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Oral History Transcript — Dr. David Dennison

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Interview with Dr. David Dennison
By Thomas S. Kuhn
In Ann Arbor, MI
January 27, 1964

open tab View abstract

David Dennison; January 27, 1964

ABSTRACT: Born in Oberlin in 1900. In 1902, moves to Ann Arbor. Discusses fatherís career in the classics, his interest in science, and his sabbatical in Rome in 1907 and 1908. Dennisonís early interest in wheels and mechanical things mentioned. Moves with family to Swarthmore in 1910. Describes science sessions and experiments with Matos, the minister of the Episcopal Church. Discusses his high school chemistry and mathematics studies. Receives guidance in his scientific interests from university staff, particularly, Dr. John A. Miller, professor of astronomy. Devises phonograph needles, visits a neighborís amateur laboratory. Attends Swarthmore. Participates in the Student Army Training Corps. Majors in mathematics. Describes his first physics course, work with microscopes making biological cultures, course in intermediate mechanics, and electrical engineering experiments under Dr. Lewis Fussel. Works for the General Electric Company during the summer of 1920. Mentions W.R. Whitney, Langmuir, A.W. Hull, and S. Dushman, W.D. Coolidge at GE. Bohr atom is described in his course in modern physics. Recalls his first impression of the Bohr atom. General Electric research helping Langmuir calculate atoms and molecules, calculating the integral of pdq for mechanical set-ups. Describes Langmuir. Discusses his decision to enter into theoretical, rather than experimental, physics.

Transcript

Session I | Session II | Session III

Dennison:

Ö Well, first of all, just the historical details of where I spent my early life. I was born in Oberlin in 1900. When I was two years old the family moved back here to Ann Arbor.

Kuhn:

The family was actually an old Michigan family, was it?

Dennison:

Yes, yes. My father was born here. As you can tell from that and from the later time at Swarthmore, this was an academic family. My father was a professor of Latin and Greek, I think perhaps more interested in the archeological end than he was in the language end as such. I think he was himself somewhat interested in scientific things, but of course all his training, his life, was really in the classics.

Kuhn:

When you say you think he was also interested in scientific things, I wonder in what ways this came out.

Dennison:

Well, I think first of all just my motherís statement that they went to the Worldís Fair in Chicago in the 90ís, was it? He spent most of his time in the hall of machinery there. And the fact that in the archeological work, in making measurements, while he had very crude instruments, measuring tapes and so on, there was an indication that he was a little careful about his measurements and was thinking about this kind of thing. Unfortunately he died in 1917. Incidentally, you can always tell my age at each point because, being born in 1900, the last two figures of the year are always my age. This was the time, of course, when I was just emerging in my own thought and my intellectual development, and so it was very sad, really, because he would have been just at the point of being able to appreciate what I was thinking, and I could appreciate what I was thinking, and I could appreciate what he was thinking. Not that we didnít have many conversations before then, but I can see now that we were at the point where we would have bad much more.

Well, again, just to go back a little bit in the history, I then grew up here in Ann Arbor. I think it was my 7th or 8th year, probably my 7th, he had a sabbatical which we spent in Rome. This was a very lonesome year for me, in 1907-08. There was no possibility really of playing with ordinary children in Rome. It was only really kids with kid gloves and canes and things like that. There were childrenís parties, but this was about the way it went. So it was a very lonesome kind of year. I was left pretty much to myself. I think I can see, when I think back, that at that time I was fascinated with moving things, with wheels and things of this sort. I can recall for example using threads and bent pins; I was making them spin and looking at them and admiring them. This, I would say, was probably the first definite kind of beginning of my interest in mechanical things which led me then into physics. After that year we were back in Ann Arbor here, and in 1910 we moved to Swarthmore, again a relatively lonesome sort of experience for me. I was not very good about picking up friends. There was this business of getting a few here and then transferring to a new place. It was that kind of thing which Iím sure led to a rather quiet, shy person with a good deal of introspection.

At Swarthmore I met by accident the minister of the Episcopal Church. He must have been of Spanish descent; he looked that way. His name was Matos, M-a-t-o-s. He was a very remarkable guy. He was interested in science; he was interested in practically everything. He was first an amateur astronomer and he had an observing program with the college observatory. You see, they have a very good telescope, this Sproul 24 inch telescope; and he took some of the observing times there. He had a marvelous study -- terrific disorder -- walls lined with books, a three-inch telescope, a static machine, all kinds of scientific tricks. What he did was to invite boys, not necessarily in his church, anyone, to come two afternoons a week, Wednesdays and Saturdays. There were usually three or four or maybe 8 boys that would congregate here, and he would at times show these various tricks and also a good deal of mathematics. I think I was very much inspired and pointed towards scientific things. I mean, he was interested in every intellectual thing, but probably more so in scientific things.

Kuhn:

Were these afternoon sessions principally given to the sciences, or did he range over the whole --?

Dennison:

It was anything. It just depended on the boys who were there and their interests. And there wasnít any program; it was just that when you would come to see, if you hadnít seen the electrostatic machine, he would run the thing. If you had seen it, and you wanted to run the thing, that was all right, too. He had, oh, half a dozen, Encyclopedia Britannicas, various editions, you know. He would do things; he would make little pictures with cobalt chloride that is blue when itís dry and red when itís moist. One of his tricks, for example, was using a pan of water and showing us germs; the germs were always created by little flakes of gum camphor. Youíve probably seen them, they wiggle on the surface. They look just like germs, and then you can kill them by simply running your hand in your hair to get a little grease and then put it in, and they all die, like that. It changes the surface tension of the water. [Chuckles] It was just dozens of these tricks, and they made a great impression on me. He also loaned me a little water motor with a dynamo on it, and I played a lot with that. Well, this is mainly pre-high school and high school. In high school I had chemistry, not physics. It was very badly taught. I got almost nothing out of it except the interest to collect some chemicals and Iím afraid to do the more gaudy sort of experiments, and also the more dangerous ones. When I think of some of the things I did! Making thermite and burning holes through -- setting it up and thinking it was going to stop -- and it just dropped right on through when it went off. My mother was very patient about these things, and also I suppose I didnít perhaps display them too much, either. Also at this time perhaps I had a little bit of cooperation from the college physics department. It was about this time that my father died. Oh, I might say that in high school I donít think I was particularly inspired by any of the teaching except perhaps mathematics. There was a very good mathematician there, and I was very much fascinated with that.

Kuhn:

How far did you actually go in mathematics?

Dennison:

Very little. Just algebra and geometry. You see, around 1912, or 13, or 14, one didnít go very far.

Kuhn:

Not even trigonometry, though?

Dennison:

Not even trigonometry.

Kuhn:

Did you read in any of these subjects outside?

Dennison:

Mr. Matos told me a bit about trigonometry, and logarithms, and a few things of this sort; but I didnít really use them, I donít believe. Mainly I think geometry and things of this kind, and algebra, I thought that was fine. Well, it was just about the time that my father died that I became interested both in chemistry and astronomy and, with Mr. Matosí help made a very small and inconvenient telescope. After my fatherís death, the remainder of that high school year, I think I began to get some help from the college people. One of my fatherís very close friends, Dr. [John A.] Miller, was the professor of astronomy. He allowed me to use the student telescope, a six inch telescope and the dark room associated with it, and I began to make lots of observations. This went on during the first year or so of college, and then I also began making regular professional observations with the 24 inch -- it was part of their parallax program -- and took hundreds of plates and also later went through the process of reducing it to actually -- well I did the measurements on the plates and then also did find the parallax of one or two stars. Iím sure I didnít know what was going on in detail. I knew the general thing, but it was, so to say, a regular program that one followed.

Kuhn:

Before we get too far into your actual career at college, Iíd like still to stay back with your school period for a little bit longer. Iíd be interested in knowing what other sorts of interests, competing or not competing, you had. I gather from what you say that you didnít have very many friends, that you were a quiet, somewhat reserved boy. What did you do with your time?

Dennison:

Well, oh, I did have some friends, all right, and I think we were interested in various scientific things. One of my friends had a phonograph. We played a good deal with that, trying to devise better needles. You remember the thing was in those days that needles made too much noise, and in trying to find the perfect sort of needle we manufactured all kinds of things to do this. Also, there was a boy somewhat younger than myself, two or three years younger, again who was very quiet and introspective, who lived in a neighboring town. His family was very interested to have me be with this boy. Their family was much richer than ours, and they had a good many things. For example, during the high school period, he had a machine shop with a metal lathe and drill presses and things of this sort, and I was very much fascinated with playing with these things and making various things. Oh, they were kind of scientific things. I borrowed enough material somehow or other, through the college, I think, I had on loan a very ancient spectrometer, and played with this. Itís strange how different people have had influences, and that these people existed!

There was a man who was I think a technician in the (Coleman) Mustard Company in Philadelphia. He lived a few streets away, and he was one of these amateur scientists. He was, one of the first people who had learned how to make replica gratings, and he had made a good many of them. I only went there, I think, one single afternoon, but he showed me his laboratory and the spectrum of a carbon arc with one of these gratings, and he gave me one of these small gratings, which I played with for years and years, making spectrometers and so on. And he also had something which was very trivial, but it made a tremendous impression on me, a double pendulum. He had made it with a pen which would actually work. He made several of these pictures and gave me some, and I still have one or two of them today. I have myself made one or two of these double pendulums since just because theyíre fascinating. They make these very beautiful scroll pictures you know. You can see that Iím attracted to scientific things, but also perhaps a little to the gaudy things at times. This was one of them. This single afternoon, as I said, made a tremendous impression on me. I can see every detail -- well, here are these people that exist. Now I actually went to Swarthmore because my father had died. Of course thereís always the financial question, and they gave me a tuition scholarship or something of the sort, and my mother stayed on and eventually became one of the housemothers in one of the girlsí dormitories. This was 1917, the beginning of the war, and of the Student Army Training Corps. Like everyone else, I was a member of this. Now, let me see, here is something wrong. When did we actually enter the war? It was in 1918.

Kuhn:

Ď18 -- Ď18 that we entered the war, ja.

Dennison:

Then my first year was before this, because my father died in March of 1917. Then in the fall of 1918 I went into the Student Army Training Corps. I was very resentful of it, not in the sense of anything connected with the war, but Iím one of the people who has a dislike of being so-to-say a number.

Kuhn:

As a matter of fact I think Iím wrong, it wasnít Ď18; Ď18 was the end of the war, Nov. Ď18.

Dennison:

Thatís right, that was the end of the war, but actually the Student Army Training Corps was only in effect for a couple of monthsÖ I disliked being taken care of. My roommate, a very able guy who went into science, (McCullough) had just the reverse viewpoint. He the fact that he was taken care of, that he had no responsibilities, that everything was arranged for him. But I didnít like it and was therefore very glad when it was over. I majored in mathematics; it was easy for me. As I look back now, the first two years of college I learned a great deal. I learned from a mathematician, it was college algebra -- it just opened my eyes to a lot of things that I had never thought of before -- also calculus, which I actually didnít get until my sophomore year. The kids now get it before high school! Thatís the way it was. And trigonometry too, at the same general time. It was very elementary mathematics, but it made a great impression on me, and it was also moderately -- I mean, I had to work. By sometime I guess in my junior year, I learned the trick of studying, and in particular of being able to pass any examination. From that time on I guess in everything I got straight Aís, and I didnít learn very much. The first two years when I had to work, and didnít know the trick of how to pass examinations, I learned something, but then later I didnít learn nearly as much.

Kuhn:

Were you in these years in high school, a particularly good student? Were you one of the people pointed to as someone who would go far in his chosen field?

Dennison:

I think the people who knew me, who took the bother to look at me a little carefully were of this opinion. That is to say, the mathematics man in high school, and, I think, of course most of the people in college, because then I began turning in these perfect records. My grades in high school would have been on the average very good, but by no means perfect. The average person there would not have thought that I was going to be particularly good. Itís sort of amusing -- I think it was my sophomore year, when I had the first course in physics that I had ever had, general physics. I neither understood it, nor cared to understand it, nor did well in it. I think I got a C, which was as low a grade as I got in any course in college. The man who taught it was a replacement for that year. He was a very good sort of person, but not my type. I am not one of these really meticulous people. Just to illustrate -- in handing back my laboratory reports I can remember his writing on them, ďAnything that is worth doing is worth doing well.Ē [Laughter] You can see what sort of person he was, and also see what my reaction was. But it really is true, and I think that for example of this business of acceleration, centimeters per second per second -- what the hell! What did per second per second mean? I hadnít the faintest idea what it was and really, as I say, didnít care. And yet all the time I was surely a physicist. My real interests, my attractions, were mathematics and physics, no question about it.

Kuhn:

But at this period, itís perfectly clear as you tell it that this was the right direction for you to be going, but you canít yet have been thinking of yourself as somebody who was going to be a physicist.

Dennison:

No, I donít think so. Perhaps I was moderately sure that I would be going into academic work. Why? I suppose the same reason that actuates most children -- they admire their parents. It seemed like a good and interesting life; and the fact that I was just interested in intellectual things. About the time of my fatherís death I got my mother to buy a cheaper version of the Encyclopedia Britannica -- they had just come out then. And I simply read in this -- all the scientific things. This was my source book you see. And it had a lot of influence. I must have felt fairly sure that I would go into academic work.

Kuhn:

Did you at that point read, say, geology and biology as well as physics, mathematics and astronomy?

Dennison:

I didnít happen to touch on geology. However, my interest in the apparatus of physics of course led me into microscopes. Here again, I got the loan of a very ancient one from the college -- this was during my first year of college, at the end of my high school time. The man in biology, of course very sympathetic with us after my fatherís death, wanted to be of a little help, and got me to employ my skill with microscopes, and also in taking pictures -- I was pretty good at taking pictures too -- to make up for him a series of slides in the development of the embryo. He had the prepared slides, and I made lantern slides out of them by taking pictures through a microscope. In this way I got to be interested in biology, but really only in so-to-say the Ďintellectualí approach to it. I was not, and probably never would be, a Ďjuicyí biologist. [Chuckles] But I made cultures of things -- this is as far as I went. The other thing besides this, probably back in the back of my head was the notion that I would get into academic work, but also the fact that my father had spent also three years in Europe. This was after his under graduate training, which was here at the University of Michigan, and then he went to Europe to obtain his doctorís degree. It was quite clear that this period had had a tremendous influence on him and on my mother, and I think that I was very sure that this was something I was also going to do in completing my training.

Kuhn:

He was already married when he went there.

Dennison:

He was also already married when he went there. Sometimes I feel very, oh, I donít know, sad isnít the right word, but unhappy, when I see the sons of my colleagues all following so directly in their fatherís footsteps instead of thinking a little for themselves. Iím afraid perhaps I did the same thing; itís very natural. But it certainly is true. It isnít by chance that artists become artists; and so it goes. Well, the fact that I went into academic work was certainly not chance. The fact that it was science though, rather than classics, this was my turn of mind. And this, I think, was always definite from, oh, as far back as 7 or 8, when I think of what really interested me, steam engines and that sort of thing.

Kuhn:

Were you thinking at all about which science? Was mathematics a form of science from your point of view?

Dennison:

No, no. Well, had I really been thinking at during the late high school and early college, it would have been chemistry or astronomy.

Kuhn:

What about mathematics?

Dennison:

Mathematics was very interesting to me, and this was what I majored in; however the examples which seemed most beautiful to me were the ones from physics. So it was really that mathematics opened up my eyes to what there was in physics. We had for example a course in what we would call here intermediate mechanics, a very inadequate sort of thing Iím sure, that came in my junior year after I bad had this general course in physics. Then suddenly to see how one could integrate the equations of motion and get simple harmonic motion, something that kids now do you see way back certainly in their freshman year, but when this hit me, it was wonderful. It just opened my eyes to all the possible things one could do. So mathematics was one of the things that brought me into physics all right, but physics had the most beautiful examples. This is the way it went. I liked doing things with my hands experimentally, but I was no unduly clever with it, not unduly, but I was all right. Well, letís see, one more thing before we come to my coming back here for graduate work. There was a man in electrical engineering at Swarthmore, Dr. [Lewis] Fussel, F-u-s-s-e-l, [sic., should be Fussell] and he was very kind to me and I think very much impressed. I took his course in electrical engineering, and of course with a knowledge of mathematics I could hit it dead. I could beat all the other people in there without any difficulty. [Chuckles] They were mostly engineers and were a little hazy about what to do, you see.

He was very much impressed with this. Following this desire for doing things in physics, but also a little bit gaudy things, too, I did a number of things that he at least gave me space to do in his laboratory. One was to build quite a large Tesla coil. This appealed to me, I think probably from the gaudy side, you see. Well, I wanted to make one that would make a spark 6 feet long, and I did. It was quite a whack when it was all done. This was all [a matter of] going to Philadelphia to the portrait photographers and getting stacks and stacks of their old glass plates and soaking the gelatin off, you know, and making up condensers -- I made everything -- and a rotary spark gap. I wound this big cylinder for a fine big-spark Tesla coil. I did another thing which was also, Iím sure, just for gaudiness, but it interested me. This was taking the motor generator set they had, which was making, I think either 110 or 220 D. C. and was fitted with a circuit breaker and a switch, and short-circuiting it with a copper wire and throwing the switch. Of course two things would happen. The copper wire absolutely explodes, as you know; and the circuit-breaker goes out. Thereís no real damage to anything. I had quite a lot of fun doing this and noticing how, for example, while there was a tremendous brilliant flash, one could put a sheet of paper very close to it. What it would do was deposit metallic copper on the paper, but it wouldnít burn the paper because it happens too quickly.

Well, this was the sort of activity that I did. Dr. Fussell wanted to help me, and at this time the General Electric Company was having a sort of student employment in the research lab during the summer time. The first summer that I went up there was in 1920. It was between my junior and senior years. Dr. Fussell gave me the necessary introductions, but I had to go up to Schenectady for an interview and was interviewed, and they gave me a job for that summer. That was wonderful, that was also wonderful. That was, I think, the height of the beginning of this laboratory. [W. R.] Whitney was the director, and he was surely one of the first people who understood scientific management. He had a wonderful group, Langmuir and [A. W.] Hull and [S.] Dushman and [W. D.] Coolidge, these were the principal ones at that time. It was wonderful. Now, my junior year, we had quite a good man there, a good teacher, a better teacher than Iíd had before. He gave a course -- we would call it now modern physics -- in which he described the Bohr atom. As I remember, there were just two people in the course, my roommate and I. This was also in a sense the beginning of the kind of educational experiment that Swarthmore went into later. Swam was the president at that time, not Aydelotte; Aydelotte came just the year I left. But it was then carrying on a good many of this kind of experiment; and I had a number of courses where I was either the only one or maybe just with one other person in it.

Kuhn:

How did the Bohr atom strike you when you first heard about it?

Dennison:

I didnít know enough to know how wonderful it was.

Kuhn:

Did you know enough to know how odd it was?

Dennison:

Not really, no. No, I was not mature enough to really appreciate what the difficulties were.

Kuhn:

How did the man who taught you feel about it; I mean, was that it so far as he was concerned?

Dennison:

Well, he was giving me some of modern physics. That it was to be a really powerful sort of thing, I donít think he would have felt this way. It was, however, the latest development. He was interested, and he gave it with enthusiasm. The main thing was, I thought I knew it. I had hit it; I knew it. So when Whitney, I guess it was, asked various things about my interests, I said that I knew about the Bohr atom, I had been through this. So he first sicked me onto Langmuir. This was wonderful. Langmuir was in the middle of his calculations on atoms and molecules. Langmuir really didnít know anything about how it [the calculation] was to go. He had this magic formula of the integral of pdq, but he would have been perfectly willing to make any kind of orbits that either satisfied or didnít satisfy mechanics. At least thatís my impression. He made a great impression on me in a variety of ways.

Kuhn:

Was he, at this point, very clearly using what seemed to him a Bohr atom, in that it was a dynamical and no longer a static atom.

Dennison:

Yes, he was. Thatís right, and he was in the middle of making this kind of calculation, for example, calculations on helium and I donít remember which other ones, but helium, I think was the one that he was principally working on at that time.

Kuhn:

One of his models was one in which he put electrons at two ends of a diameter, and it oscillated back and forth.

Dennison:

It vas this kind of thing. He set me to calculating the integral of pdq for various mechanical set-ups. I would calculate on a desk calculator, not an electric, all day long. He would take the machine home with him at night, and he would do more at night than I did all day. Also, I would make mistakes. It was a question of getting a series of points, and one wanted to draw a good curve. One of the things I picked up from him at that time was that in doing this sort of work it pays to get one or two points that you know are right rather than to get half a dozen of which you doubt whether any of them are right. This one I picked up. Langmuir was always in a hurry, gave the impression that he had much more to do than he could do in his lifetime. He always pranced around. When heíd come in in the morning, he wouldnít say, ďGood morning;Ē he would just plunk down at his desk and start in. Well, this shocked me a little bit, I always said ďGood morningĒ to him, and after a bit this must have gotten under his skin because he started saying ďGood morningĒ to me, too, automatically. In spite of this hurry, he took me around the laboratory and showed me all the things that went on. I was quite astonished because I had heard about commercial secrecy and patents and things of this sort, and I said something to him that I was astonished that here Iíd just come and they showed me everything that went on. ďOh,Ē he said, ďthereís absolutely nothing to this secrecy business.Ē He said, ďOnce in a while youíll find a man who wonít tell you the details of what heís doing. He locks his room and wonít let you in.Ē He said, ďItís almost invariably true that he has nothing to hide, and thatís why heís trying to hide it.Ē [Laughs] Everything with Langmuir was completely open, and I was very much impressed by that. I calculated with him for quite a while until I decided, well, Iíd had about enough, so I began objecting a little bit to keeping on; and it was at that time, then, that he turned me over to Hull.

Kuhn:

ÖYou said you took your first physics course in your sophomore year and at this point although you knew you were going to be a scientist and knew the sorts of things that interested you, you probably didnít know you were going to be a physicist yet. I wondered at what point, that became clear, and I would ask you together with that, what you then took a career in physics to be. What was it that physicists did, at the point you decided to be a physicist?

Dennison:

Well, first of all, at what point did I formally, so to say, think I might go into physics. I remember talking with a professor of physics -- this was in my junior year -- a man by the name of [H. C.] Hayes, I believe.

Kuhn:

Was this the man who gave you the modern physics course?

Dennison:

Yes, he gave me the modern physics. Well, I guess I had about finished with chemistry; I had a feeling chemistry was not really interesting enough, was too applied. But I was still very much interested in astronomy, and I made the remark, ďAstronomy was the oldest science and the most fundamental in many ways.Ē He said, ďNo, this is not true; physics is really the one,Ē and that ďall these others are really just outgrowths from physics. Physics is the central one and then these others come off of it.Ē As I thought about that it seemed to me that it was really true, that all the things I was interested in, whether they were instrumentation or biology or astronomy or anything, they really were all centered about physics. I guess it was about then that that, plus the fact of Fussell sending me to General Electric and my seeing the physicists at work there, this probably did it. But what was physics? Just a beautiful intellectual business.

Kuhn:

Well, now, Iím fishing for one particular thing in asking that question, and this is sort of its relation to mathematics and the extent to which it was a purely experimental field. Obviously it was in this area that America had its own strongest work, and many people thought of physics as strictly an experimental field. The notion of theoretical physics as a field was not so old in Europe and was in some places, at least, nonexistent here. Some notion as to whether there was felt to be a conflict, a choice to be made, whether it was all one, and if all one, all experimental -- this sort of question is the one Iíd be particularly interested in having your reaction to.

Dennison:

Well, I can, if I jump ahead just a bit, maybe help you see some of the answer to it. The work that I did at General Electric during this summer and subsequent ones was partly experimental, but partly always the interpretation and I was undoubtedly more successful at interpretation and calculation than with the experimental part. When I came here, Professor Randall assumed that I would go on with the X-ray work and with experimental work; they had some X-ray work going. Now this is a conversation that Randall has quoted back to me; in fact, he did it about six months ago. I had forgotten it, but now that he brings it back I recognize that it is correct. It happened just this way. He asked me whether I was going into this. He assumed I was. I said oh, no, I didnít want to do that at all. He asked what I did want to do. I said I wanted to do theoretical physics. Now, this was very odd, because no one had ever done theoretical physics here. He asked me why, and I said it was because I thought it was the more difficult thing to do. [Laughs] This makes me blush now, but that was apparently my attitude, that if it was more difficult, therefore it was probably also more interesting if I could do it. And this is what I wanted then to do. Does this at all help answer the question?

Kuhn:

Yes, yes, indeed it does. It is not likely, if you said no, you wanted to do theoretical physics, that this is now the modern vocabulary for what you said then. I wonder really whether in your own mind, there were already two sorts of things, whether you may have said, for example, Ďproblems in which there was more mathematics,í Ö and less experimentation, or whether the notion of a theoretical versus an experimental physicist could have been in your mind, which it could have. But it would then be a question where you had gotten the notion of that sort of distinction which in some places in this country scarcely existed yet.

Dennison:

Well, I think it was from, perhaps, admiration for what I had picked up of Bohr theory. It was from Langmuir, who was a theorist, really, coupled with mathematics, I think I was quite definite that it was theoretical physics. Walter Colby, who was here, whom I also admired very much, was a theoretical physicist, although I could not have known him right at this time. This was right at the beginning of the time when I came. Incidentally my thesis was the first thesis in theoretical physics in this university -- as late as l924.

Kuhn:

You know Van Vleckís thesis was the first Harvard thesis in theoretical physics?

Dennison:

Yes, I imagine thatís right.

Kuhn:

Kemble got permission to do this, but then somebody else was doing relevant experimental work so he got some experiments in it, too, and Van Vleck was the first person.

Dennison:

Well, Randall was very uneasy about my doing it, but I was very definite in what I wanted to do, and there was just no putting me off. [Laughs] ÖI would just make the remark that I think that the reason that people went into physics at the time that I did were often somewhat different from the reasons for young men going into it now. This is one of the wonderful things that you have before you, this tremendous difference between what physics was, the spirit of it, the people that went into it, why they went into it, what their interests were, in the twenties and even thirties as compared with physics now. Now it is so closely mixed up with the economy of the country, with the military life and everything else, things that didnít exist in those days. Thereís a real point, I think, in trying to establish in some detail the atmosphere, the people, why they went into it. I hope you will also take people of the next generation, who came into it in the late forties and the fifties. Why did they come in? What was their background? What pushed them into it? Many of them are just the same type we are, but many are not; many have come in for different reasonsÖ This is almost a social science question rather than a historical question.

Kuhn:

Well, these are not totally distinct fieldsÖ There are in fact all sorts of directions in which one could spread from here, and a comparative study of scientific motivations, and sources of scientists in the forties and fifties would be a very important thing to do. What I would want to ask you -- and it may be a little hard because you are yourself right at the transition point in a sense -- is whether there arenít really perhaps three trends, three periods rather than two. It would seem likely to me that if one goes back to people who went into physics in this country perhaps ten years before you did, in a period when there wasnít any such thing as theoretical physics, the thing that is also clear with you, but clear in a more balanced way, of an interest in machines, in experiment, in fooling around with equipment, would have been the almost exclusive source of physicists. But I think if one takes people who entered physics ten or fifteen years after you did, which is still before there is a deep involvement with military policy and with economics, that a strong interest in mathematics and almost a distaste for experiment would also be a sort of person who went into the sciences, and who probably would not have gone into physics yet in your period. Then one sees the more recent stage what I would call the third stage; I would say the engineer is now a physicist, at least some engineers are physicists. You would have seen not only the present generation but also the generation which entered let us say at the time that I entered college in 1940, a group of people who really did not like going to lab at all, and who had not been attracted to physics in the first instance in any part because it was something where you dealt with equipment and used your hands.

Dennison:

Yes, I think that is probably right. Another very interesting speculation one often has: ĎWhat would I have been if I had been born five hundred years ago?í I think I would have been an artisan, a technician; this is probably what I would have ended up as with this interest in material and form and things of this sort. If I had been born when father was then probably it would have been something like archeology and classics, because if you remember in the last century this was one of the very exciting sorts of things, again having to do with deciphering, of anything. I have often thought, as you probably also know -- and have the same feeling, about the so-called scientific method. I think this is complete bunk. In intellectual field you use this business of looking and checking, and self-consistency.

Kuhn:

Did you do classical languages?

Dennison:

I did a certain amount of it. I am not a very good linguist though so it didnít take on very well.

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