[Thompson, 1973]
Thompson, 1973 (NRAO/AUI image)



NATIONAL RADIO ASTRONOMY OBSERVATORY ARCHIVES

Papers of Woodruff T. Sullivan III: Tapes Series

Interview with A. Richard Thompson
At VLA, Socorro, NM
1 May 1978
Interview time: 70 minutes
Originally transcribed by Pamela M. Jernegan (1979), retyped to digitize by Candice Waller (2016)

Note: The interview listed below was originally transcribed as part of Sullivan's research for his book, Cosmic Noise: A History of Early Radio Astronomy (Cambridge University Press, 2009). The original transcription was retyped to digitize in 2016, then reviewed, edited/corrected, and posted to the Web in 2016 by Ellen N. Bouton. Places where we are uncertain about what was said are indicated with parentheses and question mark (?).

We are grateful for the 2011 Herbert C. Pollock Award from Dudley Observatory which funded digitization of the original cassette tapes, and for a 2012 grant from American Institute of Physics, Center for the History of Physics, which funded the work of posting these interviews to the Web. Please bear in mind that: 1) This material is a transcript of the spoken word rather than a literary product; 2) An interview must be read with the awareness that different people's memories about an event will often differ, and that memories can change with time for many reasons including subsequent experiences, interactions with others, and one's feelings about an event.

Click start to listen to the audio for tape 103B of the 1978 interview.

Begin Tape 103B

Sullivan

This is talking to Dick Thompson at the VLA in Socorro, New Mexico, on 1st May 1978. Can you tell me what your educational background was and when you first came into contact with radio astronomy?

Thompson

All right. I went to grammar school in England, it was (?) Grammar School, and from there I got a state scholarship to Manchester University. I took physics, which I was interested in, and the physics department at Manchester was running Jodrell Bank, of course, and I got interested in that, and during my first summer as an undergraduate, I went out to Jodrell and was a summer student there. That would be the summer of 1950. I mainly worked there helping one of the guys who was doing experiments on meteor radar, it was the radiant experiment.

Sullivan

What was his name?

Thompson

Gee, let me think. I have difficulty recalling it. Heís not in radio astronomy now; he left and, I think he went into electronic industry or something like that. I remember spending a couple of days in the summer helping Hanbury Brown and Hazard move the tilting mast of the 280 foot zenith -

Sullivan

To a different declination?

Thompson

Yes, to a different declination. Thatís right. But mainly I was working with the meteor people. Then, the following summer, I wasnít at Jodrell. The summer after that, which was the summer I graduated with a Bachelorís degree, I was there again. And, letís see, what was I doing that second summer as a graduate student? I canít remember whether I was working with Jennison or Hanbury Brown or who. Well, never mind, thatís not important. Then I decided Iíd like to do a Ph.D. and do work in radio astronomy. So I went to Jodrell and three of us went from the physics department that year. There was Matthew Dagg, myself, and Colin Gill. Mathew worked with Alan Maxwell. They had an experiment where they were following Cygnus or Cassiopeia to measure ionospheric scintillations. Dagg, after he got his Ph.D., went to Cambridge and took a course in soil physics and I think heís now director of a research station in Africa. Gill did an experiment with, not R.D. Davies, the other Davies, John Davies.

Sullivan

J. G. Davies.

Thompson

J. G. Davies, yes. That was a meteor experiment in which they had three stations; I think they transmitted only from Jodrell, but there were three receiving stations. This allowed one to pinpoint an orbit and get an orbit -

Sullivan

Different Doppler shifts.

Thompson

Thatís right, but they could get both, the precise orbit which you canít do by just looking at it with transmitting a receiver from the same place. And this was to see if there were any meteors with hyperbolic orbits. They did that experiment, and Gill got his Ph.D. and, I think he went into one of the British government agencies. Iím not sure which. And then I joined Hanbury Brown who, at that time, was thinking about making an interferometer with an antenna, a movable antenna, using the 218 foot dish with a tilting mast as being the main antenna and the dish was implemented for 158 megahertz which was a fairly high frequency in those days. And we made an interferometer -

Sullivan

Before you go on, let me just ask how it was determined that you would join him, were you just assigned to that group or did you have a choice?

Thompson

Well, I remember Lovell telling me that there were three possibilities. Three people working there at the time who wanted particular, who wanted graduate students to join them. And of the three of us going Ė Gill and Dagg and I Ė we settled it between ourselves. I think my preference was to join Hanbury, though I did wonder about doing the meteors. Gill, I think, said heíd just as soon do the meteors and Dagg did the other one and thatís the way it worked out Ė kind of by mutual agreement.

Sullivan

Okay. Now, Hanbury at this time had not done any interferometry, or is that true Ė was he already working on the intensity interferometer at that time?

Thompson

He had given the idea of the radio version of the intensity interferometer to Jennison and Das Gupta and they made it; and about that summer, letís see -

Sullivan

That would be 50 -

Thompson

1952, the summer of 1952. Jennison and Das Gupta were about to make their first measurements and with the radio intensity interferometer. The interferometer that we were going to build was going to a regular interferometer with a cable or radio link; we made a fairly transportable antenna. Actually, I made most of it myself out of two-by-fours bolted together with bolts and it had four frame sections, each of which had, I think (?)

Sullivan

(?)

Thompson

(?) but it had four forward guide poles on each frame section, and the frames stood side-by-side and then a single screen of chicken wire as a ground plate went underneath the layer of dipoles.

Sullivan

And this all folded up nicely to be put on the back of a truck?

Thompson

Yes, pretty much. It came into, the four frames took down, and I think it was possible, Iíve forgotten if we moved them as they were or whether we took the legs off, but one way or the other we moved them fairly easily. The interferometer was made in such a way that the master local oscillator was at the remote station so that the LO and the IF were going down the same way from the remote station to the home station down the cable which made it a little bit easier to make. And then we separated the signals at the home station, which was a hut at Jodrell Bank, which was called the Park Royale. I donít know if you knew about that.

Sullivan

The Park Royale.

Thompson

Did you ever know about that?

Sullivan

No, Iíd never heard of that.

Thompson

Oh, well, apparently in the early days of Jodrell Bank, they had a lot of trailers and one of them had to work Park Royale and that was a part of London, and this trailer was an old military trailer. It had been built by a company there, but it got to be known as the Park Royale trailer and when they replaced it with a building, they kept calling it the Park Royale Building. Well, the other building was the Moon Hut and the -

Sullivan

The Moon Hut was for lunar radar?

Thompson

Lunar radar. There was a meteor radiant hut, there was the, Iíve forgotten the names of the other, but it doesnít really matter. Okay, we separated the signals there and used, we separated the IF coming in from the remote station from the LO signal, which was, I think was a ten megahertz crystal which we multiplied up to 150 to be with the incoming signal at 158. Something like that, and then we beat down to a similar IF the signals coming in from the 212, the 218 foot diameter antenna, and the output went into a chart recorder. When we got to long spacings with that system, we -

Sullivan

You successfully moved out, I guess, going further and further?

Thompson

Yes, thatís right. Well, let me go back. At the time, Hanbury Brown had produced a catalogue of radio sources at 158 megahertz, and comparing this with the catalogue which Ryle had produced, a certain number of sources which Hanbury found near the galactic plane. These, of course, were found with the same antenna, 218 foot, but of course, in a single dish mode.

Sullivan

Right.

Thompson

The ones near the galactic plane were not in Ryleís survey. Now, it turned out that most of the ones near the galactic plane were large supernova remnants, which were half a degree in size upwards almost to the beam width of the antenna, and we found that it was very difficult to get our antennas close enough together to pick up the big ones. They were almost fully, well, they were resolved to many 50% or so, even when we had the two antennas sitting right side-by-side. With the rest of the sources, we had absolutely the opposite problem. We couldnít go far enough to resolve them. We ended up by taking the antenna out to the Cat and Fiddle Hill, not a hill, a mountain, near (Darbisher?) which was a line-of-sight from Jodrell Bank and that was the longest spacing we used. I was there about three and a half years at Jodrell.

Sullivan

How long was that?

Thompson

Well, let me see. If I may consult - thereís an Observatory paper which you probably have the -

Sullivan

The one in 1957 with -

Thompson

Morris, Palmer, and Thompson.

Sullivan

Right.

Thompson

Okay, and it was 10,600 wavelengths at -

Sullivan

2 meters, roughly?

Thompson

Yes, at 158 megahertz, so you could figure that out. I think actually we did -

Sullivan

About 20 kilometers then.

Thompson

I donít think we said exactly what it was in miles or kilometers.

Sullivan

Thatís all right, its roughly 20 kilometers. What Iím wondering, did you make a big jump out to this 20 kilometers from your previous baseline?

Thompson

No. We went up three or four places, three or four intermediates. Let me give you again, what they are in wavelengths. (pages turning)

Sullivan

It was a successive effort to try to resolve these things?

Thompson

Thatís right. Weíd gone to 56 wavelengths, I guess, when the antennas were almost close together, then 480, 630, 980, 2,060, 6,700, and 10,600. So there was an attempt to go roughly in factors of two or so depending on where there was a convenient site to put the antenna where somebody friendly would let us plug in to their electric power supply.

Sullivan

Right. How long did it take you to set up and change stations?

Thompson

Oh, setting up would be a matter of a day or two days, then you see, we observed only at meridian transit. We would tilt the antenna so that it would be at the appropriate declination then let the source go overhead. Weíd probably stay three or four weeks by the time we got good records and things.

Sullivan

So you were - And were these baselines all roughly east-west?

Thompson

No.

Sullivan

No?

Thompson

Here again, just a moment, I -

Sullivan

Well, in any case, if you were observing at meridian, youíre only getting the east-west structure.

Thompson

No, youíre getting the structure with regard to whatever the baseline is.

Sullivan

No, but only in east-west direction though.

Thompson

Well, if the antennas are separated on an east-west line, then you only get the east-west component of the structure. But it the antennas are at some other angle, Ö

Sullivan

Thatís what Iím trying to get at Ė were you worried about that effect or were you just - the possibility of asymmetric sources.

Thompson

At that time, well, that was kind of a secondary consideration, and no, essentially, we werenít. What we were trying to do was see what we could resolve. You see, at that time, Cygnus and Cassiopeia had been resolved with the intensity, the radio version intensity interferometer, and we were just trying to push things in the same direction for some of the weaker sources. Now at the same time, Mills had an interferometer in Australia which was a radio link device and it went out to a few kilometers and I think it worked at a somewhat lower signal frequency, either 80 or 120 megahertz.

Sullivan

I think youíre right Ė I think it was around 78 or something.

Thompson

Okay, and he was kind of the competitor in the game at that time. We eventually went further than he did and for a while we held the record for long baseline interferometry. Well, the Jodrell Bank and the Cat and Fiddle was the record for long baseline interferometry for a while. I might mention that in this earlier group of sources that we looked at, the ones which we found it difficult to resolve, one of them was one that Hanbury Brown used to call the ďfive-hour sourceĒ because it had a right ascension of almost 5 hours, it was about 4 hours and 50-something minutes. And Minkowski visited Jodrell and we talked to him about it -

Sullivan

What year would this be, roughly? Would this be at the Jodrell Bank meeting, perhaps, in Ď55?

Thompson

Yes, I think it probably was, yes. We got from him a copy of one of the 48-inch Schmidt plates which had a vague outline of this source on it, and I remember we wrote a little note for Nature and we kind of copied the outline of that source. That was one of the first things youíll have on there for me.

Sullivan

ďLarge Angular Radio Sources Near the Galactic Plane?Ē

Thompson

ďGalactic Sources of Large Angular DiameterĒ is the name of it.

Sullivan

Right, in Nature.

Thompson

Yes, in Nature.

Sullivan

In 1954, but that would be before, if Minkowski had visited you then in 1955, that would be -

Thompson

Maybe Iíve got it wrong. That same year, 1952 I think, Hanbury had been to the United States and he talked with Baade and Minkowski and I remember him coming back and telling us about the optical identifications of these early sources.

Sullivan

Right, Cygnus and Cas.

Thompson

And it could have been that it was a result of correspondence, subsequent correspondence, that Minkowski sent us this photograph.

Sullivan

What was the photograph of? Which source? This five-hour source?

Thompson

Thatís right.

Sullivan

And what does this turn out to be in modern day terms?

Thompson

Well, to tell you the truth, -

Sullivan

Itís a supernova remnant, I guess.

Thompson

Yes. And itís centered on the star, Alpha Aurigae.

Sullivan

Oh yes.

Thompson

No, wait a minute, itís not. Its centered on BD46°, 949.

Sullivan

Itís in the constellation of Aurigae.

Thompson

Yes, itís near Aurigae. Itís at about declination between 46° and 47° and right ascension about 4 hours and 58 minutes.

Sullivan

Okay, Iíll have to check that out. I remember this, though, this was a supernova remnant that was studied often in the fifties.

Thompson

I think that what happened was that, as far as I remember meeting, Minkowski, he did come over later for that particular meeting, the 1955 meeting, and we saw him again then. That was kind of an interesting meeting, we were all at -

Sullivan

Well, since you brought it up then before I forget, can you tell me why was it an interesting meeting?

Thompson

Well, for me, because it was the first time Iíd been to an international meeting. And there were all of these important people, like Minkowski and Greenstein and Baade and so forth, who were the great men who one had heard of. And one had an opportunity to see some of them and meet some of them. I remember Fred Haddock was there and talking about some measurements heíd done at 10cm. which was just an incredibly short wavelength in those days. Those were done with the old Naval Observatory dish; that was when he was with the Naval Observatory.

Sullivan

NRL.

Thompson

I beg your pardon, NRL. Naval Research Lab, thatís right. I also remember at that meeting, that, I think, it was Minkowski and Greenstein wrote a paper on some ideas they had for mechanisms of radio emission in which they were trying to get the spectrum from some kind of a mixture of thermal sources in a partly optically thick plasma.

Sullivan

Youíre right.

Thompson

And I remember that after that there was a paper by, I suppose, maybe it was Shlovsky or one of his colleagues. If it wasnít Shlovsky, it was another Russian who always used to come to meetings in those early days and read papers for his colleagues. Iíve forgotten what his name was. Anyhow, after it, I remember -

Sullivan

Proposing synchrotron radiation.

Thompson

Yes, proposing synchrotron radiation. Thatís right, I remember Minkowski getting up and saying that, ďI think we should withdraw our paper, donít you, Jesse?Ē And Jesse got up and said, ďYes.Ē

Sullivan

I see.

Thompson

It seemed kind of interesting that these guys were so willing to -

Sullivan

As soon as they heard about this it was clear then that this was superior?

Thompson

Yes, it was much superior, and I was kind of impressed by that.

Sullivan

Thatís interesting, Iíve never heard that story before. Well, who else? What about the Australians? Youíd never met any of them before.

Thompson

No, thatís right. Mills and Christiansen and they were interested, Mills was interested, in seeing our interferometer. Ryle was there. I guess that Paul Wild was there Ė I met him subsequently a number of times.

Sullivan

Yes, he was, I just interviewed him. Also, Joe Pawsey was there.

Thompson

Ah, thatís right. And Bolton was there. And Bolton, at that time, was talking about getting some dishes going in California, which eventually, of course, he did.

Sullivan

What about, you mentioned that Ryle was there Ė is this the implication that you hadnít had much contact with Cambridge Ė it took an international meeting to get contact between the two groups?

Thompson

No, there was some contact, but it, but not a lot. I hadnít met him before. Hanbury knew him and they were on good terms, but I think thereíd always been a little bit of question as to whether pencil beams or interferometers were the things used for sky surveys and Ryle using the interferometer and Hanbury using the pencil beam of the 280 foot dish. I donít know, Ryle was very interested when we toldÖ we were just beginning to get these results I think at that time, about the Ė no, maybe we had already resolved out the big sources and we knew the answer about why Ryle couldnít see them. That seemed like an interesting step forward, and then we were going to go on and press on and see whether these other sources were of the nature of Cygnus and Cassiopeia, which, of course, (?) resolved out fairly quickly and we thought weíd found out that they didnít.

Sullivan

So Ryle was willing to accept that there was a class of sources that his interferometer was not sensitive to.

Thompson

Yes, oh yes. He may have thought they werenít very important, I donít know, but sure, yes, he accepted that. Of course, he was interested in the cosmological aspects, thatís why I say he might not have thought they were very important at that time. Letís see, we were, had some very crude ideas in mind like the intensities of some of these sources suggested they might be objects like Cygnus, but ten times as far away. Therefore, the angular diameter might be on the order of one tenth that of Cygnus, and we were getting down to a few arc seconds. We were beginning to hit that, but really, I left before really we got much further with that experiment. And Barry (?) came along and joined Palmer on that.

Sullivan

Right.

Thompson

Palmer had gone to Jodrell Bank in the year I did, by the way. He had been doing work at Cambridge on weather, cloud physics.

Sullivan

Right. So when did you leave Jodrell, what year?

Thompson

It must have been, excuse me a moment, I got my Ph.D. in the year after, let me just get this right. I think it was 1955 that I left Jodrell. I left at the end of the year, and I went to work for EMI. Letís see, the name of the company was EMI Electronics Development Co. and the EMI stood for Electrical and Musical Industries. I worked on a guided weapons project there for about a year and a half. Letís see. Then I got my Ph.D. the following summer. I had written my thesis before I left, but Minkowski was going to be coming over again and Lovell and Hanbury decided that he could be my external examiner. So that went off perfectly well. He was a delightful guy, very nice guy to have as external examiner.

Sullivan

Can you tell me about this exam?

Thompson

I canít remember too many things about it. We talked a little bit about the distribution of radio sources in the sky and things like that. He was quite, he thought it was quite useful piece of work to have separated these two classes of radio sources by diameters.

Sullivan

How did you see these classes as relating to Millsí classes 1 and 2? He had this scheme between the large, tended to be large size associated with galactic plane and -

Thompson

I think they were very much the same. Mills had some galactic and extra-galactic and we were essentially dealing with the same things.

Sullivan

You said that, in a sense, you were competitors, but you didnít disagree very much.

Thompson

Oh, no we didnít. Using the word competitive, there was a kind of technological competition of how far can you get two antennas and still make an interferometer Ė that would have been the extent to which we were competitors.

Sullivan

But in terms of the scientific interpretation of it, you were coming to basically the same conclusion.

Thompson

Oh, yes. I think so. We never had any disagreement. And we were looking essentially at different sources. I donít think there was anything common to our two lists, oh, wait a minute, didnít Mills see Cygnus? I guess he did.

Sullivan

He could just see it, yes.

Thompson

So there were some Ė some were the same and some were different.

Sullivan

But unlike the 2C versus the Mills survey, there was no -

Thompson

There was no problem like that.

Sullivan

There was not any disagreement.

Thompson

No, no disagreement.

Sullivan

Now, one thing you mentioned earlier was about cable versus radio links. Did you use cable up to some point?

Thompson

Yes, thatís right.

Sullivan

How far out could you go with cable? And why did you switch over?

Thompson

Iím trying Ė if I looked in my thesis, which I should have brought with me I realize now, I could have told you where we changed over, but the cable we were using was just a thin 50-amp television feeder type coax Now that was nice to start with for short distances because we didnít have to worry about making transmitters and receivers for the radio link, and there was no problem about interference. But, of course, as you go very far, the attenuation increases exponentially in a cable at so many dbs per foot.

Sullivan

Right.

Thompson

And so you get to a stage where, well, itís a mixture of the problem of stringing cables across roads and things, and the attenuation. I donít think we went beyond the first one or two stations Ė there were some stations very close to Jodrell, one in a field up behind where we used the cable. Iím just trying to remember Ė we eventually had to go to radio links, but I donít remember.

Sullivan

Maybe a mile or something like that?

Thompson

Yes, roughly, that, yes.

Sullivan

And okay, another subject we havenít brought up is the rotating load interferometer, the concept, where did the concept come from and was it pretty straight forward to implement and so forth?

Thompson

Well, okay. We realized, of course, that the load would get so fast that the sources would get lost in the noise because they just would be very quick wiggles. The problem was that, of course, we werenít using a computer or anything to record the output. We just had a pen recorder and one wanted to keep a fairly long time constant to reduce the noise in the output. And -

Sullivan

So even a high speed strip chart wouldnít solve the problem.

Thompson

Thatís right. No, no, you wanted the long time constant. So you wanted to slow down the fringes. I have forgotten whether there were Ė there was Hanbury, myself, and (?). I donít know which of us, in particular, thought of it. It turned out to be not a very difficult thing to implement in our case, because the way the interferometer was made we had a small frequency offset between the local oscillator and the two amps, I think it was about a kilohertz. And then when you bolt together the two IFs and multiplied them together, coherent radiation produced a kilohertz beam frequency.

Sullivan

Right.

Thompson

And then we put that into a phase sensitive detector together with the reference from the two local oscillators. This was, we originally thought of doing this as being some, as having the advantages of phase switching in that it got rid of the DC component in the output. But being somewhat simpler to do, you didnít need to build any phase switches ahead of the front end. So it turned out, of course, that all you had to do was to change the phase of the ten kilohertz reference to rotate the fringes, so we had an old (?) resolver, a bit of old Army surplus equipment, which was used for measuring rough angles of gun mounts and things like that. We were able to use that as being a transformer with a rotating secondary to put a phase change in it. Do you have that picture there? I can actually show you. It was driven by a thing called a (belodine?) which was a servo motor which you could run at various speeds. And Henry Palmer used to set it up to the right speed, I think, by twiddling a potentiometer and looking at his watch as (?) Is this the right one? Here they are, sorry. This device here is it. This thing here is the (belodine?) which is driving through a mechano gear box here and this was the (?) resolver. On this gear, here, if youíre interested. (looking at photograph)

Sullivan

Look at these old tubes.

Thompson

Thatís a power supply. A power supply, power supply at the bottom. The signals from the 280 foot dish came in here, there was a pre-amp here. The pre-amps we used were a cascade circuit of the triode followed by a pentode. Normally one used either a grounded, 6AK5 pentode which was strapped to the triode which made a very good input stage, and that was followed by a grounded (?) triode. The two together made a thing called a cascode. Anyhow, this end right here was for the signals from the 218 foot dish. Signals from the radio link came in at this opposite end here and these two IF strips here which are on the left hand side of the photograph were to do with receiving the arrow and IF signals that came in over the radio link. These back up here, there two things were multiplied together in a, behind the panel up here, and the recorder here, had a, you see, this is an old loudspeaker.

Sullivan

(?)

Thompson

Screwed to the back of the chart recorder, and the chart recorders had a certain amount of (?) in them. That was driven at 60 hertz and rattled on the back to keep the pen from sticking. Other people in the building used to complain that it was (?) made a noisy rattling noise. But it was very effective.

Sullivan

I see. Okay. So, let me also ask you about division of duties. Between this group of Hanbury Brown, Palmer and Thompson, was sort of everyone handled everything or was it - ?

Thompson

Well, I was kind of the electronic, the main radio engineer there. Hanbury, really, just was the advisor to Henry Palmer and I. I built most of the equipment, Henry helped to get it going and really did a lot of work in running it. Hanbury essentially just advised us.

Sullivan

And what about the interpretation side of it? Was that sort of equal as to what you were getting?

Thompson

Yes. I think it was, more or less, equal. Hanbury, as I say, knew Minkowski, and, had a bit, had the advantage of knowing some of the radio astronomers. I remember, though, that in those days, I had a file of every paper on radio astronomy that had been published. At one stage, Iíd read them all.

Sullivan

That was possible then.

Thompson

It was possible. It was possible up to about 1955.

Sullivan

Right. Let me ask about how you saw the problem, if you can try to put yourself back in those days, what did you see radio astronomy as a field, I mean, what were its main problems to be resolved? Was it simply to find out the nature of the radio sources orÖwhat were the critical problems as you saw them?

Thompson

I think so. Naturally, I thought the experiment that I was working on was pretty important Ė to try to find the nature of the small unresolved sources, the ones that appeared to be isotropic. Were they like Cygnus or were they something entirely different? Incidentally, I remember that during about the last year that I was at Jodrell, Martin Ryle announced the results of the 2C survey.

Sullivan

Thatís right, 1955.

Thompson

And we, several of us from Jodrell, went down to London and listened to that presentation.

Sullivan

RAS meeting.

Thompson

Yes, thatís right, and it was at the Royal Astronomical Societyís headquarters on Piccadilly, and I remember being very impressed with it all. I was quite young then, and I hadnít much experience with science and I remember thinking that they had catalogued all these radio sources, theyíd looked at astronomical plates and were they were and most of them were, I think, there were practically no identifications. I remember thinking, ďWell, I guess this winds up radio astronomy.Ē

Sullivan

Sort of tied it all up, huh?

Thompson

How wrong could you be? Yeah, I remember thinking that. Several of us went down. Lovell went down, and Hanbury and Palmer and myself.

Sullivan

I wouldnít expect that someone like Hanbury would have thought this though.

Thompson

Oh, Iím sure he didnít. And Iím sure none of them did, except that was what I thought.

Sullivan

You were getting out of the field at that time, I guess you knew that.

Thompson

I was. Iím just trying to remember exactly -

Sullivan

I think it was the Fall of 1955 when he gave that talk.

Thompson

Yes. I also have a memory of that meeting that there were two very vociferous, and I may say, struck me as being somewhat shabbily dressed, gentlemen got up on the front row and had a very great deal to say. I wondered just what they were doing in this meeting, and I learned afterwards that they were Bondi and, I think it was, Gold.

Sullivan

Gold, yes? You just didnít know them.

Thompson

I didnít know them. That was another interesting thing I remember.

Sullivan

Iím still struck by the fact that the intensity interferometer had revealed that Cygnus was, perhaps, a double. Anyway, it modeled as a double anyway, and it was asymmetric in its distribution. And apparently you werenít worrying about that too much in your longer and longer baselines.

Thompson

I think the feeling was that you had to resolve them. As long as you couldnít resolve the source, there didnít seem to be too much point in worrying what direction you were observing. Itís quite true, maybe you couldnít resolve it east-west, maybe you would have done north-south, but we had a limited number of places we could go to.

Sullivan

Right, and you had several sources also.

Thompson

Oh, yes. We had about a dozen. So they wouldnít have all resolved at the same angle, so it was kind of a Monte Carlo situation.

Sullivan

How were these dozen chosen?

Thompson

Oh, they were from Hanbury Brownís paper and they were the stronger ones in it.

Sullivan

They were the ones that had survived, obviously, in terms of (?) frequency.

Thompson

Thatís right. And, as I say, we found practically no sources, I think, except Cygnus and Cassiopeia, which resolved out nicely at intermediate baselines; we either couldnít get the antennas close enough together or far enough apart.

Sullivan

And so then, once again, as much as you can remember how you felt at that time, in 1955 when you had this collection of a dozen sources which were only a few arc seconds or less in size, did this seem to prove to you that it must be outside the Galaxy? Or were you sort of open as to their nature?

Thompson

Well, they had been, Ryle had shown that these type sources were, more or less, isotropically distributed, so it was generally thought that they were either very close to the Sun or they were wide outside the Galaxy. I think it seemed very unlikely that they were very close to the Sun, since they were no optical counterparts of them and -

Sullivan

However, this made for tremendous luminosity, of course.

Thompson

Thatís right, yes. But then, as I say, one looked at Cygnus and said these things were a few percent of Cygnus in flux density. If you had Cygnus objects ten times as far away, you would be down to a few arc seconds.

Sullivan

And you wouldnít see them on the sky survey, either, or on the Palomar photographs.

Thompson

Thatís right. And they would be of comparable intensity to these things that we were looking at. That was about as far as we theorized.

Sullivan

So you were not thinking of radio stars, really, in your mind as you worked on these things.

Thompson

No, no. Because, as I say, that summer of í72, Baade and Minkowski had identified Cygnus and Cassiopeia and the Crab and there was nothing that went with stars.

Sullivan

Let me ask you about this 1957 paper in Observatory. Itís been said that this was a key paper in the sense that it, as you know, a few of these turned out to be quasars later on, and certainly that was not known at that time, but it was known that these were the smallest sources that had been measured. Do you see this as having been important in directing that field at that point, or is it only in retrospect that one goes back and say that they had isolated these sources?

Thompson

Well, the experiment didnít stop when I left Jodrell. Morris had joined the group and, no, wait a minute, I said earlier, didnít I, that Rosen had joined the group?

Sullivan

Yes.

Thompson

In fact, he didnít right away. Rosen came in a did another experiment using an interferometer at ten centimeters wavelength and it wasnít until he finished that he got his Ph.D. that he joined Palmer. And that was after I left, but Morris joined about the time that I left. But that experiment went on after -

Sullivan

So this was just a way-station really, are you saying, then, that longer and longer baselines?

Thompson

Yes, well, I was essentially responsible for building and setting up the first equipment in that interferometer experiment which continued, and I think you could say is continuing in (?)

Sullivan

(?)

Thompson

In a rather evolved form, now at Jodrell Bank.

Sullivan

I guess what I want to get at is, is this few arc second limit, is that more important than the other limits, was it only that you happened to write a little paper at that stage, in terms of what it was able to establish scientifically?

Thompson

I think we thought of the limits of the angular diameter being one of the important physical properties that you could actually go out and measure.

Sullivan

The particular value of few arc seconds, did you look up that as being significant? For instance, you were saying before in comparison with Cyngus A, (?)

Thompson

Yes, I think we did. Thinking in those terms, yes.

Sullivan

Okay.

Thompson

And if they turned out to be smaller, then they would indeed be objects with somewhat more remarkable properties, properties of Cygnus (?)

Sullivan

But you might not have been surprised if they had all begun to resolve at that point? And then you would think they were just all Cygnus Aís.

Thompson

Thatís right. Thatís one thing we might have thought.

Sullivan

Okay. Well, is there any other aspect of what you worked on at Jodrell in terms your publications here -

Thompson

Oh, I remember one other thing that happened. Whilst we were there, we had a visitor from the Soviet Union who was interested in polarization, and that was, let me see, that (?) doing some polarization measurements, and we must have been one of the first people to look for polarization in radio sources. We used our same interferometer, well, we used, let me get this straight. We used our same electronics, but we used two different antennas. There was on the top of the generator house at Jodrell, we generated our own electric power with diesels then. An antenna which had the property that you could rotate it around its own axis, it was about a 20 foot paraboloid.

Sullivan

Itís still up there if I remember from a couple of years ago.

Thompson

Youíre probably right, its rather like a flower on a stalk, and you can rotate it about the stalk. And then there was another paraboloid which had been made by the machine shop staff at Jodrell which was eventually to become one of Rosenís two dishes for his 10 cm. work, but you could rotate that as well. We put two feeds in each of these, two cross dipoles at 158 and connected them to our interferometer system. And we looked at Cygnus, Cas and Taurus.

Sullivan

Who was this Russian, do you remember?

Thompson

Iím looking in my -

Sullivan

This was in connection with synchrotron theory, I suppose.

Thompson

Yes, well, Iím looking at the paper in which we wrote it up and thereís Dombrovsky -

End Tape 103B

Click start to listen to the audio for tape 104A of the 1978 interview.

Begin Tape 104A

Sullivan

Continuing with Dick Thompson on 1 May 1978.

Thompson

I donít remember, positively, the name of the Russian scientist who visited with us and talked with Hanbury Brown about that. But it did start us off, making a measurement of polarization, to which we only got upper limits of a few percent. But that was an interesting (?)

Sullivan

I think youíre right, I donít remember any earlier experiments along those lines.

Thompson

I think Cambridge had done it.

Sullivan

On radio sources, also?

Thompson

Iím pretty sure, yes, we were not the first to look for polarization of radio sources, but we were perhaps the second. Or was it Ryle and Smith, I think, did it?

Sullivan

I just donít remember.

Thompson

It says, ďThe only published experiments appear to be those of Ryle and Smith who examined the intense source of Cygnus and Cassiopeia with interference polarimetry.Ē

Sullivan

Okay. So they only looked at the two biggest.

Thompson

Yes.

Sullivan

What was the feeling as to the emission mechanism of the radio sources at that time? Sort of a big unknown?

Thompson

I think certainly after that 1954, sorry 1955, meeting, it was understood that it was synchrotron mechanism.

Sullivan

But before then.

Thompson

It was something of an unknown, yes. Going back to the polarization (?) It had just been discovered optically in the Crab. That was what was being talked of, and that was the reason why we looked for it in the Crab.

Sullivan

Oh, was that one of the sources you looked at?

Thompson

Yes, we (?) Cygnus and Cassiopeia.

Sullivan

Oh, was that -

Thompson

Cygnus, Cassiopeia, and the Crab were the three we looked at.

Sullivan

And Cas was known to be a supernova remnant. Well no, thatís not true, its nature wasnít clear, it was a nebulosity with a high velocity, but whether it was a supernova remnant, I think was under debate at that time.

Thompson

Yes, I think youíre right.

Sullivan

Okay. Well, that gives me a good coverage of the projects that you worked on at Jodrell. I might ask one general question about the whole way Jodrell operated. It obviously was one of the leading radio astronomical centers in the early fifties and to what do you attribute that? What, do you think, was the key ingredient?

Thompson

Well, the British got off to an early start in radio astronomy and as of course, so did the Australians. I think it was due, very largely, to Lovellís enthusiasm, of course. He was a great pusher at getting things going. It started, of course, not in radio astronomy as we know it now, but in meteor radar, and the 218 foot dish was built for cosmic ray experiments to detect cosmic ray showers by radar.

Sullivan

That was the initial thing, which Lovell had proposed during the War. The idea was something that he had proposed during the War.

Thompson

I see.

Sullivan

But I had forgotten that that was the original purpose, and was that experiment carried out?

Thompson

Yes, I believe it was, with negative results. But that was before I went to Jodrell, and the dish had been, someone had attempted to do a survey with that dish using an open wire feeder up the mast at about 100 megahertz, and it wasnít very satisfactory. And Hanbury came along and used a much better feed, put it in a (?) feeder, and much better receiver, and was able to do a satisfactory sky survey. I guess it was just, it was partly because they got going so soon, I think. Partly because of meteor because, well, the meteor radar stuff turned out to be a very fruitful field, only it lasted about 10-15 years, but during that time it was very fruitful. A great deal was learned about the high atmosphere from it; the observations were relatively straightforward. They were rather easy with the radars that had been developed during the second World War. Cambridge came into it and was never in the meteor field, but they came straight in to the radio astronomy aspect. They Ė Ryle was probably more interested in cosmology and that kind of thing right from the beginning.

Sullivan

Right from the beginning, you think so?

Thompson

Well, from early on, I would, maybe I shouldnít say right from the beginning, but I suspect that within a year or two of finding that he could catalogue radio sources, I suspect that was when he got interested in it.

Sullivan

So that would be around 1950 or Ď51, probably. The 1C was published in 1950, so he was working on it in 1949.

Thompson

Of course, he did a little bit of solar work, too.

Sullivan

Oh yes, quite a bit in the late forties.

Thompson

Yes, okay.

Sullivan

He started working on the sun for two or three years.

Thompson

Thatís right.

Sullivan

So the enthusiasm of Lovell, the fact of getting in early, any other aspects that you would - ?

Thompson

Well, there were a lot of good people, I think, associated with things in those early days. Hanbury Brown, there was a man called Clegg who wrote a small book on radio astronomy with Lovell.

Sullivan

Yes, Iím familiar with that.

Thompson

He taught electromagnetism at Manchester University; I took one of his courses. He was an ex-RAF type, who had worked a great deal on radar during the War. He was very good at putting up antennas and making them work. I think he didnít get along too well with Lovell, somehow or other, they didnít quite have the same style. And he eventually left. But he did enormous amount of work in the early days getting the meteor radars going.

Sullivan

You bring up the question of the courses and so forth, how much optical astronomy did a research student at Manchester learn in those days?

Thompson

Well, none. I was taking physics. And there was very little in the way of post-graduate coursework.

Sullivan

So this was an undergraduate course you were talking about?

Thompson

Yes, oh yes.

Sullivan

So as a research student, you took very few courses at all.

Thompson

Thatís right, mainly a few seminars and things.

Sullivan

So what you learned was from your own readings and the literature.

Thompson

Thatís right, yes.

Sullivan

Did you, more or less, in the reading of the literature, pay attention to the more traditional astronomical papers or was it pretty much just reading of radio papers?

Thompson

I think a mix of the two. I might just mention the business of people coming to the United States from England, Gordon Little, who is now, I think, at Boulder, was the first one, I think, to come, and then Alan Maxwell and various other people, I know I was third or fourth.

Sullivan

J.V. Evans.

Thompson

Yes, J.V. Evans came after me. I knew him fairly well at Jodrell. I think he came to Jodrell either one year or two years after I did, one year I think, and we were very good friends there. And, of course, Dave Williams had gone to Canada. Dave Williams is now at Berkeley and he worked with Marconi in Canada for a number of years.

Sullivan

What about this out flux?

Thompson

I guess we heard from people whoíd gone that, what an interesting and exciting place the United States was, and it seemed like quite an adventure to come over here, so when I eventually got the opportunity, I did so. I came over and have never regretted it. Actually, what happened was that when I left Jodrell, I thought it would be fun to work in industry for a while, and probably have rather better instrumentation and stuff to play with than we had at Jodrell. So I joined EMI. Iíd been there for just over a year, and one afternoon I had a phone call from Alan Maxwell who was in London, and he was interested in the possibility of my going over and joining him at Ft. Davis. So I went and had lunch with him, and he asked me to think about it. I decided that it would be an interesting thing to do, to come to the United States. So I came in 1957 and I stayed at Ft. Davis for five years.

Sullivan

Is it fair to say that there really werenít that many opportunities to do radio astronomy in Britain as far as saturated in terms of positions Ė it was expanding (?)

Thompson

No, I could have stayed on at Jodrell if Iíd wanted to.

Sullivan

Was the staff expanding then, to that extent, that there were some positions for the best students anyway?

Thompson

Yes.

Sullivan

Okay.

Thompson

Yes, it was. You see, the 250 foot dish was not quite completed when I left, but quite a lot of work was going on building instrumentation for it, and I could certainly have stayed and worked.

Sullivan

Well, that would seem to be a very exciting prospect to have that thing coming on the air.

Thompson

Yes, thatís right. But I guess I was young a felt that a change in horizons would be in order.

Sullivan

Okay. So you came, did you live at Ft. Davis immediately?

Thompson

Yes.

Sullivan

And what did you find there and what did you being working on?

Thompson

Well, the Ft. Davis project had been going for about a year when I arrived there. Sam Goldstein and Govind Swarup were both working there. I remember that the first day I went out to the site, Alan Maxwell introduced me to them and I looked at the equipment and they had this very complex antenna which would cover about three octaves of the radio spectrum. And all these sweep-frequency receivers and I eventually looked at the, got familiar with the equipment, and the sweep-frequency receivers were, of course, mechanically tuned and were getting a little bit out of tolerance and bearings and things were wearing, so I took one to pieces and changed some of the mechanical things and put it together and arrived at mechanically somewhat better than it had started with. That became one of my annual jobs for the five years I was there.

Sullivan

A tune up, so to speak.

Thompson

Yes, taking the sweep-frequency receivers to pieces and tuning them up.

Sullivan

I see. Was there any possibility in terms of the technology to make it electronically tuned or was that out of the question in those days?

Thompson

I think it was kind of on the horizon, we, well, before I left Ft. Davis, we had gotten a receiver that covered two-four gigahertz, sweep-tuned using a backward wave oscillator, which wasnít very reliable, incidentally. But the thought of doing that at the lower frequency was an impossibility. Incidentally, I believe those receivers are still running. On the 28 foot dish. We eventually got two more of them which were 25-50 and 50-100 megahertz, so we scanned all the way from 25-600 and those two were connected to a pair of dipoles. At about this time, Paul Wild had done a lot of work classifying solar bursts and we, I think, one thing, well, some of the main contributions of that particular work at Ft. Davis were getting a regular and reliable solar watch going so that we had good catalogues of radio bursts and we could easily classify them into the four types, noise storms, slow-drift bursts, fast-drift bursts, continuum and finally, the type 5s.

Sullivan

Are you implying that DAPTO at that time was not monitoring regularly, or was it just a matter of the other half of the day?

Thompson

Well, it was partly due to the other half of the day. I think they were monitoring fairly regularly. I donít think they had quite as good a time coverage as we did, we managed to get to about 95%-time coverage.

Sullivan

Iím not quite sure how much they had, they certainly were going well in those days.

Thompson

Thatís right, but then, well, another important thing was, of course, that the United States had a number of very good optical solar observatories and one wanted really good coverage during those periods where we could correlate flares with solar radio bursts.

Sullivan

Which observatories were you working with mainly?

Thompson

Oh, Sac Peak and High Altitude Observatory. And then Gayle Morton, who was a guy who worked for Lockheed, started a solar observatory on the West Coast, which turned out to be quite good. He produced a lot of very good solar data.

Sullivan

This is when the military was putting out money for that sort of thing.

Thompson

Thatís right. He eventually went to Australia and I lost track of him. I donít know whatís happened to him. But we did a lot of work on the coincidences between different types of solar flares and different intensities with solar radio bursts.

Sullivan

Before we get into the scientific results of that, let me just ask about the equipment. Is it fair to say that it was a direct outgrowth of Paul Wildís dynamic spectrographs?

Thompson

The idea of using a dynamic spectrograph was. The actual receivers were an outgrowth of, I think, the military, who had, they were made by AIL, who had made similar things for the military, they were classified, but I think it was generally known that they were used in the Mediterranean area for monitoring missiles and all that kind of thing.

Sullivan

Or just radio communications.

Thompson

Thatís right. You could stop them and tune them into a particular frequency.

Sullivan

And what were the improvements Ė I think this had somewhat better specs than Wildís spectrograph.

Thompson

Yeah, we had, we went at a higher frequency to 500 megahertz. We had somewhat, I think, flatter frequency responses. Those were the main things. We had a somewhat better antenna. We had, he had, dipoles and things, we had a paraboloid to track, with a very nice feed made by Henry Jassick.

Sullivan

Another thing that strikes me is that you had not worked on the sun at all, of course, at Jodrell and yet you were quite willing to change the scientific thrust of what you were doing. Did that matter to you at all or was it just that you were happy to be doing radio astronomy?

Thompson

I was happy to be doing radio astronomy, I was always considerably interested in the techniques as well, and I still am, of course, as well as the astronomy.

Sullivan

Right. So now letís get on the scientific results that came out of this monitoring. What, would you say, are the primary Ė the papers here seem to talk about the correlations between cosmic rays and type 3 and 4 bursts quite a bit.

Thompson

Yes, we did some of that. Let me think, one of the things that we discovered was that there was a very strong correlation between type 4 bursts and (?) absorption phenomena. And we wrote that up in a little Nature article; I think the Japanese just beat us into getting that into print. They had discovered it, too.

Sullivan

I guess, was the reason that you were worrying about ionospheric effects, perhaps, more than you would have otherwise, because of Alan Maxwellís background?

Thompson

Yes, I think perhaps so.

Sullivan

And what about the sun itself? What, would you say, were the things that you learned about the sun from this monitoring?

Thompson

I never regarded myself as a solar physicist in any way, and I think we were doing this in a rather empirical fashion, but we were interested in the quantitative descriptions of the bursts.

Sullivan

And correlations.

Thompson

And the correlations. We were interested, of course, in the theories about how the bursts were produced. We werenít exactly, neither Maxwell nor I, would ever regard ourselves as plasma physicists or theoretical physicists, theoretical astrophysicists. Alan was always trying to get Max Crook at Harvard, who was a great friend of his, to write a paper on the mechanisms of solar radio bursts, because Crook had quite a number of ideas, but I donít think he ever did. Alan used to try desperately to get some kind of notes from Crook to put in some of the papers that we wrote.

Sullivan

This was a fellow in the Department of Physics at Harvard?

Thompson

I think; I donít know if he was applied physics or mathematics.

Sullivan

I just noticed here that it says in the Proceedings of the IRE paper in 1958 that you had ten times more sensitivity than anyone else, which means that Wildís -

Thompson

Yes, of course -

Sullivan

(?)

Thompson

Fred Haddock started up about the same time on Navy sponsorship, and there was a certain amount of competitive feeling between him and Alan.

Sullivan

What was the main source of the money for Ft. Davis?

Thompson

The Air Force, through Sacramento Peak.

Sullivan

Oh, I see, it came via that.

Thompson

Ed Dennison of Sac Peak -

Sullivan

Thatís right, Menzel -

Thompson

Ed Dennison of Sac Peak was our contract monitor; Menzel, yes, had helped to set up Sac Peak in the early days.

Sullivan

Right, I was able to talk to him before he died.

Thompson

Letís see, there was something that just crossed my mind. (pause) Oh well, never mind.

Sullivan

What, would you say, were the primary differences in the way radio astronomy was developing in the late Ď50s in U.S. as opposed to Great Britain?

Thompson

There was great deal more emphasis in centimeter waves. We all started in England on meter wavelengths, and the U.S. never really went through that. They passed it because their centimeter wavelength technology was a higher level and they kind of jumped in there.

Sullivan

Well, also, I guess, because they got started late and that was the direction that things were going -

Thompson

Yes, partly that. Thatís right.

Sullivan

Direction things were going. But even the NRL group, in the late Ď40s, was working at centimeter waves. They never worked anything lower than 20 centimeters.

Thompson

Thatís right 21 cm. was about the longest wavelength.

Sullivan

I guess that is generally true for the entire, all the U.S. groups, with only a couple of exceptions. Okay. Just to finish up, you were there until 1962?

Thompson

Yes.

Sullivan

And then you went to -

Thompson

Stanford, yes. Ron Bracewell, yes, who, at that time, was hoping to make himself a large cylindrical antenna, but the money for it never came through.

Sullivan

A Cambridge type paraboloid, you mean?

Thompson

Well, it was going to be a cylinder that worked at 10 cm wavelengths with some kind of long feed.

Sullivan

For primarily solar work?

Thompson

No, for the whole thing. He was very keen on the idea of a growing array.

Sullivan

A what kind?

Thompson

A growing array. Or an instrument which you could add to, and at that time, it wasnít so clear that he wanted resolution, but you wanted collecting area. And the thought was that you had one of these long trough-like cylinders, you could add to it and make a very large square array. It would have been a meridian transit instrument, largely.

Sullivan

I see.

Thompson

And so Iím not, as things developed, that wasnít the way to go.

Sullivan

And the money didnít come through.

Thompson

The money didnít come forth for him.

Sullivan

So the effort at Stanford shifted in what direction then?

Thompson

Well, it shifted into making some paraboloids for a five element array.

Sullivan

Even that early?

Thompson

Well, let me see, maybe Iím, I shouldnít say that early. Stan Zisk was there at this time; we had some 30 foot dishes, I think it was three of them, and those were put on mounts and we worked at ten centimeters, we did some ten centimeter interferometry and that led into the 2.8 cm array that Ron eventually built.

Sullivan

And just to finish off your career, when did you become director of the VLA site?

Thompson

Well, letís see, I joined NRAO in 1972, so I had worked, it would be just five years at the beginning of this year. In January of 1972. My title is Deputy Project Manager under Jack Lancaster. The exact date, Iíd have to dig out of my files.

Sullivan

Well, letís not take that time.

Thompson

I would say 1974.

Sullivan

Well, thank you very much. This ends the interview with Dick Thompson at the VLA in New Mexico on 1 May 1978.

End Tape 104A


Modified on Tuesday, 11-Oct-2016 13:59:51 EDT by Ellen Bouton, Archivist (Questions or feedback)