Interview with A. Richard Thompson

Sullivan: 00:01

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

Thompson: 00:15

All right. I went to a grammar school in England. It was academic 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. And I mainly worked there helping one of the guys who was doing experiments on meteor radar. It was the radiant experiment.

Sullivan: 01:05

What was his name?

Thompson: 01:06

Gee, let me think. I have difficulty recalling.

Sullivan: 01:15

That's okay.

Thompson: 01:15

He's not in radio astronomy now. He left and I think he went into an electronic industry or something like that. I remember spending a couple of days during the summer helping Hanbury Brown and Hazard move the tilting mast of the 280-foot to--

Sullivan: 01:31

To a different declination?

Thompson: 01:32

Yeah, to a different declination. That's right. Yeah. But mainly, I was working with the media people. Then, the following summer, I wasn't at Jodrell the summer after that, which was the summer I graduated with a bachelor's degree. I was there again. And let's see. What was I doing that summer-- that second summer as a graduate student? Was that when I was working with Dennis [Walsh], or Hanbury Brown, or who? Well, never mind. That's not important. And then, I decided I'd like to do a Ph.D. and do work in the summer. So I went to Jodrell And three of us went from the physics department that year. There was Matthew [Dag?], myself, and Colin Gill. And Matthew Dag worked with Alan Maxwell. They had an experiment where they were following Cygnus or Cassiopeia to measure ionospheric scintillation. After he got his Ph.D., he went to Cambridge and took a course in soil physics. And I think he's now director of a research station in Africa. Gil did an experiment with -let's see- not R.D. Davies, the other Davies—John Davies.

Sullivan: 02:57

J.D. Davies.

Thompson: 02:57

J.D. Davies. Yes. And 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: 03:14

From a different doppler shift at a different -

Thompson: 03:16

That's right. But they could get both-- they could get the precise orbit, which you can't do by just looking at it with a-- with transmitting and receiving from the same place. And this was to see if there were any medias with hyperbolic orbits and they did that experiment. Gil got his Ph.D. and left. And as I said, I think he went into one of the British government agencies. I'm 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 the dish was implemented for 158 megahertz which was a fairly high frequency in those days. And we made an interferometer.

Sullivan: 04:13

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

Thompson: 04:19

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 if the three of us going, Gil and Dag and I, we settled it between ourselves. I think my preference was to join Hanbury although I did wonder about doing the meteors. And Gil, I think, said, well, he just did just assume to the meteors and Dag did the other one, and that's the way it worked out. Kind of by mutual agreement.

Sullivan: 04:55

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

Thompson: 05:03

Well, he had given the idea of the radio version of the intensity interferometer to Jennison and Jennison and Das Gupta had made it and about that summer. Let's see. That would be 52'. The summer 52'. Jennison and Das Gupta were about to make their first measurements. And with the intensity interferometer. The inner front that we were going to build was going to be a regular interferometer with a cable or radio link. We made a fairly transportable antenna. I actually made most of it myself made out of two-by-fours bolted together with bolts and it had four frame sections each of which had, I think ….  But it had four full wave dipoles on each frame section and the frames stood side by side and then a single screen of chicken wire as a ground plant went underneath the layer of dipoles.

Sullivan: 06:11

And this all folded up nicely to be put in the background.

Thompson: 06:13

Yeah, pretty much. Yes. It came into the four frames took down and I think it was possible. I forgot whether we removed 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 meant a little bit easier to make. And then we separated the signals at the home station, which was a heart of Jodrell Bank which is called the Park Royal. I don't know whether you ever knew about it.

Sullivan: 06:55

Park Royal.

Thompson: 06:56

Did you know about that?

Sullivan: 06:57

No, I haven't heard that term.

Thompson: 06:58

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

Sullivan: 07:27

The Moon Hut was for lunar radar.

Thompson: 07:30

Lunar radar, there was meteor radiant hut that was-- let's see, there was the-- I forgot the name of the other as well. It doesn't really matter.

Thompson: 07:45

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 a 10 megahertz crystal which would multiply it up to a 150 to beat 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, yeah, the 280-foot diameter antenna, and the output went on a chart recorder. When we got to long spacings with that system, we--

Sullivan: 08:29

You successfully moved out, I guess, going further and further. Was that the idea?

Thompson: 08:32

Yes, well, that's right. Well, let me go back. At the time, Hanbury Brown had produced a catalog of radio sources at 158 megahertz. And comparing this with the catalog which Ryle had produced, a certain number of sources which Hanbury Brown found near the galactic plane. And these of course were found with the same antenna, a 280-footer, but in a single dish mode. The ones near the galactic plane were not in Ryle’s 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 s to the beam width of the antenna. And we found that it was very difficult for us to get our antennas close enough together to pick up these big ones. They were almost fully-- well, they were resolved to maybe 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 couldn't go far enough to resolve them. We ended up by taking the antenna out to the Cat & Fiddle Hill, which is kind of hill or mountain, in Derbyshire, which was 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, but--

Sullivan: 10:03

How long was that baseline roughly?

Thompson: 10:05

Well, let me see. If you consult-- there's an Observatory paper of which you probably have the--

Sullivan: 10:15

The one in 57 with the--?

Thompson: 10:17

Morris, Palmer, and Thompson.

Sullivan: 10:19

Right. Right.

Thompson: 10:20

Okay. And was 10,600 wavelengths at--

Sullivan: 10:28

Two meters roughly?

Thompson: 10:29

Yeah, at 158 megahertz. So you could figure that out. I think actually, we didn't--

Sullivan: 10:34

About 20 kilometers though?

Thompson: 10:35

Yeah. I don't think we said exactly what it was in miles or kilometers.

Sullivan: 10:46

That's all right. It's roughly 20 kilometers, but what I wanted, did you make a big jump out to this 20 kilometers from your previous baseline or was it …?

Thompson: 10:53

No, we went out to three or four places, three or four intermediates. Well, let me give you again what they are in wavelengths.

Sullivan: 11:03

And so it was a successive effort to try to resolve these things.

Thompson: 11:06

That's right. We'd gone to 56 wavelengths, I guess, for 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 into their electric power supply.

Sullivan: 11:37

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

Thompson: 11:41

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

Sullivan: 12:06

And were these baselines all roughly east-west?

Thompson: 12:09

No.

Sullivan: 12:10

No?

Thompson: 12:10

Here again, just a moment, I--

Sullivan: 12:19

Well, in any case, if you're observing a meridian, you're only getting the east-west structure.

Thompson: 12:23

No, you're getting the structure with regard to whatever the baseline is.

Sullivan: 12:28

No, but only in the east-west direction though.

Thompson: 12:30

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

Sullivan: 12:43

That's what I'm trying to get at. Were you worried about that effect, or were you just-- the possibility of asymmetric sources?

Thompson: 12:48

At that time-- well, that was kind of a secondary consideration, and I would-- no, essentially we weren't. 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 radio version of the intensity interferometer. And we're just trying to push things in the same direction as 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: 13:26

I think you're right. I think it was around 78 or something, right?

Thompson: 13:27

Yeah. 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, Jodrell Bank to 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 "Five-hour Source" because it had a right ascension of almost-- yeah, it had a right ascension of near five hours. It was about four hours and fifty something minutes. And Minkowski visited Jodrell and we talked to him about it.

Sullivan: 14:24

Now what time would this-- what year would this be roughly? Was this at the Jodrell Bank meeting perhaps in '55, the--

Thompson: 14:30

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

Sullivan: 14:57

"Large Angular Radio Sources near the Galactic Plane."

Thompson: 15:01

"Galactic Sources of Large Angular Diameter" is the name of it.

Sullivan: 15:04

In Nature.

Thompson: 15:05

Yes, in Nature.

Sullivan: 15:06

In '54. But now that would be before, if Minkowski had visited you, then, that was--

Thompson: 15:10

Now maybe I've 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: 15:29

Oh, Cygnus and Cas, yeah.

Thompson: 15:30

And it could have been that it was a result of correspondence-- the subsequent correspondence that Minkowski sent us. This photograph, but.

Sullivan: 15:42

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

Thompson: 15:44

Yes, that's right. Yes.

Sullivan: 15:45

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

Thompson: 15:48

Well, to tell you the truth--

Sullivan: 15:52

It's a supernova remnant, I guess.

Thompson: 15:53

Yes. And it centered on the star Alpha Auriga

Sullivan: 16:01

Oh

Thompson: 16:01

No. Wait a minute. No, it's not. It's centered on BD 46 degrees. Now 9 49.

Sullivan: 16:06

But it's in the constellation of Auriga.

Thompson: 16:08

Yeah. It's near Auriga. It's about declination between 46 and 47 degrees, and right ascension about 4 hours and 58 minutes.

Sullivan: 16:17

Okay. I'll have to check that out. Yeah. I remember this. So this was a supernova interview that was studied often in the 50s.

Thompson: 16:25

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

Sullivan: 16:46

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

Thompson: 16:51

Well, for me, because it was the first time I've 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 when one had the opportunity to see some of them and meet some of them. Well, I remember Fred Haddock was there talking about some measurements he'd done at 10 centimeters, which was just an incredibly short wavelength in those days. Those were done with the old Naval Observatory dish. That was when he was at the Naval Observatory.

Sullivan: 17:29

NRL. Yes.

Thompson: 17:30

I beg your pardon. NRL. Yeah. Naval Research Lab, that's right. And 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. And I remember that after that there was a paper by, I suppose maybe it was Shklovskii or one of his colleagues, if it wasn't Shklovskii, it was another Russian who always used to come to meetings in those early days and wrote papers for his colleagues [ed. Vitkevitch].  I forgot what his name was. Anyhow, after it, I remember-

Sullivan: 18:26

Proposing synchrotron radiation.

Thompson: 18:27

Yeah. Proposing synchrotron. Right. That's right. I remember Minkowski getting up and saying, "I think we should withdraw our paper." Jesse, and Jesse said, yes. It's kind of interesting that these guys were so willing to--

Sullivan: 18:51

As soon as I heard about this.

Thompson: 18:52

Yeah.

Sullivan: 18:53

They were superior.

Thompson: 18:54

That was much superior. And I was kind of impressed by that.

Sullivan: 18:58

That's interesting. I never heard that story before. Who else? What about the Australians? You've never met any of them, I suppose.

Thompson: 19:05

No, that's right. Mills and Christensen were there and they were interested. Mills is interested in seeing our interferometer. Ryle was there. I guess that Paul Wild was there. I met him subsequently  

Sullivan: 19:21

Yes. He was. Because I just interviewed him.

Thompson: 19:23

I see.

Sullivan: 19:23

And also Joe Pawsey was there.

Thompson: 19:26

Ah, that's right. Yes. And Bolton was there. And Bolton at the time was talking about getting some dishes going in California. Which of course, he eventually did.

Sullivan: 19:39

You mentioned that Ryle was there, is the implication that you hadn't had much contact with Cambridge until it took an international meeting to get contact between the two groups?

Thompson: 19:49

No, there was some contact, but not a lot. I had met him before. Hanbury knew him. They were on good terms. But I think they'd always been a little bit of question as to whether pencil beams or interferometers were the things to use for sky surveys and it was interferometer and Hanbury was using the pencil of the 280-foot dish. I don't know. Ryle was very interested when we were just beginning to get these results. I think, at that time about-- no. maybe we already resolved out the big sources and we knew the answer about why Ryle could see them. And 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 start to resolve out fairly quickly. And we found, of course, that they didn’t.

Sullivan: 21:05

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

Thompson: 21:10

Yes. Oh, yeah, yeah. He may have thought they weren't very important. I don't know. But sure, yes. He accepted that. Of course, he was interested in the cosmological aspect, that's why I say it might be particularly important at that time. Let's see. Yeah. we had some very crude ideas in mind like the intensities of some of these sources suggested they might be objects like Cygnus, but 10 times as far away. And therefore, the angular diameter might be on the order of one-tenth that of Cygnus. And we were getting down to a few-- we're getting down to a few arc seconds. So we were beginning to hit that. But really, I left at about really we got much further with that experiment. And Rowson, Barry Rowson, came along and joined Palmer on that. Palmer gone to Jodrell Bank the year before I did, by the way.  He had been doing work at Cambridge on weather, cloud physics.

Sullivan: 22:24

So when did you leave the Jodrell? What year?

Thompson: 22:30

It must have been - excuse me, a moment. I got my Ph.D. the year after. Let me just get this right.

Sullivan: 22:41

Go ahead.

Thompson: 22:42

I got my PhD-- it was 1955 that I left Jodrell.   I left at the end of the year, and I went to work for EMI was the-- let's see, the name of the company was EMI Electronics Development Company. And the EMI stood for electrical and musical industries.  And we worked on a guided weapons project there for about a year and a half. Let's see, and 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 had decided that he could be my--

Sullivan: 23:34

External--

Thompson: 23:34

--external examiner, yes. So that went off perfectly well. He was a delightful guy. A very nice guy to have for an external examiner.

Sullivan: 23:42

Can you tell me about this exam? Did he--?

Thompson: 23:46

I can't remember too many things about it. We talked a little bit about the distribution of radio sources in the sky and things like that. And he thought it was quite useful piece of work that separated these two classes of radio sources by diameters.

Sullivan: 24:06

How did you see these classes as relating to Mills' classes one and two? Remember he had this scheme between the large size associated with galactic plane, and--

Thompson: 24:19

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

Sullivan: 24:30

So although you said that, in a sense, you were competitors, you didn't really disagree very much on the--

Thompson: 24:34

Oh, no, we didn't. No, I mean, using the word competitive, there was a kind of a technological competition in how far apart can you get two antennas and still make an interferometer. That would have been the extent to which we were competitive.

Sullivan: 24:51

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

Thompson: 24:55

Oh yeah, I think so. Yeah, we never had any disagreement. And we were looking essentially at different sources. I don't know whether there was anything common to our two lists. Oh, wait a moment. Did Mills see Cygnus? Yes, I guess he did.

Sullivan: 25:08

You could just see it, yeah.

Thompson: 25:09

Yeah, so there was some. Some were the same and some were different. So there was--

Sullivan: 25:17

Unlike the 2C versus the Mills survey--

Thompson: 25:19

Yeah, there was no problem.

Sullivan: 25:23

One thing you mentioned earlier was about cable versus radio links. And did you use cable out to some point?

Thompson: 25:29

Yeah, we did. That's right.

Sullivan: 25:31

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

Thompson: 25:36

Well, 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 ohm television feeder type coax. Now, that was nice to start with for short distances because you didn't have to worry about making transmitters and receivers for the radio link. And there's no problem about interference. But of course, as you go very far, the attenuation increases exponentially in a cable in so many dbs per foot. And so you get to a stage where, well, it's a mixture of the problem of stringing cables across roads and things and the attenuation. I don't think we went beyond the first one or two stations. There were some stations fairly close to Jodrell. And one in a field up behind where we used the cable. I'm just trying to remember. We eventually had to go to radio links. And I don't just remember exactly where.

Sullivan: 26:55

Maybe a mile or something like that?

Thompson: 26:56

Yeah, something roughly that. Yes. Yes.

Sullivan: 26:59

Okay. Now another whole subject we haven't brought up is the rotating lobe interferometer, the concept. Where did the concept come from? And was it pretty straightforward to implement, and so forth? I mean, it was a new thing.

Thompson: 27:15

Okay. We realized, of course, that the lobes would get so fast that the sources would get lost in the noise because they'd just be very quick wiggles. The problem was that-- because we weren't using a computer or anything to record the output.  We just had a pen recorder. And I wanted to keep a fairly longtime constant to reduce the noise in the output.

Sullivan: 27:42

So even a high-speed stripchart wouldn't solve the problem.

Thompson: 27:44

That's right. No. No. You wanted the longtime constant. So you wanted to slow down the fringes. And I have forgotten whether there was three, Hanbury, myself, and Palmer. And I don't know which others. I didn't particularly 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 oscillators at the two ends. I think it was about a kilohertz. And then when you brought together the two IFs and multiplied them together, the coherent radiation produced a kilohertz beat frequency. And then we put that into a phase-sensitive detector. Together with the reference from the beat of the two local oscillators. We originally thought of doing this 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 didn't need any to build any phase switches ahead of the front ends. So it turned out, of course, that all you had to do was to change the phase of the 10-kilohertz reference to rotate the fringes. So we had an old max slip resolver, which was a bit of old army surplus equipment, which was used for measuring rough angles of guns and gun mounts and things like that. And we were able to use that as being a kind of transformer with a rotating secondary to put a phase change in-- do you have that picture there that I can actually show you? It was driven by a thing called a velodyne 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 the potentiometer and looking at his watch, [laughter] as we went -- now, is that the right one? No, this is the right one. Here they are, sorry. I've got the wrong button. This device here is it-- this thing here is the velodyne, which is driving through a Mechano gearbox, right here. Yeah. And this was the-- the max slip resolver, which did the …. On this gear here, if you're interested, ….-

Sullivan: 30:38

Look at these old tubes, wow.

Thompson: 30:39

Now, that's a power supply. Those are power supplies. Power supply, power supplies at the bottom. The signals from the 208-foot dish came in here. There was a preamp here. The preamps we used were always a cascode circuit of a triode followed by a pentode. Normally, one used either it either as a grounded grid 6AK5 pentode which was strapped as a triode, which made a very good input stage, and that was followed by a grounded-grid triode. The two together made a thing called a cascode. Well, anyhow, this end right here was for the signals from the 208-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 LO and IF signals that came in over the radio link. And then back up here, the two things were multiplied together behind the panel up here. And the recorder here had a-- as you'll notice, there's an old loudspeaker.

Sullivan: 31:57

Oh, is it screwed -

Thompson: 31:58

It's screwed to the back of the chart recorder. And the chart recorders had a certain amount of stiction in them. And 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--

Sullivan: 32:14

This hum.

Thompson: 32:15

That it hummed and made a noisy rattling noise. But it was very, very effective.

Sullivan: 32:20

Very effective.

Thompson: 32:20

Yeah.

Sullivan: 32:21

I see.  Okay, so let me also ask you about the division of duties between this group of Hanbury Brown, Palmer, and Thompson, was sort of everyone in on everything or was it--?

Thompson: 32:33

Well, I was kind of the electronic-- the main radio engineer there. Hanbury really just was the adviser 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. And Hanbury, essentially, just advised us.

Sullivan: 33:00

And what about the scientific interpretation? Was that sort of an equal-- as to what you were getting, or? How did that go?

Thompson: 33:06

Yeah, I think it was more or less equal. Hanbury, as I say, knew Masłowski and 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. And at one stage, I'd read them all.

Sullivan: 33:30

[laughter] That was possible then, yeah.

Thompson: 33:32

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

Sullivan: 33:38

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, or-

Thompson: 34:00

Yeah. Yes, I think--

Sullivan: 34:01

--what were the critical problems as you saw them?

Thompson: 34:02

I think so. Naturally, I thought the experiment that I was working on was pretty important, trying 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: 34:42

That's right, '55.

Thompson: 34:43

--the infamous 2C survey. And several of us from Jodrell went down to London and listened to that presentation.

Sullivan: 34:55

The RAS made.

Thompson: 34:56

Yes, that's right. And it was at the Royal Astronomical Society's headquarters on Piccadilly, and I remember being very impressed with it all. I was quite young I guess, and I hadn't much experience of science. And I remember thinking that they'd cataloged all these radio sources, they'd looked at astronomical plates and where they were and most of them were-- I think there were practically no identifications. And I remember thinking, "Well, I guess this is-- this winds up radio astronomy." [laughter]

Sullivan: 35:38

Sort of ties it all up, huh?

Thompson: 35:41

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

Sullivan: 35:56

I wouldn't expect that someone like Hanbury would have thought this.

Thompson: 36:00

Oh, I'm sure he didn't, and I'm sure none of them did. Except that was what I thought.

Sullivan: 36:05

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

Thompson: 36:09

Well, I was. I don't know-- I'm just trying to remember exactly--

Sullivan: 36:18

I think it was the fall of '55 when he gave that talk.

Thompson: 36:21

Yes. I also have a memory of that meeting. 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. And I wondered just what they were doing in this meeting. And I found out afterwards that they were Bondi and I think it was Gold.

Sullivan: 36:47

Gold?

Thompson: 36:48

Yes.

Sullivan: 36:48

Yeah, Tom Gold. [laughter] You just didn't know that much.

Thompson: 36:52

I just didn't know that, no. That was another little interesting thing that I remember.

Sullivan: 37:00

I'm still struck by the fact that the intensity interferometer had revealed that Cygnus was perhaps a double. Anyway, it modeled as a double basically, and it was asymmetric in its distribution. And apparently, you weren't worrying about that too much in your longer and longer baselines.

Thompson: 37:19

The feeling was that you had to resolve them. As long as you couldn't resolve the source, there didn't seem to be too much point in worrying what direction you were-- it's quite true. Maybe you couldn't resolve it East-West. Maybe you would have done North-South, but we had a limited number of places we could go to.

Sullivan: 37:44

Right. And you had several sources also.

Thompson: 37:46

Oh, yeah. We had about a dozen. So they wouldn't have all resolved at the same angle. So it was kind of a Monte Carlo situation.

Sullivan: 37:56

How were these guys then chosen?

Thompson: 37:59

Oh, they were from Hanbury Brown's paper, and they were the stronger ones in it.

Sullivan: 38:05

And they were the ones that had survived, obviously, in terms of still showing pretty good results?

Thompson: 38:08

Yes, that's right. And as I said, we found practically no sources, I think, except Cygnus and Cassiopeia which resolved out nicely at intermediate baselines. We either couldn't get the antennas close enough together or far enough apart.

Sullivan: 38:25

And so then once again, as much as you can remember about how you felt at that time, in 1955 when you had this collection of a dozen sources a few arc seconds or less than that in size. Did this seem to prove to you that, conclusively, they must be outside the galaxy, very distant sources, or were you sort of open as to their nature?

Thompson: 38:45

Well, they had been-- they were …. Ryle had shown that these types of sources were more isotropically distributed. So it was generally thought at the time, they were very close to the Sun or else they were right outside the galaxy. And I think it seemed very unlikely that they were very close to the Sun since there were no optical counterparts of them.

Sullivan: 39:12

However, this made for tremendous luminosities, of course.

Thompson: 39:15

That's 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: 39:33

And you wouldn't see them on the sky survey or in the Palomar photographs, even, and that they--

Thompson: 39:40

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

Sullivan: 39:54

So you were not thinking of radio stars, really--

Thompson: 39:58

No.

Sullivan: 39:58

--in your mind, as you worked on these things.

Thompson: 40:00

No. Because, as I said, that summer of '72, Baade and Minkowski identified Cygnus, Cassiopeia, the Crab, and there was nothing that went with stars.

Sullivan: 40:12

Let me ask you about this '57 paper in Observatory. It's been said that this was a key paper in the sense that, 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 the field at that point, or is it only in retrospect that one goes back and says that they had isolated these sources?

Thompson: 40:41

Well, the experiment didn't stop when I left Jodrell. Morris had joined the group and-- I said earlier, didn't I, that Rowson joined the group. In fact, he didn't right away-- Rowson came in and did another experiment using an interferometer at 10 centimeters wavelength. And it wasn't until he finished that and got his PhD that he joined Palmer. And that was after I had left. But Morris joined about the time that I left. But that experiment went on.

Sullivan: 41:20

So this was just a way station, really. Are you saying then in longer and longer baselines?

Thompson: 41:24

Yes. Well, I was essentially responsible for building and setting up the first equipment in that interferometer experiment which continue and I think you could say is continuing in--

Sullivan: 41:40

In a sense.

Thompson: 41:41

--a better-- rather, evolved form now at Jodrell Bank.

Sullivan: 41:45

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

Thompson: 42:04

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

Sullivan: 42:26

But the particular value of a few arc seconds, did you look upon that as being significant? For instance, you were saying drawing a comparison with Cygnus A even if ….

Thompson: 42:35

Yeah. I think we did, yes. Thinking in those terms, yes. And if they turned out to be small, then they would indeed be objects with somewhat more remarkable properties of Cygnus.

Sullivan: 42:49

So you might not have been surprised if they'd all begun to resolve at that point.

Thompson: 42:52

That's right.

Sullivan: 42:53

--just Cygnus A is--

Thompson: 42:54

That's right.

Sullivan: 42:54

--further away.

Thompson: 42:55

That's one thing we might have thought, yes.

Sullivan: 42:58

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

Thompson: 43:05

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, what-- and that set us onto 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 the-- no, let me get this straight. We used our same electronics, but we used two different antennas. There was one on the top of the generator house at Jodrell, and we generated our own electric power and an antenna which had the property that you could rotate it around its own axis. It was about a 20-foot paraboloid and--

Sullivan: 44:11

I think it's still up there if I remember from a couple of years ago.

Thompson: 44:13

You're probably right.

Sullivan: 44:14

It's a dish on top of the generator.

Thompson: 44:15

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

Sullivan: 44:48

Who was this Russian? Do you remember?

Thompson: 44:50

Well, wait, I'm looking in my--

Sullivan: 44:52

This was in connection with synchrotron theory, I suppose.

Thompson: 44:54

Yes, well, I'm looking at the paper in which we wrote it up. And there's this, Dombrovski -

Thompson: 00:00

I don't 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 to a few percent. But that wasn't interesting.

Sullivan: 00:21

I think you're right. I don't remember any earlier experiments along those lines.

Thompson: 00:24

Well, I think Cambridge had done it.

Sullivan: 00:28

On radio sources also?

Thompson: 00:29

I'm 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: 00:42

I just don't remember.

Thompson: 00:45

It said the only published experiments appeared to be those of Ryle and Smith, who examined the intense sources of Cygnus and Cassiopeia with an interference polarimeter.

Sullivan: 00:55

So, they only looked at the two biggest.

Thompson: 00:57

Yeah.

Sullivan: 00:58

Now, what was the feeling as to the emission mechanism of the radio sources that time? Was it sort of a big unknown?

Thompson: 01:08

Well, I think certainly after that 1954-- sorry, 1955 meeting, it was understood that it was synchrotron emission.

Sullivan: 01:18

But before that?

Thompson: 01:19

It was something of an unknown. Yes. Yes. Going back, polarization had just been discovered optically in the Crab. That was what was being talked about. And that was the reason why we look for it in the Crab.

Sullivan: 01:34

Was that one of the sources you looked at?

Thompson: 01:35

Yeah. We used Cygnus, Cassiopeia, and the Crab, were the three that we looked at.

Sullivan: 01:40

And Cas was known to be a supernova remnant. Well, no, that's not true. Its nature wasn't clear. It was a nebulosity, and that's with high velocities. But whether it was a supernova remnant, I think was under debate at that time.

Thompson: 01:52

Yes. I think you're right.

Sullivan: 01:54

Okay. Well, that gives me a good coverage of the products that you worked on at Jodrell. I might just ask one general question about the whole way Jodrell operated. It obviously was one of the leading radio astronomical centers in the early '50s. And to what do you attribute that, and what do you think was the key ingredients?

Thompson: 02:19

Well, the British got off to an early start in radio astronomy, and of course, so did the Australians. I think it was-- well, due to Lovell’s 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 280 [ed. 250] ft dish was built for cosmic ray experiment to detect cosmic ray showers by radar.

Sullivan: 02:54

That was the initial--

Thompson: 02:56

That was the initial thing.

Sullivan: 02:58

--which the thing that Lovell had proposed during the war. The idea was something that he had proposed in a paper during the war.

Thompson: 03:03

I see.

Sullivan: 03:06

I'd forgotten that that was the original purpose. And was that experiment carried out?

Thompson: 03:08

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 MHz, and it wasn't very satisfactory. And Hanbury came along and used a much better feed, but the coaxial feeder and a much better receiver and was able to do a satisfactory sky survey. I guess it was partly because they got going so soon, I think. Partly because, well, the meteor radar stuff turned out to be a very fruitful field. And it lasted about 10, 15 years. But during that time, it was very fruitful. A great deal was learned about that high atmosphere from it. The observations were relatively straightforward with-- they were rather easy with the radar that had been developed during the Second World War. Cambridge came into it-- was never in the meteor field, but they came straight into the radio astronomy aspect. Ryle was probably more interested in cosmology and that kind of thing right from the beginning.

Sullivan: 04:33

Right from the beginning, you think so?

Thompson: 04:36

From earlier on. Maybe I shouldn't say right from the beginning, but I suspect that within a year or two of finding that he could catalog radio sources, I suspect that that was when he got interested in it.

Sullivan: 04:52

And so that would be around '50 or '51 probably?

Thompson: 04:55

Yes, because--

Sullivan: 04:57

The 1C was published in 1950. So, he was working on it '49 probably.

Thompson: 05:03

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

Sullivan: 05:06

Oh, yes, quite a bit in the late '40s. That's why I was wondering when you said right from the beginning. He started off working on the Sun for two or three years.

Thompson: 05:14

That's right.

Sullivan: 05:16

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

Thompson: 05:25

There were a lot of good people, I think, associated with things in those days. Hanbury Brown. There was a man called Clegg who wrote a small book on radio astronomy. 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. And I think he didn't get along too well with Lovell; somehow or other they didn't quite have the same style. And he eventually left. But he did an enormous amount of work in the early days getting the meteor radars going.

Sullivan: 06:14

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: 06:23

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

Sullivan: 06:34

So, this was an undergrad course that you were talking about?

Thompson: 06:37

Yes, oh, yes, that's right. Yes. Yes.

Sullivan: 06:38

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

Thompson: 06:41

That's right. Mainly, it's just few seminars and things.

Sullivan: 06:43

And so, what you learned was just from your own reading and the literature?

Thompson: 06:45

That's right. Yes. Yes.

Sullivan: 06:47

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

Thompson: 06:57

I think a mix of the two. And I might have just mentioned this as people coming to the United States from England. Gordon Little, who's now, I think, at Boulder, was the first one to come and then Alan Maxwell and various other people. I know I was third or fourth or something.

Sullivan: 07:18

Did you know J.B. Evans?

Thompson: 07:19

Yeah. J.B. Evans came after me. I knew him very well at Jodrell.  I think he came to Jodrell one year or two years after I-- one year, I think. And we were very good friends then. And of course, Dave Williams had gone to Canada. Dave Williams has worked with Marconi in Canada for a number of years.

Sullivan: 07:45

What about this outflux …?

Thompson: 07:47

Well, I guess we heard from people who'd gone and how interesting and what an exciting place United States was, and it seemed like quite an adventure to come over here. So, when I eventually got the opportunity, I came over, and I've never regretted it. Actually, what happened was when I left Jodrell, I thought it would be I was in 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, and I'd been there for about 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 possibly going over and joining him at Ft. Davis. So, I went and had lunch with him, and he asked me to think about it. And I decided that it would be an interesting thing to do, to come to the United States. So, I came in August 1957, and I stayed at Ft. Davis for five years.

Sullivan: 09:00

Is it fair to say that there really weren't that many opportunities to do radio astronomy in Britain and sort of saturated in terms of positions? And it was expanding in the US?

Thompson: 09:11

No, I could have stayed on at Jodrell if I wanted to. So, it wasn't--

Sullivan: 09:14

So, was the staff expanding then? To that extent at least, that there were some positions for the best students anyway?

Thompson: 09:19

Yes. Yes, it was. Well, you see the 250 ft dish was not quite complete when I left. But quite a lot of work was going around building instrumentation for it, and I could certainly have stayed and have work.

Sullivan: 09:36

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

Thompson: 09:41

Yes, that's right. But I guess I was young and felt the change of horizons would be in order.

Sullivan: 09:47

Okay. So, you came. Did you live in Ft. Davis immediately?

Thompson: 09:52

Yes.

Sullivan: 09:52

And what did you find there, and what did you begin working on?

Thompson: 09:56

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 it had this very complex antenna which would cover about three octaves of the radio spectrum.  They were all sweep frequency receivers. And I eventually 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 of the pieces and changed some of the mechanical things and put it together carefully and aligned it mechanically somewhat better than it had been to start with, and that became one of my annual jobs for the five years that I was there, taking the--

Sullivan: 11:05

A tune up, so to speak.

Thompson: 11:06

Yeah, taking the sweep frequency receivers to pieces and--

Sullivan: 11:08

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

Thompson: 11:17

I think it was kind of on the horizon, but we-- well, before I left Ft. Davis we had got a receiver that covered two to four GHz sweep-tuned using a backward wave oscillator which wasn't very reliable, incidentally. But the thought of doing that at the lower frequencies was a possibility - I believe those receivers are still running on the 28 ft dish. We eventually got two more off them which were 25 to 50 and 50 to 100 MHz. So, we scanned all the way from 25 to 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 were - one thing-- some of the main contributions of that particular work at Ft. Davis were getting a regular and reliable solar watch going - excuse me – to - so we had good catalogs of radio bursts and we could easily classify them into the four types, noise storms, slow-drift bursts, fast-drift bursts, continuum, and then finally the Type 5’s.

Sullivan: 13:00

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: 13:07

There was partly due to the other half of the day. I think they were monitoring fairly regularly. I don't think they had quite as good time coverages. We managed to get to about 95% time coverage.

Sullivan: 13:24

Not quite sure how much they had. They certainly were going well in those days. Yeah.

Thompson: 13:27

Yes. That's right. Well, another important thing was, of course, the United States had a number of very good optical solar observatories, and one really wanted good coverage during those periods where we could correlate flares with solar radio bursts.

Sullivan: 13:48

Which ones were you working with mainly, which observatories?

Thompson: 13:52

Oh, Sac Peak and High Altitude Observatory. Well, and then [Gale?] 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: 14:11

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

Thompson: 14:14

That's right. He eventually went to Australia and I've lost track of him. I don't know what's happened to him. We did a lot of work on the coincidences between different types of solar flares and different intensities with solar radio bursts.

Sullivan: 14:36

Right. 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 Wild's dynamic spectrograph?

Thompson: 14:47

The idea of using a dynamic spectrograph was - the actual receivers were an outgrowth, I think, of the military. 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 stuff.

Sullivan: 15:14

Or just radio communications.

Thompson: 15:16

Yeah. That's right. That is right. You could stop them and tune them to obtain the frequency.

Sullivan: 15:21

Right. And what were the improvements? I think you said some had better specs than Wild's spectrograph.

Thompson: 15:29

Yeah. We went to higher frequencies to 500 MHz. We had somewhat, I think, flatter frequency responses. Those were the main things. We had a somewhat better antenna. He had dipole things. We had a paraboloid to track with a very nice feed made by Henry Jasick.

Sullivan: 15:52

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 does it just matter that you were happy to be doing radio astronomy?

Thompson: 16:09

I was happy to be doing radio astronomy. No, I was always considerably interested in the techniques, as well as-- and I still am, of course. As well as the astronomy.

Sullivan: 16:19

Right. Okay. So now, let's get on to the scientific results that came out of-- out of this monitoring. What would you say were the primary-- the papers here seem to talk about correlations between cosmic rays and Type 3 and 4 bursts.

Thompson: 16:33

Yeah, we did some of that. Then, let me think. One of the things that we-- that we discovered was that there was a very strong correlation between Type 4 bursts and polar cap absorption phenomena. And we wrote that up in a little Nature article. I think the Japanese just beat us to getting that into print. They had discovered it, too.

Sullivan: 17:08

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

Thompson: 17:14

Yeah, I think perhaps so. Yes.

Sullivan: 17:16

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

Thompson: 17:28

I never regarded myself as a solar physicist in any way. And I think what we're doing this in a rather, in some ways, an empirical fashion. But we were interested in the-- in the quantitative/qualitative description of the bursts --

Sullivan: 17:50

And correlations?

Thompson: 17:52

-- and the correlations. And of course, we were interested in the theories about how the bursts – how the bursts were produced. Neither Maxwell nor I would ever have regarded ourselves as plasma physicists or theoretical physicists or theoretical astrophysicists. Alan was always trying to get Max Krook of Harvard, who was a great friend of his, to write a paper on the mechanisms of solar radio bursts because Krook had quite a number of ideas. But I don't think he ever did. Alan used to try desperately to get some kind of notes from Krook that he put in some of the papers that we wrote.

Sullivan: 18:41

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

Thompson: 18:43

I don't know whether he's Applied Physics or Mathematics.

Sullivan: 18:46

I just noticed here that it says in your-- Proceedings of the IRE paper in '58 that you have 10 times more sensitivity than anyone else, which means Wild’s sensitivity.

Thompson: 19:03

Yes. Of course, Fred Haddock started up at about the same time with Navy sponsorship.

Sullivan: 19:08

That's true.

Thompson: 19:09

And there was a certain amount of, I think, active feeling between him and Alan.

Sullivan: 19:14

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

Thompson: 19:16

The Air Force.

Sullivan: 19:17

The Air Force?

Thompson: 19:18

Through Sacramento Peak

Sullivan: 19:19

Oh, I see.

Sullivan: 19:19

It came via that way.

Thompson: 19:20

Ed Dennis [crosstalk].

Sullivan: 19:22

That's right. Menzel

Thompson: 19:23

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

Sullivan: 19:29

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

Thompson: 19:32

Let's see. There was something that just crossed my mind. Oh, well. Never mind.

Sullivan: 19:45

What would you say were the primary differences that you saw in the way radio astronomy was developing in the late '50s in the US, as opposed to England?

Thompson: 19:54

There was a great deal more emphasis to centimeter waves. We had all started in England at meter wavelengths and the US never really went through that. Partly because, I think, their centimeter wavelength technology was at a higher level and they kind of jumped in there.

Sullivan: 20:14

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

Thompson: 20:16

Yeah. Partly right, yes. That's right. That's right.

Sullivan: 20:20

But then, even though the NRL, even the NRL group, though, in the late '40s was working at centimeter waves. They never worked at anything lower than-- longer than 20 cm .

Thompson: 20:29

That's right. 21 cm was about the longest wavelength.

Sullivan: 20:34

And I guess that is generally true for the entire-- all US groups with only a couple exceptions. Okay, just to finish up. You were there till 1962, I believe?

Thompson: 20:43

Yes.

Sullivan: 20:43

And then you went to--

Thompson: 20:44

Stanford.

Sullivan: 20:45

To Stanford?

Thompson: 20:45

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

Sullivan: 20:54

A Cambridge-type of paraboloidal cylinder?

Thompson: 20:57

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

Sullivan: 21:09

For primarily solar work or--?

Thompson: 21:11

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

Sullivan: 21:18

What kind?

Thompson: 21:19

Growing array or an instrument which you could add to. And at that time, it wasn't so clear that you wanted resolution, but that you wanted-- he wanted a collecting area. And the thought was you had a long-- these long, trunk-like cylinders. So, you could add to it and make it a very large, square array. It would've been a meridian transit instrument largely.

Sullivan: 21:43

I see.

Thompson: 21:43

And so, I'm not-- as things developed, that wasn't really the way to go, but.

Sullivan: 21:49

And the money didn't come for that?

Thompson: 21:50

The money didn't come for it.

Sullivan: 21:52

And so, the effort at Stanford shifted in what direction, then?

Thompson: 21:55

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

Sullivan: 22:01

Even that early?

Thompson: 22:03

Well, let me see. And then, maybe I shouldn't say that early. Stan Zisk was there at that time. We had some 30 ft dishes. Maybe three of them? And those were put on mounts and they worked for 10 cm-- we did some 10 cm interferometry. That led into the 2.8 cm array that I mentioned.

Sullivan: 22:32

Okay. And just to finish off the-- your career. When did you become director of the VLA site?

Thompson: 22:44

Well, let's see. I joined NRAO in 19-- let's see. Well, I guess it was-- '72. So, I had worked-- I'd been there just five years, the beginning of this year, in January, '72. My title is Deputy Project Manager. I'm under Jack Lancaster. The exact date, which I will kind of dig out of my file--

Sullivan: 23:16

Well, it's not that critical.

Thompson: 23:18

'70 to '74.

Sullivan: 23:21

Well, thank you very much.

Thompson: 23:22

Yeah. You're--

Sullivan: 23:24

That ends the interview with Dick Thompson at the VLA in New Mexico on 1st, May, '78.