacrificing ductility. And that turns out of course that's the in armor plate and projectiles is primarily steel so that's and again I want to show you something else in connection to in '48, French people can only read French.
What it turns out to be is this large summary of our work at the arsenal.
I see. How did they happen to write a little monograph.
It wasn't secret. It was published, and they take our journals, and as he says in the introduction, a lot of French don't read English, so they felt they ought to
Write it up in French.
So they took most of our papers and so I really felt that this is quite a tribute.
This book is called (???) and it's by Yves Dardel and it's published by the Centre de Documentation fiderugeek Paris 1948. Maybe before I leave I would like just a xerox of the title page and put that in the file. Well actually it would be nice to have the introduction. And the first pages as well, the table of contents and the first few pages as well. Well, it doesn't have to be done. (pause in tape)
This is to me a terrific example of the stimulus of basic research trying to work on an applied problem because there are people here now purely in (someone enters room) oh, hi. … I'd like to you meet Mrs. —
Hoddeson, right? Oh, we've chatted.
On the phone.
How do you do?
Could you please, what you call —
This letter in the front.
Okay. Copy the letter. Sure.
From the title page to the introduction just up to —
Sure, be glad to. (leaves the office)
Oh, there are people in the physics and metallurgy department continuing basic work based on one of the papers we turned out, namely, when you heat treat the you start with the iron with a carbon in solid solution then you lower it to a certain temperature and the carbon comes out in parallel plates. There are two ways that it can come out, and one way is in parallel plates, of sementite and …? And this advances by diffusion of carbon to the ongoing … The problem arose how fast does this move? How is that affected by the temperature. And one of the papers here discusses this problem and shows that the standard theory is incorrect. The theory was developed by one of the people here. And predicts how it should depend on the various parameters which have been found to be correct and improved upon by people not working on that subject. In other these plate structures occur not only in iron steel but in a wide variety of metallurgical substances.
So now there's a paper on internal friction of an a-brass crystal that you wrote in connection with your work at the arsenal the issue is whether the internal friction of single crystals is attributable to inhomogeneous.
Oh, that's right. I was searching around for an interpretation of the work which we had performed in Washington State and it turns out I did not have the right interpretation at this time I thought I did. But I did not.
The paper you wrote with Hallaman on the conditions of fractured steel shows that in it you find that the deformation has a negligible effect on the fracture of steel and this is a paper in the Transactions of the American Institute of Mining and Metallurgical Engineers. Apparently this led to a whole series of papers on the strength of steel.
Yes, let me again at this time a lot of laboratories were working on how the strength of steel how the stress necessary to produce … depended on rate of deformation … we recognized that you can eliminate most of this work by varying at the same time that you vary speed you vary temperature since every physicist knows that things speed up as you raise the temperature and by a very simple law you only don't know the heat of activation of what's going on. So this paper and some of these other papers were related to demonstrating how you can obtain much more for a given amount of work if you work at different temperatures. Now this work in the journal of applied physics in '44
On the effective strength rate upon plastic flow of steel.
This I wished to emphasize particularly since something very important in general came out of this. As I said, a lot of work was being done on the effect of strain rate. And this work that was being done missed the main point the effect of strain rate does in fact influence the stress level perhaps 10, 20% but even more importantly the difference in going from low speed isothermal to adiabatic deformation can make a tremendous qualitative difference in behavior and that's what this is about. You probably missed these papers are so long I don't know how we wrote so much. I mean, we weren't being paid by the word. As you keep on straining the mixture at a given strain rate, the stress required to produce further strain goes up so to speak … hardens. This is what happens if you put … under isothermal conditions but again all through my life I have been been working with adiabatic and isothermal and the differences between the two. Now with adiabatic deformation you are having the strain hardening, true, but you're also just temperature per se weakens the material so you're having this weakening effect of temperature induced by deformation so if you plot a stress strain curve stress strain isothermal it keeps on going up.
But adiabatically you plot it, it would be the same at first but the deviation will get larger and larger and you'll rich a maximum. Now if you are not straining this at a constant rate but you apply a load, so you have control of the load but not your strain, once you reach this maximum then this goes up suddenly and if it's sheared you will shear it off just along one plane or as Seitz and Bardeen would say your dislocations are involved along one plane. And then we did experiments to demonstrate that and this … experiments I am very proud of. This experiments in a dye if you have a plate supported by a dye and then you … you just push slowly it forms it deforms and then tears, if you drop it, if you drop a weight on it, not so it goes through, but so it goes and then you take a section. This white means that it has become so hot you see it's past this point. All further deformation is concentrated. It melts but it's quenched by the surroundings, and when you quench steel it turns to marzite, which when you etch it, it's very hard, and when you etch it it shows up as white. So but the essential thing is in going to higher speeds but once you once the speed is high enough so it is adiabatic deformation that's the major effect because then it changes the whole pattern of deformation. You create these ranges for … it concentrated. So and then we show that rather than having a dye if you simply have a plate and fire a projectile that's … the same thing happens. And that is not in this paper, this was in a later paper.
I think it's this next one here. Plastic flow and ruptured … Is it this one? Could it be this one?
No, this was a —
Let me change tapes.
When the war ended and I went to Chicago.
You wrote up some of this work.
You're right. And carefully. And this is a picture of but here's the set up. Punch slowly, it just cracks.
This is the paper on micromechanism of fracture.
I'm telling the recorder.
If you apply a tension a lateral tension, the planes of maximum shear stress are not vertical but … and that demonstrates oh I'm sorry when you have a compressive stress and this shows what happens when you have a projectile with a blunt nose. Ah! When you have a tensile stress, it comes in this way. In … to obtain a barrel shape one would bend the stress bend the plate so it's compressive at one side and … the other. And reducing it under a tension would curl it up so we could predict what kind of punches one would get by the stress system that it is subjected to at the time so we could make the predictions at a facility for going on and firing these projectiles. So it was a lot of fun. This work I'm very proud of, because the concepts are simple, but it never been plotted before.
In many of these papers you refer to the work of Grifith, done in the 20s. In France, and the work on fractures, especially. Is this work I should be going back and studying as a basis for the —
Let me say Grifith's,
The only other name that comes up is Ludwig.
Ludwig was more the stress system one should yield. There's a question as to what the stress what is the stress system that causes plastic flow? And Ludwig's name is associated with that.
And Grifith's with the sensitivity of fracture to microcracks and everyone that works on fracture now refers to Grifith's work.
Was it well known at that time?
I presume so. During that period I had a library of a lot of standard metallurgical books, so whatever you don't have to ask me where I got these ideas, I just devoured the literature.
Right. Bridgeman's name also comes up.
Yes, that's right, because his see he did a lot of work using his high-pressure techniques on everything that could be measured and the effect of high pressure in suppressing fracture no one else had the facility that he did in the interests so he did his own work and he worked with us at the time. Not with us.
But you were in communication.
I was telling you but stopped about the collaboration between Herb Hollaman and yourself.
Yes, tell me more about this. This also connects with the comments you made during lunch about. I asked you when did the metallurgists start talking to each other and you said that Cyril Smith was —
One of the first I knew of to my knowledge. Now after the war, Herb Holloman went to GE, head of the metallurgy department. After the war, after several years thereafter, I went to Westinghouse, my first duty was the head of the metallurgy section getting it started. I was in competition there with Bert Holloman. Then for a while he went to the Bureau of Standards. And then as president of the University of Oklahoma, I wound up as Dean of Science just south of Oklahoma at Texas. So we have followed very parallel paths since then.
This paper on an elasticity of metals goes back to very early history.
That was a review. There's nothing.
You have, the elastic aftereffects in iron wires from 20 to 550 C.
I would I have spoken to you at length on thermoelastic damping. There's another kind of damping which appeared first in iron … the Dutch physicist —
No, this was Snoek.
Snoek, that's right. S-N-O-E-K.
Snoek first demonstrated this. And you're aware of what's going on in this effect?
Not really, no. You'd better explain it to me.
The interstitial positions in body-centered cubic materials do not have to … tetragonal symmetry. Depending upon which position they're in since they have tetragonal symmetry. There are three types of position, tetragonal, those interstitial positions whose tetragonal active points along the … axis and under ordinary conditions those stresses they have randomly filled but if you extend but if you have a tensile stress along the x-axis you have a preferential occupation of the x-tetragonal compositions under the compression there's a preferential depletion. So if the period of oscillations is comparable to the time of relaxation you get a damping so if you vary the internal friction as a function of frequency you get a peak and this is called the Snoek peak. And he utilized that particularly in Chicago as a basic tool for investigating the metallurgy of steel. Should we go into this now?
Sure, why not. Let's go on to that. Then … fill in some of the background to the University of Chicago as well. Let's continue on this.
I said that we get a peak at that temperature where the frequency of vibrations is equal or where the period of oscillations is equal to the time of relaxation or to the jumping time from one position to another. Well, by varying the temperature and getting the peak at a different frequency we can measure the effect of temperature on jumping rate. The jumping rate, of course, is related in a very simple way to the diffusion coefficient. So in that way we measure the diffusion coefficient of carbon in iron. And by combining a measurement made at very high frequency with measurement not of internal friction but of relaxation phenomena … where you are measuring the same physical phenomena we get the internal friction over we get the diffusivity coefficient over a factor of something like 106 cycles higher than I have seen any physical property measured. Now the other characteristic of the peak is its height, and the height of the peak is proportional to the amount of carbon in the lattice, specifically to the amount of carbon that's in solution. So we have a method of measuring the amount in solution or the solubility of carbon in iron and how it depends on the temperature at which you make it. Now, the ordinary diagrams of solid … in iron show that at some 200 C the solubility remains constant. But these were obtained by making macropictures and finding that they don't see any more precipitation but this is a very crude way and we had quite a discussion with the standard metallurgist who wouldn't have at first believed that the solubility tended to drop as the temperature dropped. So we had these two basic bits of information that we could obtain that hadn't previously been obtained namely the diffusion coefficient of carbon
… something I thought of for later.
And the solubility and the amount of solution. Using those two, we could get at the question of how rapidly does a precipitate particle grow, it's coming out as a spherical particle; how rapidly does it grow? And that is obtained by finding how rapidly does the carbon go from solution onto a precipitate? So this was a question that the metallurgists hadn't had a handle on before, and carbon's not the only solid that behaves this way. All the interstitial alloys of iron behave in the same way, nitrogen, and oxygen, and iron's not the only metal that has these tetragonal structures, all body-centered cubic have tetragonal symmetry in their interstitial positions. So this opened up a new area of investigation for us, chromium, molybdenum, there are a group of six body-centered cubic metals … so this is an area that sort of an offshoot of what we've been talking about.
And it grew out of the war work? So it was continued at the Institute for the Study of Metals.
Yes, but mostly elsewhere. I don't like to continue too long. A lot was continued by the authors of the book that I showed you. He was the main he worked at Chicago for a while and then went to Columbia.
I see. So tell me about the, you got to Chicago in 1945. Was this just at the time that the Institute for the Study of Metals was organized?
Yes. As a matter of fact, I was there before Cyril Smith.
So if you could tell me a little bit about that history, I have not yet spoken with Cyril Smith about these subjects. I don't have any —
Of course, I only came in when Cyril Smith when he had been invited to head up an institute and I get confused about when the war had been but certainly once Japan capitulated it was obvious to us all that the end was coming soon, so most of those people in war work were really anxious to get away, and it's interesting, my speaking about that reminds me of a visit from some general the next year. He wanted to know why people wished to leave, to get out of the army. And I one of the reasons simply you can't fire people.
There was a lot of dead weight.
My son who was a general consul for ETA found the same thing. It's almost impossible in the government. I think that Carter has changed the rules so it can be done.
Tell me more about the Institute for the Study of Metals. Whose concept was that, do you know?
No, and that you will have to get from Cyril. Let me say as I heard it second or third hand, Hutchins, who was reportedly antagonistic to science originally was converted by the work that the Manhattan project did which started at Chicago. He thought it would be a lost opportunity just to let these people dissipate, so through conversations with other people he got the concept of … institutes of which there was the chemical institute which I think folded up, and the nuclear institute, so there were three that started and two survived.
I see. And what kind of group was it? Was it composed of metallurgists mainly? Was it a mixture?
I would say a mixture of metallurgists, chemists, and physicists.
Were they selected by Cyril?
Yes, exclusively. I mean he had to give the OK.
Was there something special and unique about this and environment in comparison to other places you worked at universities or perhaps it was more like another laboratory?
Oh, no, not at all. It was, no, it combined let's say, the people that were joined the Institute were given the opportunity of also having a joint appointment and I chose to be joint with the physics department so I also taught the physics courses and there was not a metallurgy department but the chemists on the whole to teach in the chemistry department. Now this was not for extra pay, but that's the only way of getting association with the students, the best way.
At that time, I gather Chicago was the number one university for physics. Or is that overemphasizing its importance?
No, that's right. Wenzel was there, Teller was there.
I'm not sure that's right, but I got that impression.
I think it was.
I don't know how long it stayed number one.
Maybe two or three years.
But certainly right after the war. And I also gather that there were certainly by '49 when Seitz moved to Illinois that there were fairly close relationships between your work up there and Seitz and workers down at Illinois.
Were there visits? Or was it mainly letters and phone calls, and things like that?
I think mostly visits. But not periodic. I would say …
What about the relationships to Argonne or other labs where solid state …
Let me say, you see Fermi was in the Institute for the Nuclear Institute and he and his people of course had a lot of interactions with the Argonne people I personally did not have I was about the only member who hadn't been on the Manhattan project. So I didn't have those ties. So I can just say I don't know what ties Cyril had.
There was important work that was started at the University of Chicago during the war on Radiation Damage under Wigner. I was wondering if that continued at the Institute for the Study of Metals.
It was picked up at other universities. Such as … Okay, well, there's an awful lot of work that you did at the University of Chicago. I don't know whether it's worth going through all of it. We've talked about some of it. A little paper on the defense of the Cauchy …
Oh, forget that. You can't —
You can't do it all.
One usually writes when you see a solution, you write it up. But it's rare that, oh, when
There's an interesting paper on the contributions to the theory of b-phase alloys. I don't know whether you consider that important.
Well, only in the following. Terry Jones had written a paper which I disagreed with. So I wrote what I felt was the correct interpretation. But I felt that this was no influence. In this group though there is one concept which I recognized and then applied in quite a few places. Namely, the following: if you introduce residual stresses in the lattice, by any mechanism, by putting in a larger solid and say introducing a dislocation but anyway that you distort the lattice, it's going to reduce the elastic constant in the immediate vicinity of the distortion which will be reflected in two ways. It will be reflected in the reduction of the macroscopic shear modulus. Secondly, it will have you have a distortion when you have, when an atom is diffused, it has to go through a potential barrier, when it's sitting on top of that potential barrier, it's distorting the lattice, it's pushing the … aside. So the elastic constant of the surrounding material the … constants are less. The lower the shear constants, the larger the amplitude of the vibration of the atom, so the lower the entropy. So (tape ends)
— over rT, …
Now this —
— term, there may be a constant term, but it's essentially a2/t, where a is the jumping distance, t is the mean time the atom has to wait until it adjusts. Both of these one can, well, a you calculate from the geometry, t you calculate from the … I'm sorry, a2 times the frequency of vibration then this is the chance of jumping during each vibration. But the point is this you know you know from the elastic constants, so this you can —
a2 and z you know, right, from the elastic constants, and so you get do —
You get do except ... I have one more term which is Ws/k where Ws is the increase in the entropy of the lattice when your diffusing atoms. (Woman enters). Ah, thank you.
Maybe. Nothing right now.
Thank you very much.
Let me consider a model. These are two positions … if I like to think of them, you have the atoms confined to a plane perpendicular to the … and you're asking what is the work which we would have to do to move this slowly from this position to this position and then the calculations will show that d is equal to this this a2n times e-Wg, the work which is due. And Wg one can then write as h - Ws. And this is where then this Ws comes out and then the + sign. And this is then so our Wg is dependent on temperature. When you pick the temperature effect power by writing it in this form. Now this involves a lot of arguments with the editor of the (???)
They wanted the T there.
But it the temperature is that if you make a plot of Wg = 1/ …, and in general it's not one has a line not horizontal. And the slope of this line is Ws, and just a moment, no, I'm sorry, the slope of this line is just Wg, the slope of the line against 1/T is your h, and this 0 means infinite temperature, so this is our this part yes this is the work part would be if you gave it an infinite temperature. This has been a lot of work has been done, oh there was a lot of argument as to whether this extra term was + or -, this work conclusively showed that it let me that it's positive, because we are decreasing the elastic modulus, so heat flows in to keep the temperature from if you decrease the elastic modulus isothermal heat flows incidentally this shows the relation to thermodynamics and I'm quite horrified to find that very few physicists are even aware of how to use the first law. If you want to have a trick question you can ask the following question of your colleagues. You have a water and you place a copper rod in it, and then you compress the copper rod by putting a weight upon it and you ask is the energy content of the copper rod increased or decreased?
I would think it would increase, but I suspect it probably decreases from the way you're setting up the problem.
You would suspect it would increase in if this is the amount that it is compressed in the quadratic way, but if you look at the heat, you'll find that is linear and a linear law always wins out if your at low enough stresses, so the heat which flows out is more than the work which you put in.
But it is very surprising how in college today one is not taught the elementary principles. I'd like to pose a question of the same type which I would think you'd be interested in in which you know your first impulse is to give the wrong answer. If you have a bomb, a chemical pressure bomb, and you have a gas inside the pressure bomb, then you take a blowtorch and let the system to go equilibrium. Is the average kinetic energy of all the particles in the system, (???) the particles, electrons, protons, not inside the nucleus that's unchanged, is the average kinetic energy decreased or increased?
Again, you'd think it would increase.
And I feel very bad about the German physicists, …,
The one of the second law?
Yes, because he developed a theorem which if physicists knew as much about matter then as they do now, he could have really gone to town. You know what's called the virial theorem. I'll just repeat it. If all forces are central forces, attractive or repulsive, like Coulomb's law, then the average of the potential energy is the negative of twice the average of the kinetic energy of all the particles. Now if you neglect relativistic effects, and magnetic effects, and consider only the electrostatic interactions between electrons and protons, all these are the principle forces they satisfy the requirements, the Gidel law still holds. So the energy of the system if this is zero, is composed of potential plus kinetic and the potential … and then I come up to get the total. But the total is always half of my potential. When I add energy to the system this line comes up, so my potential comes up part way and my potential is … and so my kinetic energy is reduced to. So in spite of the fact that the gases are moving faster and that the atoms in the wall in the steel wall are moving faster, the electrons in the atoms are more than making up. Now in the very simple example for instance you take H2O molecules. And then you pull it apart so it's now rather than a stationary molecule, you have two stationary atoms, the virial theorem says if you put energy into the system so you put energy in so this is not as far down as this … and half of that is kinetic and that's less than before. So the atoms, the electrons in going around their isolated patterns are going more slowly than they were when they were hence of course it's obvious that they aren't, but this is a general principle which Clausius would have recognized was true, if he had known about atomic structure. But this is an example of the lack of appreciation of some of these very general thermodynamic principles. I think it's a pity it isn't recognized because I enjoyed life more recognizing what's going on out there.
Tell me what about this paper on relaxation phenomena in metals? Do you consider that major?
No, that's a review.
Then we come to the work of Charlie Weart on interstitial atomic diffusion.
That's what was I was talking about.
Earlier, right. Well, there's a series in this. Growth of … elasticity.
Here I want to someplace oh there was a German paper.
Oh yes the German paper is, I have it somewhere. That's a little bit later. Here it is, it's l953, thermal damping.
Let me see that because that is not the …
Oh, there a few that I couldn't find. It may be that they weren't at the University of Illinois. There were a few in that category, so maybe you're referring to one of them.
I would like to have you got the impact of
Yes, I have that one.
I was looking for a paper that quoted Kester's work on elastic constants, showing that Kester showed that if you take … and plotted the shear modulus against the concentration of solids that you would get usually it would always go down and this paper pointed out what was happening was you were introducing local stresses and I obtained again this is a thermodynamic relation equating the change in modulus with temperature with a change of modulus with … and showed that indeed these slopes were determined by the temperature dependence of the elastic modulus so this is one more example of this relationship. That was what I found frankly fascinating in this work was once you got onto general principles.
You could apply it many, many, many different places. Right. Let's see. What about the work on ring diffusion in metals?
Yes, this was a one-shot thing.
Well, then you do an awful lot of work on the diffusion which we've already talked about and then about 1950 you started working on ferromagnetism.
That had a central theme too. The central theme, I can't say it's 100% correct, but I think you'll still find differences of opinion today on people who have studied this more. Heisenberg had a great effect when he worked in ferromagnetism showing that ferromagnetism is a change of the sign of the interaction between co-shells. Are you familiar with this?
Yes. This is his classic paper on ferromagnetism in 1928.
When I was at Chicago, I got another idea which involved it doesn't really change the sign. But something else is taking place which is always taking place and then what else is taking place is that closed shells always repelled one another but that the spectroscopic data shows that if you take an electron outside your closed shell let's say you have a half-filled shell you take an electron outside like … the lower energy is always such that the spin of your other electrons in parallel in the inner shell. So let us consider a conduction band where you have half-filled thin shells, whereas these shells all by themselves would like to point in an antiparallel way you have an effect which tends to make them parallel because if all if you had a predominance of electrons all pointing up then and they are traveling not all through so aren't limited to one atom, the inner cores would want to point parallel to the direction that most of the electrons are pointing. In particular if the shells are so far apart that they are not interacting, then you are going to have then you will get this spilling of one conduction band with respect a raising of one conduction band with respect to the other if the spins are all pointing the same way. Did you read that paper my first paper on ferromagnetism.
Well, this first one is the one on just interaction between d shells in a transition. There's another one on ferromagnetic compounds.
I think it was
There's one called the intrinsic and antiferromagnetic … that's the fourth in a series and —
I think it was, this can be neglected. Oh yes, this one the one the first one.
Interaction between the d shells of transition metals. (???)/4, p. 440.
Oh, yes, yes, in the abstracts it is demonstrated that the spin coupling between incomplete d shells and the conduction electrons leads for a tendency for ferromagnetism among the d shells. This was seemed to me to be a simpler interpretation of ferromagnetism than the interpretation that Heisenberg gave and then
I gather Slater at first didn't respond well but then adopted it.
I don't know. But the really interesting from your standpoint was after writing this, I then really searched literature hard to see if any other phenomena could be interpreted and was delighted to find out about this work in the 1950 oh well that had just come out
Let me just change tapes.
These guys had published during this year.
Yonker and van Senden. Had published just at that time.
That's right, they did the experiments which you —
They found that electric conductivity was associated with the presence of ferromagnetism. In their case, the d shells are way apart so the only ferromagnetic interaction they can have is the jumping of the other electrons which are more loosely bound and these electrons can only move by exchange I call a double exchange their motion is associated at the same time that they couple adjoining these structures are … structures only have this property if they have mixed bands, are you familiar with this?
So you have a jumping from a double plus to a triple plus. That jumping can only occur between those ions whose spins are pointing the same way. So conduction and lining up of spins are coupled together so that is and one could establish quantitative relationships so that worked out very well then it's also worked out in the second row of transition … where the d shells are not coupled to one another. But this you were asking how one got ideas. I was looking for the idea.
Sometime during this work you switched to work at Westinghouse. How, or why did you switch and —
Well, that's a you know there are usually one than factor involved. And there are two factors firstly the financial factor secondly I was getting rather tired of being a professor. True, I was always working on something new but it was a repetition. And so I there was the financial factor and there was I had never stayed as long at any place as I had at Chicago. And —
You felt like moving on. Okay. The environment must have been very different, because Westinghouse was an industrial lab.
Yes, it was different.
How much basic
I was certainly not as productive there but that wasn't my job. On the other hand (break in tape)
Excuse me, you couldn't have.
I couldn't have been doing the work I now am doing if I hadn't that background. So I'm glad I changed apart from the financial aspect. Because you see a lot of people feel like I feel that we should develop other methods of obtaining power or energy than mining our resources. And that process is going to win out which has the lowest capital cost and to recognize what goes on into the final capital cost and how to handle the optimization is crucial so I feel I would certainly not have tackled what I'm tackling now if I didn't have that industrial experience.
Could you tell me I haven't interviewed anybody from Westinghouse up until now. And I was just curious about the level of basic research that was going on there at that period. As compared perhaps to Bell Labs, places like that.
I think that I should give you a lecture here.
Because I was not I did not like the talk that was going on at that time in a lot of industrial laboratories in hiring people you can do whatever you want to do here. Because with my experience in the war, I had felt that practical problems can contribute can help … just about the time I went to Westinghouse or somewhat before the U.S. Steel set up their new laboratories out at Monroeville and they did what I thought was a terrible thing. They separated their applied from their basic research. They had separate buildings separate directors who reported to separate vice-presidents. Now they no longer have a basic research laboratory. There's one guy out there whom you might want to talk to … I can't recall his name. Well, it's a terrible thing because to separate the two. I felt it was terrible at the time, and all talk at Westinghouse in trying to separate the two I would oppose just because I felt they each helped one another. There was big talk that well in case of emergency the company might stop the basic research. Well, it turned out at the U.S. Steel they eventually did stop them all. And I think they felt that because the problems which they worked upon weren't of interest to basic scientists but not to the conduction people. Now here in our metallurgy department we have quite a few. Kun Lee is one who consults a lot on the processes involved in making steel. Now most of the solid state work you find in metallurgy are on the physical metallurgy side, the properties of the … and practically none on how do you produce the materials? There is some work on the zone refining that solid state physicists get into. But the big problems in the steel industry the big problems are involved in the foundry, and this involves what goes on when you solidify the materials when you quench and so on, so all these this type of problem was sort of debarred or automatically ruled out for the basic research laboratories because it would have been called too applied. But that's the only way the young guys interested in what's going on is to get them involved. And that's why I feel the National Science Foundation has done a disservice to science by defining basic research and applied research and depending on what went on. Now they did that, in their defense, in response to Congress, I think Congress asked them to, but they should have tried to influence Congress so they wouldn't have asked such questions.
But to back to Westinghouse in that period. I gather they were making the distinction.
Let me say a small group in the physics were making that decision and they were the most unhappy group of people. I mean they essentially avoided problems which would have been practical and I didn't feel that was very healthy.
Was there much interchange?
I would like to ask you spoke about the Bell Labs. I when you had an opportunity with the Bell Labs people I would like you to discuss this question with them. But my belief is that they have the right attitude, namely that all their people work on problems that the management sees that if they succeed they will open up new products and I'm quite I mean my impression is again I would like to know firsthand that everyone has someone leaning over their shoulder to see what can come out.
I don't think that's true. I think that there are people at Bell who are simply hired to work on pure problems, pure research problems, although the management does choose to hire people whose pure research is likely to lead to application relative to communications. However once they're hired, I don't think there is anybody standing over them. I think it's only in the hiring process.
Well by standing over them is not visibly. I don't mean
Well, invisibly, I suppose, there is always an eye, certainly merit increases probably have some relationship to the practical output.
I mean certainly all their all the work on semiconductors which they did was the best in this country. But they certainly recognized
Well, they set up a semiconductor group because they recognized its value. And they hired certain people like Bardeen and cleverly put him in the same laboratory with the people who were working on semiconductors. But I don't think that while the group was studying semiconductors they had any interference.
No, that's right. And I didn't wish to imply interference. I would say well I don't know that they have had any groups which haven't succeeded, but now I think I heard a case with respect to Jansen noise radiation he was discouraged.
Oh, Jansky, apparently I think he was discouraged. But I don't know too much about him.
But I think is an ideal way that a laboratory should be run where they have everyone working whether it's applied or what you call basic and I dislike those terms because those applied guys the people who knew what their applied objective sure worked on basic phenomena.
In 1953, you participated in a symposium on exchange interactions chaired by Kittel.
Slater was there.
Slater was there, Stoner and Van Vleck.
Stoner was there, that's right.
And I wonder whether you have any special recollections about that symposium.
I think that was a very heated. This is where I think probable that Slater and I clashed on this matter.
Ferromagnetism, right. Any other recollections about this? What about the other people how did they divide in this controversy or were you and Slater the main antagonists?
Well, I had a student, Hikis, who naturally backed me up.
We're getting close
You want some sort of personal tidbits in there.
If you have some that come to mind.
And you also wanted to know the environment of industrial laboratories. Having brought Hikis up, I'd like to tell you a story there. He was a terrific, he got his Ph.D. at Harvard at Chicago with me and came to Westinghouse. He wanted to have an opportunity to get into management in the company. Research people have a bad reputation, it's not a good reputation as far as practical things are concerned. So he wasn't not able to obtain a position, and at my advice he left and joined Motorola within half a year he was sent to Europe in charge of their European operation and then came back to Motorola and was made a group vice-president. So that this is an example of how a corporation is apt to unjustly be suspicious of people coming from a research laboratory.
Let's see, is there anything special to say about the classical theory of the temperature dependence of magnetic anisotropy energy or should we
Oh yes, there is of interest here, it's related to this diagram on the board of interactions. With increase, if you're looking for a time, do you have a time you have to be?
I think I have at least another half hour.
There is something that comes up here. The strength of the anisotropic coupling involves an integral of a Bessel function that has ups and downs and the spin distribution the higher the spin distribution that spreads out and the smaller that integral becomes. In science it's interesting how you can sort of smell problems when you have a certain background, when you don't that background, you don't smell it. And this was a good example.
The one paper in this period by d band and mixed valency semiconductors, how did you get into that?
Oh, this was the
It seemed out of the mainstream of the work you were doing.
Oh, okay I had an idea which I thought was a great idea but it didn't work out in practice. The idea is the following: it's been known for a long time that there is a relation between electrical conductivity and the thermoelectric effect.
Sure, the Wideman-Franz.
And you can make this coupling surprising large. For instance, you have an n junction a p junction and two plates. You firstly you allow a current to flow and measure the thermal conduction. Then you put a slice here so a current cannot flow and the thermoconductivity can be reduced by more than a half. There's a big coupling not just small. Now one way of getting a large coupling is as follows. You know, I spoke about when you have a large interstitial atom displaced you are lowering the local shear moduli so you have an increase in entropy local entropy which means you have a sort of a … there. And you have this strained if you have another valency if both of the ions are double valency and you have a triple valency so when that moves from one atom to another by jumping electrons I felt this nugget of heat would move along and so give you a large thermoelastic constant. If we could have increased that coupling by a factor of three, we would have done away with the modern methods of power generation, but doggone it, we couldn't do it.
It didn't work. Let's see, the last three papers I have here are very general. The impact of magnetism on metallurgy —
That's a review, sure.
Metallurgical designing for strain. And thermoelectricity impact. I don't know if you want to add too much. Here they're very clear. There was one question about here you mention Joffe —
I think I give this coupling speak of this coupling that I was trying to do. I didn't know at that time that it couldn't work.
You point out Professor Joffe's book. I was wondering whether that was something that was widely read at that time, the book on semiconductor elements.
Well, we certainly had it in our library at that time, so in that respect.
Well, then you go on to Texas A and M.
And in 1968 to Carnegie Melon. You've changed … work slightly.
Sure. As a matter of fact, I consciously did not want to start work at Westinghouse that I had done in Chicago. And yes, here, it's not solid state, it's not liquid, it's not gaseous, it's two-phase mixture, but it's then the difference between isothermal and adiabatic. Do you mind 10 minutes, not more.
I should call her and make I have to one errand before I can meet her I'm just afraid that because (end of tape)
This is our water-phase diagram. Entropy, temperature. Liquid, gas. Two-phase. In the customary method of getting power using water system, you come across here isothermally at some consistent ... namely, we're going to drop down without any change in entropy. Now, how do you do that? How do you lower the temperature without putting heat away from the system. If you have a bubble at the pressure that we have here, about half a pound per square inch and lower the pressure, the pressure characteristic of the … 2/10 of a pound per square inch. This will expand and confined to … the energy the work which you can get out is the area under this in this and that work corresponds to a rise of height. The interesting physics comes in. Suppose we start and expand in volume by a thousand ... of what were close-packed bubbles before now become close-packed cells they have if they sort of close-pack face-centered closed pack you would obtain dodecahedra. The physics is fascinating. If we did some tetragonal cells Cyril Smith will tell you pure … form must be stable. The properties … they have two parts they want to go to the surface because they have a … once you have a two-phase system you … stable in the sense that it won't just mechanically fly apart. However, a number of anomalous … firstly, the pressure is … so a more … there's a counteracting step, however, as you and a cell is expanding the walls are expanding … well would be fine if there wasn't gravity, but of course gravity takes everything would work fine if you wouldn't have to do this with such a low concentration … so if … these … viable now these were what I mentioned these was … the radius of curvature is of the order of 10-2 the wall thicknesses are of the order of a micron. Now we don't want these walls must be held up against gravity so if this is a vertical it can only be held up if the concentration is higher down here than up here. Now interesting ate lower concentration, the sideways pressure is proportional to and is equal to kT times the surface concentration, that is they behave as a perfect gas. So we have a problem here where the laws of physics are extremely simple, perfect gas, and the surface concentration is proportional to the volume concentration, concentration of mass, everything is known. Well we just have to design things so that they hold together, and we have equipment … demonstrating this we have a three-story chemical engineering laboratory we have a pretty good … it's interesting that the physics of this kind of a system have never really been worked upon. Cyril Smith has written, see, we are interested in … which last for only a second and then they're destroyed, but nothing is stable on a long-term basis, so that's the.
Very interesting. Fascinating. Well, I'd better pack up.
Could I tell you, do you know
I just need to transmit some material to somebody who's in Singleton, so there's no problem so I just …