Interview with John G. Bolton, 15 March 1978

Title

Interview with John G. Bolton, 15 March 1978

Description

John Bolton, 1922-1993. Interviewed 15 March 1978 at Parkes, length of interview: 225 minutes.

Creator

Papers of Woodruff T. Sullivan III

Rights

NRAO/AUI/NSF

Type

Oral history interview

Interviewer

Sullivan, Woodruff T., III

Interviewee

Bolton, John G.

Location

Parkes, Australia

Original Format

Audio cassette tape

Duration

225 minutes

Interview Topics

Further details of early radio source work with sea cliff interferometers; development of cliff technique; galactic background survey and interpretation; world trip in 1950; personalities in Radiophysics (Bowen, Pawsey); 1955-1961 developing Owens Valley 2 x 90 ft and doing radio source positions, sizes, etc; optical identifications and relations with optical astronomers; philosophy on cosmology; plans for Parkes.

Start Date

1978-03-15

Notes

The interview listed below was either transcribed as part of Sullivan's research for his book, Cosmic Noise: A History of Early Radio Astronomy (Cambridge University Press, 2009) or was transcribed in the NRAO Archives by Sierra Smith in 2012-2013. The transcription may have been read and edited for clarity by Sullivan, and may have also been read and edited by the interviewee. Any notes added in the reading/editing process by Sullivan, the interviewee, or others who read the transcript have been included in brackets. If the interview was transcribed for Sullivan, the original typescript of the interview is available in the NRAO Archives. Sullivan's notes about each interview are available on the individual interviewee's Web page. During processing, full names of institutions and people were added in brackets and if especially long the interview was split into parts reflecting the sides of the original audio cassette tapes. 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.

Series

Working Files Series

Unit

Individuals Unit

Range #

8A

Transcription

Transcribed for Sullivan by Pamela M. Jernegan

Sullivan

Ok, this is continuing with John Bolton, after an intermission of 18 months or so, at Parkes on 15 March ’78. And let me just fill in a few things that we didn't talk about, about the first few years of radio source work and solar work as far as that goes. First of all, you mentioned to me that you actually started off at 60 megahertz looking for radio sources and had quite a bit of trouble there.

Bolton

Yes, Bruce Slee and I, late in 1946, built a 60 megahertz, essentially, polarization detector for work on the Sun. And this was looking at polarization of solar bursts, switching between left-handed and right-handed circular polarization. But we were interested in seeing if we could split up the general background of galactic radiation, and I guess we did two things wrong. First of all, we worked at the wrong frequency of 60 megahertz, where there is a tremendous amount of ionospheric scintillation. The other thing was we conducted a search looking at things like brightest stars, planetary nebulae, and that kind of thing, from which we could, perhaps by analogy with solar radiation, imagine reasons why there should be radio emissions.

Sullivan

Were these just taken out of Norton’s Star Atlas or something like that?

Bolton

That kind of thing. We didn't have an astronomical library at that stage of the operation. I guess Russell, Dugan, and Stewart [Astronomy] was our bible. Second edition.

Sullivan

However, you says this was actually for solar work that this receiver and antenna...

Bolton

Yes, the receiver was intended to provide experimental data on which D. F. Martyn would provide the theoretical background, looking at polarized noise storms.

Sullivan

That's right. Well, he had actually predicted some polarization in the quiet component, I think. Even in the quiet component of the Sun.

Bolton

Yes.

Sullivan

But were you sort of sneaking this in on the side, on the sly, then?

Bolton

Yes, we were sneaking this thing in on the side. In fact, [Joseph L.] Pawsey came and found us doing it and promptly decided that we should go back into Radiophysics and not continue any work at Dover Heights. I went to work with Gordon Stanley on building similar polarization equipment for an eclipse expedition, which Pawsey was going to take to Brazil.

Sullivan

For the May '47 eclipse, I believe it was?

Bolton

Yes. That expedition never took place, and when they missed the last boat, Pawsey came into the lab where Stanley and I were making this equipment and he said to me, "It looks as though we're not going to Brazil. If you can think of anything to do with this equipment, you can have it." As he went out of the room, he said, "If you can think of anything to do with Gordon Stanley, you can have him, too." So we began again, we took this equipment all out to Dover Heights and set ourselves up a solar observatory.

Sullivan

Now at 200?

Bolton

We had 200, 100, 85 and 60 megahertz equipment. And we actually observed the first of the Type II solar outbursts. I think in March of '47.

Sullivan

Why were you still working on the Sun? I thought you had now the green light to do non-solar work.

Bolton

Well, this was solar equipment, and we set it up to work on the Sun. And in February of '47, when we got out there, it looked as if it might be a very exciting period on the Sun because there was a big sunspot group developing. As a matter of fact, we saw it disappear from one edge of the Sun and reappear on the other edge, and we were getting absolutely nothing from it until it was almost on the meridian. And then one Saturday afternoon, I went back to Dover Heights and turned the antennas on for the Sun, and within five minutes we got the biggest signal we'd ever seen- it blew the 200 megahertz recorder off scale, and the recorders were only running at very slow speed. I switched the 100 and the 60 on to high speed on the recorder, turned down the gain, and we recorded. About two minutes later the 100 megahertz went off scale and then three minutes later the 60 megahertz. Now we couldn’t accurately time the 200 megahertz, but C. W. Allen of Mount Stromlo had the 200 megahertz patrol equipment, which Radiophysics had built, and we got the timing of the outburst on 200 from him. And Ruby Payne-Scott and Don [Donald E.] Yabsley had been working on the other types of bursts. We put all our data together in one letter to Nature.

Sullivan

Right, which came out in '47.

Bolton

Yes, well, we followed that sunspot through March and April. After the big outburst, we then got a noise storm on very high level. We got some quite interesting polarization work. But by mid-May, the solar activity had gone down to nothing. And Stanley had been working on trying to improve the sensitivity and stability of the receivers. And we started working the cliff interferometer again, looking for objects, looking to sea interference patterns. And given the earlier failure which Bruce Slee and I had, with the wrong frequency and looking for the wrong objects, we just started a purely empirical search. Just a blind search.

Sullivan

But now, actually, when you did that first search, had you gotten word of [James] Hey’s discrete source? I can check when that- well, you might have had a preprint though, that’s true. It was published in '46, but I don't remember more exactly than that. [WS: 17 August issue of Nature]

Bolton

While Slee and I were out at Dover Heights, that work did appear, and in fact, after we came back to Radiophysics, Pawsey went out and used some 60 megahertz equipment to look for the Cygnus scintillations. But didn't find them.

Sullivan

That's right. You mentioned that before and in retrospect, it's probably just because the ionosphere was quiet when he happened to go out.

Bolton

That's right. Yes.

Sullivan

So at that time, then, it was sort of in the middle of your search that you found out about Hey’s sources, as far as you can remember?

Bolton

As far as I remember, Slee and I had started work and we'd already been thrown off it, when Hey’s work was published. Pawsey went out himself to Dover Heights with 60 megahertz equipment to have a look at it, and couldn't find it. And so when Stanley and I started up again, locally Hey’s work was not...

Sullivan

Was in disrepute?

Bolton

Well, yes. We certainly didn't take any notice of it.

Sullivan

You mentioned that your interest was not really in the Sun, and yet when the Sun was active, you seemed to have been quite enthusiastic about working with it for a couple of months. Was it just that the quiet Sun bored you, but when it was active, that seemed to be sort of...

Bolton

Well, at that stage, of course we couldn't see the quiet Sun. The cliff interferometer, of course, resolved the quiet Sun out.

Sullivan

Yes, that's true.

Bolton

Stanley and I did, in fact, find the quiet Sun at low frequencies, eventually.

Sullivan

It had been recognized, of course, from Pawsey's correlation with sunspots and so forth. But it wasn't something that was easy to study.

Bolton

You see, we were at sunspot maximum, so it was dominated by active regions.

Sullivan

But anyway, it seems that your real interest was in the radio sources, and so you began a blind search, which I guess means starting at a slightly different azimuth each morning and seeing what you found. We covered this before when you said that, I believe, Taurus was the first and Centaurus was in there also, but you didn't recognize it at the time.

Bolton

It's hard to say. Before we found the Cygnus source, we had a possible detection of Centaurus at 200 megahertz. This would have been in May of '47. But unfortunately, our 200 megahertz equipment blew up.

Sullivan

Why was that?

Bolton

We had problems with the antenna and winds and so on, and the antenna got badly damaged. So we concentrated on the 100 megahertz. So probably, historically, Centaurus was the first object we found, followed by Cygnus. But in the literature, we give Cygnus as the first one and the Crab Nebula as the second one.

Sullivan

Yeah. I'm looking at the '48 paper.

Bolton

This was the order in which they were discovered at 100 megahertz, but, we’d probably had seen Centaurus at 200 megahertz before Cygnus.

Sullivan

I see. I'm looking at the 1948 Nature article and, indeed, the only '46 source is Cygnus and the other major ones are all '47. Now, let me just ask a couple of clearing up points about the things we discussed before. Namely, the fact that the refraction corrections that you were using were incorrect led to large errors in the positions you gave in this 1948 article.

Bolton

Yes.

Sullivan

However, the errors in the refraction corrections were not as large as 5° or 10°, the errors in the corrections were not that large.

Bolton

Oh, no. No.

Sullivan

Can you just tell me why this became magnified?

Bolton

Well, the sea interferometer pattern one interprets as the apparent position of an object at subsequent fringe minima, so what one gets a curve of is the apparent zenith angle versus time, which is related to the declination. But it's a very insensitive function, so if the slope is just a little wrong, a difference of refraction correction of, say, 20 minutes of arc between 0° and 10°, makes a declination error which- well actually I think it determined the cosign of the declination, so that if you have a declination near 0, it's a very large error. I think you'll find that our error in the case of Cygnus was only of the order of a degree, but our error in the case of M87, which is at declination of 12°, was the order of 10°.

Sullivan

It turns out to be worse for something near the equator.

Bolton

That's right.

Sullivan

That's rising perpendicular.

Bolton

Ah, yes. But it's a cosine declination term, which is insensitive near zero.

Sullivan

Okay. And the reason that this incorrect correction came about was because of the lack of recognition that radio bursts do not coincide necessarily with the optical active region.

Bolton

Yes. It so happened in Pawsey's original experiments that the spots which he'd observed were generally on one limb of the Sun, and so the error was always in the same sense.

Sullivan

And you say that Pearcey’s theory was based on this observation?

Bolton

Yes, Pearcey’s theory, indeed, fitted the Pawsey observation, but the Pearcey theory was based on a smooth ionosphere.

Sullivan

Right. Did he twiddle his parameters in order to get it to fit the Pawsey observation? That's what I'm trying to get at.

Bolton

Well, it was an order of magnitude calculation. I mean, the actual densities and the electron distribution in the ionosphere was not very well known.

Sullivan

Okay.

Bolton

And, yes, I think numbers could be adjusted to fit the Pawsey observation. There was a lot of scatter on the Pawsey observation, of course, so...

Sullivan

Now, if you hadn't had that theory, then what would you have used for your refraction in any case?

Bolton

I guess if we hadn't had that theory, we would have used optical refraction, not knowing any better.

Sullivan

Okay.

Bolton

We found, of course- immediately when we went to New Zealand, when we did observations of the east coast rising, discrepancies immediately came up. In fact, we had some azimuth resolution in our antennas that we took to New Zealand.

Sullivan

They were larger?

Bolton

The initial Sydney observations only had the resolution of a single Yagi, but we had several Yagis on the New Zealand experiments, and of course when it came to west coast observations, the first observation that we did of the Crab Nebula, the objects had set...

Sullivan

You couldn't find it at all?

Bolton

We didn't even start it.

Sullivan

Was that clear? You must have first thought that something wasn't working in the equipment.

Bolton

Well, I think our first indication that there were things that were horribly wrong was the observation of Cygnus which we had hoped to see through transit and down the other side. And our declination for Cygnus, I think, was 1° or 2° further north.

Sullivan

That's right, 1°.

Bolton

And, of course, the interference pattern just went on and went on. The lobes were getting longer and longer, but they weren't stopping as they should have done if the Cygnus declination had been 43° and not 41.5°.

Sullivan

I see, so then you said, "Well maybe all these other sources are off, too."

Bolton

Yes. I think it became clear to us on the east coast that we had some moderate errors in our initial positions, which as soon as we went to the west coast, we realized they were dramatic errors.

Sullivan

It seems a little curious to me that you took along a larger antenna on this expedition to New Zealand than you had at your home field site.

Bolton

Well, we got some funds to build this second- in the Sydney experiments, we used two Yagis- one on top of the other, so that it narrowed our vertical pattern, not the horizontal patterns. For the New Zealand experiment, we took six Yagis- two vertical and three horizontal. We later cut down to 4 because the spacing- we’d got them a little close together initially.

Sullivan

Did you then bring that back and use that...

Bolton

Well, the reason for building a new set of equipment was that we wanted to find out whether the scintillations of the sources were genuine or not, from a spaced antenna experiment. Bruce Slee, who in the meantime had rejoined the group, operated the Sydney equipment and we operated the New Zealand equipment. We actually did some solar observations to see whether solar bursts correlated. And as they did, and the radio source scintillations did not, this was the proof that the scintillations were, in fact, scintillations and not inherent in the source.

Sullivan

And this work was done in ‘48?

Bolton

‘48, yes.

Sullivan

Right. Now usually in the accepted wisdom, credit is given to "Little and Lovell" and "Smith," a couple of papers in Nature, for finally establishing that the scintillations were ionospheric. However, this work was done before but published much later, I believe.

Bolton

It was done before and the Cambridge group was well aware of our results. In fact, I had suggested that Ryle do the experiment.

Sullivan

Just as a confirmation, you mean?

Bolton

Well, we had spaced antennas, 1,500 miles apart. It was very difficult for us to get spaced antennas, certainly using the sea interferometer with a realistically small spacing. Because the coast of New South Wales runs in such a direction that for every hundred miles you go north, you only get 1 mile or a few miles of extra spacing projected to the north between the antennas, so it was clearly not an experiment for us, whereas Jodrell Bank and Manchester could easily have done the experiment- they had much bigger antennas than we had- both [A. C. Bernard] Lovell’s and [Martin] Ryle’s arrays were at least two orders of magnitude better than us- so they had no problem with signals.

Sullivan

I see what you're saying.

Bolton

And in fact, in the papers by Little and Lovell and Ryle and Smith, you'll find that it says, "Information from Pawsey".

Sullivan

That's right. So the idea was that you had established that there was no long baseline correlation, but there still might be something on a 50, 100 kilometer sort of...

Bolton

No, I mean the experiment we suggested was to find the scale of the correlation.

Sullivan

At some point it must correlate.

Bolton

Yes, at some point it must correlate. And it was one of those very unfortunate things of history that I kept writing to Ryle and saying "How is it going?" And he didn't let me know the experiment was being done and he didn't even let Lovell know that I'd suggested it. In fact, at the 1950 meeting of URSI [International Union of Radio Science] in Zurich, Lovell made a public apology.

Sullivan

Was that '50 in Zurich? Which meeting is that? I'm not familiar with it.

Bolton

This is URSI in Zurich.

Sullivan

And only two years later it was in Sydney in 1952?

Bolton

Yes. The URSI at that time was every two years.

Sullivan

I see. That's interesting.

Bolton

In fact, they didn't change over to three years until I think, 1960.

Sullivan

So you were not in correspondence with Jodrell Bank at this time?

Bolton

No. I actually went to England in 1950 and the first thing that greeted me in the Scientific Liaison Office in Australia House was the Nature with the articles in it. Relations with Cambridge were very strained.

Sullivan

And it was going to take a couple of months to get to Australia, yeah.

Break in the tape

Sullivan

Just looking at the first few papers on radio sources which you published, it seemed to me that the idea that you had as to the origin of these radio sources was that it was the integrated effect of millions of these that was making up the galactic background. It just happened to be that these were the strongest, in what we would now call the luminosity functions. Is that right?

Bolton

Yeah, I think that was the initial approach. And certainly, the identification of the Crab supported this, though the few galaxies we got obviously made us wonder...

Sullivan

Well, one of them you were not quite willing to believe it was a galaxy because you felt...

Bolton

There was no evidence that it was at the time.

Sullivan

But even for M87 you say it has never been resolved into stars, so you're really being devil's advocate there.

Bolton

Yes. Well, one of the interesting things on this was when we got these first three identifications, the Crab was very likely. The others were somewhat lucky in that they were relatively nearby us; if they'd been a lot further away, of course, we'd never have gotten them, and we didn’t, in fact, get Cygnus with the accuracy required.

___

Sullivan

John Bolton on 15 March ’78.

Bolton

Well, during the long nights we spent keeping a recorder pen on scale at Dover Heights, I had been educating myself. I'd read twenty years of the Astrophysical Journal, twenty years of Monthly Notices, and that kind of thing, anything I could get hold of. And when we got these first three identifications, the people who sort of stood out in my mind were [Rudolph] Minkowski and Linblad- the elder Linblad- and [Jan Hendrik] Oort. And I wrote to all three, giving the results, you see. Now Minkowski and Oort had both written papers on the Crab, and I remember getting a very enthusiastic letter back from Oort with two or three pages on his ideas on the Crab Nebula and that kind of thing. There was just one line at the end of the paper commenting on the other two identifications. Jan said, "Of course, there are an awful lot of galaxies in the Virgo cluster." But I mean, the thing about Oort was that he still kept that in the back of his mind; and then when he went next time to Palomar, he persuaded, I think, Baade to use the 200 inch telescope to take photographs of M87 with all different filters.

Sullivan

I think you did mention in the paper- no, you didn’t. When did it come to light to you that it had this peculiar jet? Because that had been known back in 1917 or so.

Bolton

Yes, it probably had, but Oort, I think, had [Walter] Baade take a whole new series of plates from Palmar, and I remember Oort writing to me from Palomar, sending an ultraviolet picture showing the jet. I certainly wasn't aware of the earlier reference. Oort may well have been.

Sullivan

Well, he probably wasn't. I think it was pretty obscure.

Bolton

Yes. Although he dismissed the identification in his letter to me, he had enough interest to push it.

Sullivan

Did you get any reaction from the other people you wrote to?

Bolton

Oh, yes. I wrote to Minkowski and got a letter back from Baade. I wrote back to Baade and got a letter from Minkowski. In fact, for quite a number of years our correspondence went that way. If you wrote Baade you got a letter from Minkowski.

Sullivan

Anyway, what did they say?

Bolton

I forget. I mean Rudolph wrote to me. I think he was stimulated at the time to take another or try to obtain another spectrum of that central star, which of course, later became the pulsar. And he- or Baade said in this case, "Any other positions you have we'd like to have them and try to follow them up." Of course, the Puppis position which we gave him a year later enabled the identification of that supernova remnant.

Sullivan

Right, but even right from the very earliest, in 1947 or 1948, when you first contacted them, they had a high interest?

Bolton

Yes.

Sullivan

It wasn't only after the Cygnus A business...

Bolton

No, oh no.

Sullivan

That's interesting. Well, looking once again at this paper, I notice that the title of it is "Positions of Three Discrete Sources of Galactic Radio Frequency Radiation."

Bolton

Yes.

Sullivan

Which, I think, is telling also.

Bolton

Yes, of course, the radiation in those days was known as "galactic noise," or "cosmic noise."

Sullivan

But even though you had two reasonable identifications with extragalactic, you still wanted to call them galactic?

Bolton

No. There were two kinds of noise - solar noise and galactic noise...

Sullivan

I see.

Bolton

Under the general heading of cosmic noise.

Sullivan

Okay.

Bolton

These were more galactic than solar.

Sullivan

Now, going to the paper with Stanley in which you give a precise size for Cygnus A and the declination was 1° off- let’s see, I guess I didn't have any specific questions on that one. You had a follow-up paper in the Australian Journal of Scientific Research on that with much more detail. Ah yes, there was a thing where you broke the Cygnus A radiation up into two components, the variable and the steady. And you said there’s a steep slope on the variable, which makes sense. But for the steady slope, it seemed like you had a peak at 100, so that you give a sketch of a turnover at around 100 megahertz. Do you remember how this might have come about?

Bolton

Well, I think if you add those you get a steep slope. This is just the sort of average characteristic of the scintillating component of that period.

Sullivan

I see. So it was just an incorrect subtraction of the scintillating components.

Bolton

No, I don't think it was an incorrect subtraction of the scintillating component.

Sullivan

Okay, I’m...

Bolton

At 60 megahertz it's all scintillation, so there's no steady component. So it must peak. At 200 megahertz you see no scintillation, so it's all steady.

Sullivan

Yes.

Bolton

At 100 you see half scintillation, but the 100 total has gone up much more than the 200. And then at 60, it's all scintillating, so the steady component must go down, by definition.

Sullivan

In fractional amounts, yes, but not necessarily in the absolute amounts.

Bolton

Yes, the absolute amount goes to 0, or it is going to 0; it's all scintillation, let’s say, at 40 megahertz.

Sullivan

Oh, I see. I see. Now the picture is coming to me. Right. So basically, it's a confused concept - well, what were you thinking at this stage? You hadn't yet gone to New Zealand, I believe.

Bolton

No, oh no.

Sullivan

So what were your thoughts on the cause of this scintillation? I think in the paper you're very noncommittal.

Bolton

I think Bruce Slee certainly always thought it was scintillation.

Sullivan

Ionospheric?

Bolton

Yes.

Sullivan

You say, "The question of its nature is left open for the present," but what were you thinking in your own mind? Can you put yourself at that time?

Bolton

Well, I don't think we knew. By analogy with the Sun, I mean, it just looked like another Sun. The Sun does exactly the same thing.

Sullivan

Right.

Bolton

The variable component is something which is much stronger at low frequencies. So I guess it was the solar analogy which...

Sullivan

And that would also put it not that far away from the solar system, if you scaled it down.

Bolton

No. But, we didn't know. The New Zealand experiment was designed to find out.

Sullivan

Well I've just heard people say that it was quite clear to them that around 1946-47 that it must be ionospheric, and I've been a little bit puzzled by that whether they were just sort of biased in their mind or whether they really had evidence of that.

Bolton

Who would you say?

Sullivan

I'm afraid I really can't remember to name names, but I think really there wasn't that much clear evidence but they just always assumed it was ionospheric and it was a matter of someone going out and proving it.

Bolton

No. I think we had no evidence, and as I say, the varying component got larger as one went toward low frequencies, which was exactly the same thing the Sun did. And we knew that the solar variations were intrinsic; spaced aerial experiments had been done on the Sun. We naturally took the spaced-aerial experiments on the Sun as our control experiment for the scintillations.

Sullivan

That makes perfect sense. Moving on to the paper by yourself [Sullivan: Nature, 1948], that's one question I wanted to ask you. The others had been in association with Stanley and/or Slee, I was wondering how this one came to be only by yourself. Do you remember how that came about?

Bolton

Oh, I don't know. I was sticking my neck out a bit. I think that was one thing.

Sullivan

I didn't ask Bruce that, maybe I should have.

Bolton

Well Bruce wasn't working with us at that time.

Sullivan

Oh, he wasn't yet with you? He came in for the first time often with these identifications...

Bolton

Yes. Now he wasn't actually part of the identification team. It was Stanley and I who did the work, but we did use some of Bruce's Dover Heights measurements to clear up one or two points on that. I think in the case of the Cygnus experiments, Stanley and I had actually worked together. I mean, we sat up at night together; we'd gone to various places to see if we could get a high cliff together. We’d done that all together. But the major observations on those other sources and so on, essentially were all my observations. Stanley at the time had gone back to building equipment and that kind of thing. So it was essentially my own sitting up at night and so on which got those.

Sullivan

And like you say, it was a bit of a risky sort of paper.

Bolton

Yes, but others were not really involved in the observations for it. I mean the point of that paper is to say, "Well, the first one is not unique; there's a whole class of these things. We’re starting a new branch of astronomy."

Sullivan

Yeah, they're all over.

Bolton

They're all over, that's right. But then, of course, Stanley was in on the New Zealand position-finding observations and Bruce did some of the backup observations from Dover Heights. He'd been in on the scintillation part of it, very obviously. So the next paper was by the lot of us. In a way, of course, this was a departure from tradition, by including those people in papers.

Sullivan

Technicians, basically.

Bolton

Technicians in papers.

Sullivan

Yeah. Other people have mentioned that to me. Was this a policy of [E.G. "Taffy"] Bowen's or how did this come about?

Bolton

No, it was a policy of mine.

Sullivan

It's more common today.

Bolton

Yes, very common today.

Sullivan

But at that time, it was unusual.

Bolton

I'd done a lot of experimental flying and that kind of thing during the war and I always recognized the people who kept my airplane together. It seemed to me that...

Sullivan

That they should get proper credit?

Bolton

Yes. And it did become a Radiophysics model.

Sullivan

I know that. Looking at this Bolton '48 Nature article, it seems like, indeed, you have been looking at some basic astronomy texts and reading journals, because you speculate on what the nature of these "radio stars," as they came to be known, might be and I gather, couldn't make them main sequence because the Sun wasn't... Well, that's not true; the Sun was like Cygnus anyway, but the others were not scintillating so much, so you said that they’re either post-main sequence or pre-main sequence, maybe like a planetary nebula or a contracting star. Is my reasoning right there? Did you just sort of take the other two kinds of stars that were known?

Bolton

Yes.

Sullivan

Let me ask you another question. Were you unusual in this sort of methodical past-twenty years of Astrophysical Journal and Monthly Notices? Were other people doing this? I haven't heard anyone else talk about how they learned what they had to for their projects.

Bolton

I think I would be, yes. I think an effort was made to go into solar physics. This was how Steve Smerd got his start. Pawsey one day said he'd like Steve to give a lecture on the basic physics of the Sun and solar atmosphere. Thirty years later, Steve is still preparing his lecture.

Sullivan

Yes, other people boned up on the particular area that they were in, but as sort of a general education, a self-education, I haven't heard anyone mention that. Alright, now the other paper that I have a copy of here is your paper on Taurus A with Stanley, and you call it in the abstract one of the "minor" discrete sources of galactic radio frequency noise. I suppose "minor" refers to the fact that it's a small fraction of the galactic radiation, but I thought that was sort of funny. Why in Table 2 do you give times in units of minutes and fifteenths a minute?

Bolton

Because that was our measuring.

Sullivan

On the strip chart or something?

Bolton

Yes.

Sullivan

I see.

Bolton

Minutes and fifteenths of a minute is approximately four seconds.

Sullivan

One minute of arc, yeah. Somehow that one got by the referee. That's rather non-SI unit.

Bolton

That was the smallest sensible unit. Compared to the scatter, which refraction and everything else gave us. I think it was essentially the minute of arc. After all, you made your own rules in those days.

Sullivan

Yes, that's true also.

Bolton

One of the biggest difficulties I ever had was getting the concept of antenna temperature.

Sullivan

Why was that?

Bolton

Now it's a very recognized concept, but [Kevin C.] Westfold and I wrote a paper - well, I guess, Burgess was one person.

Sullivan

Right, he had a paper during the wartime [Sullivan: also 1948].

Bolton

Westfield and I shared that antenna temperature, in fact was proper physics.

Sullivan

What about the [Robert] Dicke paper in ‘46? Was that not part of your knowledge at that time?

Bolton

Oh yes, the Dicke paper was. The temperature concept had sort of been used loosely, and we showed that it was valid physics to use antenna temperature.

Sullivan

This was in an internal lab report?

Bolton

No. This was in one of the papers we produced.

Sullivan

It's in one of the Bolton-Westfold series, I see. [Sullivan: Paper I, 1950]

Bolton

One of the Bolton-Westfold series. I mean Westfold was somewhat pedantic and I sort of convinced him that this was reasonable physical concept and Kevin produced the mathematics to show that it indeed was a valid physical concept. But it wasn't in general use. The Americans actually took up the concept of antenna temperature when they came in the vast numbers [Sullivan: in the late 1950s].

Sullivan

Perhaps because they were working at higher frequencies. For instance, the NRL group and so forth. Perhaps it works there in a little more clear-cut fashion. Let's see now, that takes care of all of the papers through 1950; however, perhaps you should tell me some more about your trip to New Zealand and so forth. For instance, you mentioned to me before we started recording about how you didn't get any useful Cygnus A position in New Zealand. Why was that?

Bolton

I am not quite sure. It was probably the time of year at which we were observing and the interference from Spread-F. What we'd hoped to do with Cygnus was in fact to count the fringes to transit to get a second handle on the declination. Fringe separation in New Zealand was roughly 1/4°.

Sullivan

You were on a higher cliff there.

Bolton

Yes. But unfortunately, what happened was that near transit the fringes get very long, and after transit, even though we had a clear horizon till the second point, I think the ionosphere broke up or interfered with the pattern so badly that we didn't in fact, get very good data. And when we moved across to the west coast, we again didn't get very good data, whereas the data on the Crab, on M87, and on NGC 5128, which were at different times of the day, were really good. You see, Cygnus was transiting somewhere around midnight which is the local maximum, and transiting setting was nearly midnight and this was the maximum Spread-F, whereas the other objects were in times where spread-F scintillations were very low.

Sullivan

So this was useful for the correlation of ionospheric stuff, but not for source positions?

Bolton

Yes, you see, two problems - one is spread-F, which has sort of local maximum at midnight and sporadic-E, which had local maximums at midday. Now it so happened, I think, on the Crab and M87 that we were clear of midnight and midday and Centaurus wasn't so good. But Cygnus was rather ruined; in fact, we never published our Cygnus position. We knew it was closer to 42° than 43° but weren't able to really pin it down. In fact, I don't think we were ever able to successfully identify the second fringe.

Sullivan

I see. And you went to two different sites in New Zealand, I believe.

Bolton

Yes.

Sullivan

What was the purpose of two sites?

Bolton

Well, from the first site we had, theoretically, a view of Cygnus right through.

Sullivan

Basically north.

Bolton

Yes, north and east. And this gave us also rising patterns of the Crab, M87 and 5128. We had to move over to a west coast site to get the setting pattern for the other three objects.

Sullivan

Okay. The survey by Stanley and Slee was the first major survey to come from the Australian work, published in 1950. Once again I might ask why you were not an author on that one?

Bolton

What was the date on that?

Sullivan

’50. It was submitted in November of 1949.

Bolton

The work on that was in fact, just as much due to Kevin Westfold and me, as it was to Stanley and Slee, and this was an occasion where we simply split publication between- four names on paper seemed a little large, so Westfold and I took the general over and published it and Stanley and Slee took the source population and published it.

Sullivan

But it was really all four of you working on it?

Bolton

Yes, it was all four of us working on the same thing; in fact, I think you'll find acknowledgments backwards and forwards when it came to the sea-interferometer or phenomena Bruce Slee and I wrote that. When it came to work on scintillation, I think; Slee and I also wrote that up.

Sullivan

Okay, I see.

Bolton

When it came to try to model the galactic background, it was Westfold and I, so I mean, the splitting up was just...

Sullivan

Right. So this survey then was a complete southern sky survey?

Bolton

Not complete, because it didn't cover the southern polar regions. They don't rise and set.

Sullivan

Okay, everything you could get from the sea-cliff interferometer anyway, and you have 22 sources in here, most of which turn out in hindsight to be legitimate.

Bolton

Well, a larger fraction than was customary in those days.

Sullivan

Well, yes.

Bolton

It was customary in those times.

Sullivan

What were your impressions at this stage of the development of radio sources where, this was just about exactly the time of 1C survey which had about fifty sources, and so you probably had a pre-print of that by this time also. What were you thinking about the nature of these radio sources?

Bolton

About the nature?

Sullivan

Was this telling you anything when you could begin to do some statistics as to where they were located in the sky and the distribution and intensity, or was this too early?

Bolton

No, I think at that stage it was too early. We, I think, were more- I mean this was just, we'd done this work and here, we pass it on for general scientific...

Sullivan

Okay, so you didn't have any great conclusions to make.

Bolton

No this was toward the end of how far we, we'd gone as far as we could go without new equipment. This was done with the 9 Yagi array, which Westfold and I did the general background survey with, and our next stage was to build a rather larger sea interferometer, which had, I think, a 6 x 2 Yagi system with azimuth resolution, higher azimuth resolution in this case. And...

Sullivan

And somewhat more sensitivity?

Bolton

Somewhat more sensitivity. And then, that paper, I think, which came out in 1953 did have some statistics, I think that might have been me, Stanley and Slee.

Sullivan

1954 - 104 radio sources at 100 megahertz?

Bolton

That's right. This is the first time we mentioned log N- log S, which was anomalous.

Sullivan

Something I've never actually done or even thought about is the cross-correlation of this survey with the 1C, Ryle, [Francis Graham] Smith, and [Bruce] Elsmore, I believe it is. Did you do that in region of overlap?

Bolton

I don't think there was any correlation.

Sullivan

Even at this early stage, you mean, the pattern was set? I'll have to do that. I just don't remember any comments on that, by either side at that time. But do you remember doing it at that time? I would think it would be an obvious thing to want to do.

Bolton

I remember noting that the source in Ursa Major was exactly twelve hours different from the source in Cassiopeia and the same declination.

Sullivan

Well, from the Nature [Sullivan: 1948] article. They'd gotten rid of that by the time they published the 1C.

Bolton

That was the only thing. No, what was the date of that one?

Sullivan

1950. The other was published that same year.

Bolton

Of course, after that Westfold and I got busy doing, well, what can we find out with an interferometer, how accurate is it? That was when we started building the 80 foot dish in the ground.

Sullivan

The hole in the ground.

Bolton

Going to higher frequencies.

Sullivan

Okay, let's talk about that hole in the ground, first of all, where does that idea come from?

Bolton

Well, I suppose it was me.

Sullivan

But I mean, have you heard of the concept somewhere else or you just said well this is something that's sort of an obvious thing to do?

Bolton

No, I think it's an obvious thing to do. And it really came out of Westfold's and my work- that one has to get some primary gains into the antennas, and we built this as an experimental antenna at the same time as Stanley started to devote his attention to how to get sensitivity at high frequency.

Sullivan

I see.

Bolton

We actually worked the antenna first at 160 megahertz but it was intended to work at 400.

Sullivan

In terms of the accuracy of the surface.

Bolton

And that dish was and the receiver were really the prototypes of the Caltech dishes.

Sullivan

I see. They are similar size, that's right.

Bolton

And the receiver technology was taken directly from a Caltech dish.

Sullivan

You chose this over a 30 foot steerable thing which might have been feasible at that time, at least as a transit instrument, simply because you wanted to have that additional gain?

Bolton

Additional resolving power.

Sullivan

Oh, you wanted the resolution. Tell me, while we're recording here, what you told me before about the colloquium, the talk, that you and Westfold gave at this time.

Bolton

Well, I guess that must have been a talk somewhere around 1951. We gave a talk which we entitled "Discernibility and Detectability" and showed that in fact, one's ability to detect objects far exceeded one's ability to discern objects. And one of the things we got laughed down at was proving that with our 17° 9-Yagi ray, although we could detect many hundreds of sources, in fact, we could only sort out what corresponded to one source per four or five beam areas, and we were really laughed at for that.

Sullivan

And what was the point of disagreement?

Bolton

I don't think anybody understood. I mean an interference pattern is something which is terribly real and terribly false. That is to say, the sum of n sine waves is still a sine wave.

Sullivan

Yes.

Bolton

And that is the thing which we could not get across- that one cannot resolve that.

Sullivan

That the interpretation is laden with difficulty, yes.

Bolton

We found this out empirically, in our crossed two-aerials on the cliff interferometer and we could move one of the aerials with respect to the other. And, although, we would get interference patterns which were cross patterns for sure, and we could think we could sort out sources, as soon as we went to another spacing we’d sort out a different lot of sources.

Sullivan

Right. And this was already clear though from your first few sources where you had a couple that happened to be near each other in the sky and the two patterns were beating, and I guess it wasn't quite so clear to the solar people because they only had the one big source. So that's an interesting thing that you had there in the light of the late '50s with the controversies over confusion and so forth...

Bolton

Yes. Well, in this 1954 paper we gave 100 sources and so on and we had found the steep slope of the log N - log S and at the end of that paper, I dismissed it as the kind of thing that happens with clustering. Because if you look at the log N - log S in the Shapley-Ames catalogue, it’s dominated by the Virgo cluster and gives you a steep log N - log S.

Sullivan

So you mean we just happen to be located in a region where there was a...

Bolton

Yeah, well I had no inclination- I had to throw in some suggestion and clustering was one of the things that could clearly do it.

Sullivan

Are you talking about the concept that we have to be located somewhat in a hole so that there are fewer strong sources.

Bolton

It's the same thing.

Sullivan

The same thing that came up later - that Hoyle came up with and so on. But now by that time were you thinking of these sources as being primarily extragalactic?

Bolton

Yes. Yes, I was.

Sullivan

When did that changeover take place? Was it Cygnus?

Bolton

No. I think it was purely theoretical. In fact, I remember at one meeting we had in Sydney when Sir Harry Massie was there and wanted to hear about radio astronomy and we had a joint meeting with Stromlo and I remember having an argument with [Richard] Woolley. And I said that I felt that these things were galaxies, because I couldn't see the energy density being produced in a stellar atmosphere to give these signals- they had to be minutes of arc across. In other words, the source temperature, even though I didn't know anything about synchrotron radiation or what the limits on brightness temperature were, I felt they had to have a large emitting body, but this was just a...

Sullivan

Even though, of course, that meant their luminosity became tremendous. But when you go to a galaxy, you have more resources, also.

Bolton

Yes.

Sullivan

And that would be about when?

Bolton

I mean, at that time we recognized that all the galactic radiation wasn't going to break up into point sources, I think.

Sullivan

And what was the basis of that?

Bolton

Simply that it didn't...

Sullivan

With higher resolution it was still...

Bolton

Yes, there was an underlying smooth component. I mean, Westfold and I argued about number densities that were required to hide sources, you see. I remember one day we eventually got down to saying "Well, it's got to be individual electrons, essentially".

Sullivan

Well, but hold it now, in one of your papers with Westfold you have a model in which almost all of the radio sources are closer than 40 parsecs and you give an actual density of these radio stars- I believe that's correct. In ‘51, in one paper of that series, you talk about an isotropic component which might be extragalactic and a galactic distribution of radio stars less than 1/10,000 per parsec. The average observed radio source is much more luminous than the Sun and at distances of less than 40 parsecs.

Interruption

So this was 1951, now, so it was probably written around 1950, so at that stage you still, apparently, were thinking of the radio star idea. Can you remember when this?

Bolton

Yes, I think the changeover probably came in 1951 to 1952. And I felt that there was a smooth radiation from our Galaxy and that the majority of the discrete sources were extragalactic, and had to be galaxies. In other words to give them a moderate volume emissivity. Of course, the pulsars have proved the exception.

Sullivan

That's really irrelevant to the 1950's.

Bolton

No, I think if you can ever get hold of the proposal I wrote to Caltech by 1955, although I'd been out of the subject for a long time, that proposal came remarkably true. The thing that was obvious then, I think, was that we did have galactic sources and we did have extragalactic sources. But one of the distinguishing characteristics was that the galactic sources had the same dimensions optically as radio. The extragalactic sources had much larger dimensions in the radio, and one of the ways of getting at the identification was to look at the structure and say, "Well, we’ve got a four minute of arc source, this is either a four minute of arc galactic nebula or it's a half-minute of arc galaxy".

Sullivan

And for some reason the radio emission is outside.

Bolton

And for some reason the radio emission is outside.

Sullivan

But I'm trying to think now, what else was there besides Cygnus, in terms of a large radio galaxy?

Bolton

Ah, well, I mean Bernie [Bernard Y.] Mills' work, our crossed sea interferometer, the Formax source, Centaurus...

Sullivan

Centaurus, right. There still was only a handful, but there was a definite pattern.

Bolton

Yes, still only a handful. The known supernova remnants, the Crab and the Puppis source and so on, were the same size optically. That is to say, the radio description was the optical description.

Sullivan

But might there have been a bit of a selection effect there, because the upper limits to sizes that one give at that time were something on the order of a minute of arc? Well, there might have been some galaxies that were bigger than that. What I'm saying is that it might not have been possible to establish at that date that a radio source was smaller than the optical image it's associated with. All you could find was that it was larger.

Bolton

Oh yea. I mean there was a great spate of interferometry around 1952- [Robert] Hanbury Brown’s, Bernard Mills’ work.

Sullivan

Right, but only on a couple of the stronger sources, that was all you could do it on...

Bolton

I think they gave a very clear indication that structurally the galactic sources were similar in radio as they were optically, and the extragalactic sources were very much more extended.

Sullivan

Okay.

Bolton

Not true, of course, for things like quasars.

Sullivan

Yes, which is once again, a later story. Let's talk about the Bolton and Westfold papers in which you switched from the discrete sources to the galactic background at 100 megahertz, but from what we've been saying, this really wasn't a switch in your mind at this time, it was just a different aspect of the same problem, I guess.

Bolton

Yes. We built for the first time a steerable antenna.

Sullivan

Right, and didn’t use the sea interferometer technique.

Bolton

Well, we used the same, actually the 9-Yagi steerable antenna was on an equatorial mount, but it had a third axis in it, which when you pointed it to the sea, you could rotate. The declination axis became the horizontal axis.

Sullivan

Oh, I see.

Bolton

Yes, it had a broken declination shaft in it with a rotation.

Sullivan

But what I'm getting at is from an astronomical point of view, in your mind at that time, you would consider this just a different aspect of the same problem as the discrete sources?

Bolton

Well, we had some radiation and it was our job to study it.

Sullivan

Right. And what do you think were the primary results that came out of that 100 megahertz survey?

Bolton

The galactic radiation one?

Sullivan

Yes.

Bolton

Well, as our antenna was too small...

Sullivan

The resolution you had, I think, was 17°. Nevertheless, I think it did give you hints.

Bolton

There were technical problems, like establishing the antenna temperature scale, matching receivers to antennas and that kind of thing. That was one of the first large antennas on which spherical integration was used to determine the gains of it.

Sullivan

Spherical integration, I'm sorry, I don't know what that means.

Bolton

Spherical integration of the beam pattern.

Sullivan

By using a transmitter or something?

Bolton

Yes.

Sullivan

And actually, since you bring it up, was that transmitter far enough away as it turned out?

Bolton

It was the Sun.

Sullivan

Oh, you used the Sun. Someone else used a transmitter a mile or so away and it turned out there was a calibration error

Bolton

That was Christensen.

Sullivan

They didn't realize how far the far field was, I think. Okay, you clearly realized you didn't have enough resolution, but nevertheless, you seem to have plunged into quite a bit of analysis of this survey with Westfold, I assume, sort of churning away on models and this sort of thing. In fact, you even went so far as to jump into the argument of trailing arms versus leading arms. What was that based on?

Bolton

Well it was based on the angle of the concentration in Cygnus.

Sullivan

On the two dimensional sky, I'm just not quite sure how you can see whether it's trailing or leading?

Bolton

I can't answer that question myself.

Sullivan

I'm afraid I haven't looked at the paper, only the abstract. You can see a concentration for an arm...

Bolton

Well, it was based on the angle- we knew which way the galaxy was going around. I forget what it was based on, that, but it led to quite some arguments for a few years.

Sullivan

Yes. And what about these secondary peaks that, of course, had shown up in earlier surveys by [Grote] Reber and so forth? You had the one in Cygnus, then you have Sagittarius- was it beginning to become clear from this survey that Sagittarius might be more than just a diffuse concentration?

Bolton

No, our work on Sagittarius really didn't get going until we got the 80 foot hole in the ground.

Sullivan

Okay, so, at this stage then you weren't really thinking of it as a discrete source in any sense?

Bolton

No, although [John "Jack" Hobart] Piddington had found it as a discrete concentration at, I think, 25 cm. And then [Richard X.] McGee and I with the 80 foot dish really mapped that region. I mean, building the 80 foot hole in the ground was partly dominated by the fact that we could see the Centaurus source, and we could see the region of the center of the galaxy.

Sullivan

So what you're saying is this was another strong point for such an antenna that these things went near the zenith and...

Bolton

Yes. Well, we did have the choice of building it off axis. We could have built it on a slope.

Sullivan

Well, that's true.

Bolton

In fact, it was very difficult to build it straight up.

Sullivan

Why’s that?

Bolton

With the configuration of the land, there was an awful lot of sand to move.

Sullivan

I see. But once again, that's getting a little bit ahead. Another interesting thing is that in the 1950 paper on the 100 megahertz survey you use a type of restoration of the beam. Where did the idea for this come about?

Bolton

I can't really remember. I suppose I must have suggested it to Kevin and we simply got going on it. It’s a very similar in fact nowadays to the "Clean" Program.

Sullivan

Well, is it really?

Bolton

Yes, the integration process which we used is not allowed to produce any holes.

Sullivan

Okay. You were not bothered at all by, I don't imagine at this stage you were thinking in terms of Fourier theory, which [Ronald N.] Bracewell brought in a few years later?

Bolton

Well, in fact, we did Fourier transform.

Sullivan

So I see, in the mathematical analysis of this restoration. But you had no philosophical...

Sullivan

Continuing with John Bolton on 15 March ’78. You had no reservations about maybe getting more than was actually there?

Bolton

No, in fact, we weren't getting more than was actually there. We knew it had to be, we didn't push it very far. I mean we knocked it down from what was something like 17° beam to a 12° beam.

Sullivan

Oh, is that all? I see.

Bolton

Yes, we used the, we had additional data. We had the same kind of map rising above the sea, essentially half the antenna. We knew what was in discrete sources and so on. We didn't attempt to...

Sullivan

You didn't really sharpen it up all that much?

Bolton

We didn't really sharpen it up all that much, no.

Sullivan

Okay. Once again, I have not looked at the paper itself recently, so I was only looking at the abstract.

Bolton

I think we split our beam into something like twelve pieces- a center, a surrounding circle and then maybe four quadrants surrounding that, with equal loading in the antenna pattern.

Sullivan

I see. We need to talk about the 80 foot, the building of the 80 foot. Dick McGee has told me about how you like to get out with a shovel and have your workers out there with a shovel. It seems to be the Bolton style. Can you tell me about the actual construction of the thing? Were there any particular problems?

Bolton

I think, it was really Westfold and I who started the big dig.

Sullivan

But even though he was primarily a theorist in orientation, he was out there digging?

Bolton

Yes, sure. Westfold and I started it by ourselves and Bruce Slee decided that it was going to be a good thing and later on Gordon Stanley joined in.

Sullivan

And also Dick McGee, or did he come on later?

Bolton

No, no. Dick didn't join in until the 80 foot was finished. Originally we had 160 megahertz, this was just hollowed, this was just formed from sand but around the edge we did build up some timber to extend it a bit. We initially coated it with the strip metal that you bind packing cases with. We just laid out strips.

Sullivan

I see. It wasn't a mesh then?

Bolton

No, it wasn't a mesh at that stage. We clipped the intersection and of course, that worked quite well for 160, but once we pushed it to 400 we had to put some concrete on to maintain the surface from drifting. And then we built the proper edge, I think the last four feet were just steel tubes, bent steel tubes stuck into the concrete and then wired around it and then chicken wire mesh covering the whole thing.

Sullivan

I see. Where was the location of this relative to the main blockhouse, which I’ve seen?

Bolton

Probably about 80 yards north and slightly inland of the main blockhouse.

Sullivan

But pretty much on the cliff?

Bolton

Yes. It was very close to the cliff edge.

Sullivan

And do I have it right that you actually were just using shovels to dig this thing out?

Bolton

Yes.

Sullivan

No equipment of any sort?

Bolton

No.

Sullivan

Was this...

Bolton

In fact if Pawsey had seen it, it would have been banned.

Sullivan

If you had equipment?

Bolton

No, I mean if Pawsey had seen the dish, it would...

Sullivan

You mean this was all done on the sly?

Bolton

Yes. It was done on the sly. Bowen knew it was going on, he came out and saw it one day and rubbed his hands together greatly and...

Sullivan

Why would Pawsey have objected?

Bolton

Well, it was obvious that it could be used at wavelengths which weren't in our allocated zone. You see, Radiophysics was broken up, we weren't allowed- one of the things that annoyed Westfold and I very greatly was that we weren't allowed to look for the hydrogen line very early in the piece because Westfold had translated [Iosef Samuelovich] Shklovsky's paper. We couldn't actually, we could never get across to Joe that this was atoms emitting a line frequency.

Sullivan

And what was, were you interested from the point of view of being able to get Doppler shifts, what was your real, or was it just something to do?

Bolton

Well, we wanted to see if we could detect it.

Sullivan

Just to do it.

Bolton

Yes, just to do it.

Sullivan

When was this now that you're talking about?

Bolton

Oh this must have been 1949.

Sullivan

Did you know about the Dutch?

Bolton

No, I didn't find out about the Dutch effort until I went to Europe in 1950, this was pre-1950, and I think we were told that 200 megahertz was our limit. We actually used the 80 foot dish to try to detect the deuterium line.

Sullivan

That's right. That came along a bit later. We'll come to that. This is interesting though that you had a definite strong interest in the hydrogen line at that early date. Pawsey, however, did not, then?

Bolton

I think he didn't understand, see. Pawsey was, although he did train us as physicists, got into ionospheric work and radio, he didn't understand that atoms would emit radio frequencies.

Sullivan

You think so?

Bolton

Yes. He's quite, this was quite outside of his comprehension at that stage.

Sullivan

Once again, I had almost testimonials from many people about his marvelous physical insight. What you're saying is that this had definite bounds to it. But it is true though, it wasn't just a matter of keeping you out of it.

Bolton

He must have, he knew enough physics, he knew what the Bohr atom looked like and so on, the extension to transition...

Sullivan

Hyperfine transition.

Bolton

Hyperfine transition was really subsequent to his physics.

Sullivan

But what I'm saying is that it wasn't just a matter of keeping you out of it, he didn't have any of the high frequency people try to look for it either, until they got the word from [Edward Mills] Purcell.

Bolton

Yes. And of course, I was in Holland in 1950, you see.

Sullivan

Even after you came back.

Bolton

I spent some time at Leiden and I sent descriptions about what the Dutch were doing and everything like that. And I sent descriptions from Harvard of what [Harold Irving "Doc"] Ewen was doing.

Sullivan

Well, [Frank J.] Kerr was doing that also. Kerr was also doing that from Harvard.

Bolton

That's right. Kerr was at Harvard when I went to Harvard.

Sullivan

That's right.

Bolton

And Kerr was doing it, so there was no, Pawsey just, I mean, he had a complete mental blockage.

Sullivan

Okay. Well, we've gotten this straight here. You were saying that Pawsey would not have liked the dish because it was designed for higher frequencies and it does seem to me from talking to everyone that there were very small groups with neat divisions as to their sphere of operation. But you've been in a lot of management, do you not think this is a reasonable way when you've got an awful lot of clever people you've got to keep them somewhat from running all over each other.

Bolton

It was a very good way in those early days, yes. I mean, I think, a lot of good people came together then. The outstanding people, one of the most outstanding people was Ruby Payne-Scott, and unfortunately, women in the public service had- well, she was discriminated against for basic reasons of sex and other reasons- she was a very aggressive person indeed. There was Paul Wild, Bernard Mills...

Sullivan

[Wilbur Norman "Chris"] Christiansen?

Bolton

Christiansen was sort of a later era. And with simple pieces of equipment you can make rapid progress, and we used to hold meetings in which, maybe every two weeks or a month, somebody would always come up with something very, very interesting.

Sullivan

This is a meeting of all the scientific staff?

Bolton

Yes. We had a thing called Radio Research Board, they were the actual people doing things were very [???] bodies in this meeting. But they were the important people.

Sullivan

Now this radio research board, this is the Australian organization, isn't it?

Bolton

Yes.

Sullivan

And they used to meet at Radiophysics.

Bolton

Yes, that's right. It was dominated by ionospheric physicists and so on. But it wasn't the way to go on, it was all right for the initial discoveries which could be done with not much money and so on. But Australia lost out very badly in the 1950's because of this.

Sullivan

This same style kept on going?

Bolton

This same style kept on going. And I remember in 1950 going to NRL [Naval Research Laboratory] and seeing that 50 foot dish being put together and thinking, "Hell, unless we did something like that, they're going to drown us as well." Of course the history of NRL is such that they didn't. But they could have done it- working in centimeter and millimeter ranges and so on.

Sullivan

Well, of course, that was an entirely different environment for working in. I don't see how they could have drowned you.

Bolton

Well, they only had to start a sky survey- to drown us. I mean the potential positional accuracy.

Sullivan

Well, their thing had real pointing problems, though, too, you know. It was an old gun mount, it had a good surface, but...

Bolton

Yes. It had the wrong people. It wasn’t until [Edward F.] McClain came up- there was an engineer.

Sullivan

I see what you're saying. But in any case, what you're saying is that the style was not appropriate to the way the science had changed. And you think this transition took place around 1950 or 1951?

Bolton

Yes.

Sullivan

And now once again, we've strayed from talking about building your hole in the ground. So this was the reasons that you didn’t get any simple earth-moving equipment?

Bolton

We didn't have any money. I think the aluminum mask, the 40 foot of new aluminum tubing exhausted our funds for the year, you see. Everything was built from scrap.

Sullivan

Another thing that puzzles me is how you could really do this without Pawsey knowing, because apparently he lived near there and used to stop by...

Bolton

It was behind the...

Sullivan

Was that the reason for the site selection?

Bolton

Right. There was some high scrub growing around it.

Sullivan

Okay. Having gotten this dish, what did you do with it?

Bolton

We did a survey at 160 megahertz, which didn't, in fact, do very much. I think the beam of 400 was about 1°, so at 160 it would be 3.5 or something like that. And this just said, "Well I'll work at 100 megahertz." We haven't gone wrong; we haven't pushed our deconvolution as far as we could have; we haven't overdone it. But 160 was really just, I think we did produce the contours at 160 and at this stage, we convinced Pawsey that it would be worthwhile if we could get the sensitivity of making the dish surface sufficient to work at say, 400. At that stage we got the okay to go ahead at 400. We got the money for a few cubic yards of concrete and chicken wire.

Sullivan

I'm a little confused here now. Bolton, Stanley and Slee survey is 100 megahertz that was published in 1954 was based on the old Yagi?

Bolton

This was the twelve Yagi mount.

Sullivan

Right.

Bolton

Just azimuth only.

Sullivan

So that was before the hole in the ground?

Bolton

No it wasn't before the hole...

Sullivan

Sort of simultaneously?

Bolton

It was contemporary with the hole in the ground.

Sullivan

I see.

Bolton

We dismantled the, Stanley had managed to get a 15 foot dish built and we put the 15 foot dish on the old 9-Yagi mount.

Sullivan

I've seen those pictures.

Bolton

We used the structure which held the Yagis, modified it to give us an azimuth resolution, and the 15 foot dish we used at, we used that so we could vary our frequency a little. But it was never used for scientific work really. It was just used to test out equipment and so on.

Sullivan

So you had both of these things going at once?

Bolton

Yes, oh yes.

Sullivan

And...

Bolton

Well, both were an attempt. You see, we had effective resolution in zenith angle with a sea-interferometer and the fact that we had a sharp horizon. So we spaced the Yagis fairly far apart to give us a good beam there.

Sullivan

In the vertical direction?

Bolton

Split beam- a split beam but we weren't interested in this section. We put the 6 Yagis horizontally to give us quite a lot of azimuth discrimination. And this is what scaled up the 20 source survey there to the 100 source survey there. But of course, sea-interferometer observations were very laborious. You didn't do a survey. I mean even though you might only want ten positions around the sky [Sullivan: horizon] to do the survey, ionospheric effects and so on, there were nights when you got nothing. I mean there was only one night a week that you got good observations.

Sullivan

Did you always want to have two independent observations? Of any given strip of sky?

Bolton

Oh, yes. Many.

Sullivan

And what was the result of that? Did you find that, in fact, this was a good idea or that things weren't quite reliable? I mean if you took just a single strip of sky that you could get pretty reliable thing from one...

Bolton

Oh, well, I mean as I say, we'd leave it in one azimuth for a week or two weeks.

Sullivan

Oh really? I didn't realize that.

Bolton

And then, of course, we couldn't work- thunderstorms out to sea were one problem, so that even though we might leave it in one azimuth for a week we'd only get coverage of about eight hours of right ascension. The rest would be chopped up by the ionosphere or thunderstorms. So we'd have to come back three months later and do it again to complete the sky coverage. So the 1954 paper was actually something like two years of observations.

Sullivan

I see. That explains why it was a bit later. Was this such that it had to be tended all the time or could you leave it overnight on automatic?

Bolton

We did develop, well one of the problems the galactic plane rises and so on and you have to be there to turn the strip chart down. But Stanley and I did build [Miller integrated?] circuits with time constants of an hour or more in which we smoothed out everything...

Sullivan

I see.

Bolton

And did a delayed subtraction which meant that instead of having to be there for eight hours of the night, while the Galaxy came in and went out, it was maybe only the sharpest part of the galactic plane coming in. So we used that...

Sullivan

As a filter against the...

Bolton

I think that's described in the paper.

Sullivan

But once again, we've drifted off from the 80 foot. I was just trying to find the publication of the 160 megahertz 80 foot [Sullivan: 72 foot].

Bolton

That was never published. [Sullivan: But it was- Wayne Orchiston!] [Australian Journal of Physics vol 7 page 96 from 1954. see fig 1 page 98]

Sullivan

Okay. That's why I can't find it. Because it really didn't tell you anything differently?

Bolton

No. It convinced Pawsey that we should go on and work at a higher frequency.

Sullivan

And that the dish worked.

Bolton

Yes. And, of course, McGee joined us about that period. He and I became convinced that indeed we were seeing the center of the Galaxy in the Sagittarius source.

Sullivan

Once you were at 400?

Bolton

At 400.

Sullivan

Right.

Bolton

At 100 megahertz- essentially in self-absorption. So you don't see it with, well, I think, at 80 megahertz, it’s in prominent self-absorption. I believe Bernie Mills showed that with the first cross.

Sullivan

And at 400 you would have a beam of, you said, 1° or something like that. And so that was getting down to...

Bolton

Was it a 1°? No it wasn't 1°.

Sullivan

Let's see. An 85 foot at 1400 used 40 arc minutes, so it would be...

Bolton

More like 2°. So 160 was about 6° or so.

Sullivan

But once you found that you were getting a sharp peak with a 2° beam, you were willing to call it a discrete source and I guess bolstered by the fact that the galactic coordinates went right at the...

Bolton

[???] 30° off.

Sullivan

Well, yes. But they agreed with other determinations of the center- optical ones. Or is that correct? I assumed by that time optical people also were saying that the center was 30° away from the...

Bolton

Yes. I think we had done our 100 megahertz survey which certainly pointed to the galactic center being there. And the plane is very different. One of the things the 100 megahertz survey said the galactic plane is in the wrong place.

Sullivan

How far different?

Bolton

Oh, about 1.5°. This was one thing which Oort was very enthusiastic about because when I went to Leiden in 1950, Van Taulder had just made a new determination of the galactic pole, I think, based on the motions of interplanetary nebulae.

Sullivan

What was his name?

Bolton

Van Taulder. And Van Taulder's pole agreed very nicely with our plane.

Sullivan

And not with the classical Olsen pole?

Bolton

Yes, that's right.

Sullivan

That's interesting. Even with a 17° beam you could get it down that fine, because of course, it's actually it's just one parameter for the entire survey. So that this all made sense and what is your opinion as to who should get the credit for the recognition of Sagittarius A or is your opinion that it's really a semantic thing as to when a source becomes a source- it was just a continual process?

Bolton

Well, I think Piddington was the first person, Piddington named Sagittarius A [Miller Goss: Not correct, W M Goss 18 June 2004. See Palmer and Goss, "Nomenclature of the Galactic Center Radio Sources" Galactic Center Newsletter (1996), vol. 2, p. 2]. Now at that stage, its position was not accurately known, it was terribly vague. It was an object which we couldn't find with sea-interferometer or anything else we did at 100 megahertz. It was an object which we found and defined rather precisely it's position at 400, and it really stood out there. And it stood out as a center of the contours around it. I think this was an important thing. It agreed with the location of our 100 megahertz- I think McGee and I put all these arguments together in the paper which said we are convinced we are looking at the galactic center. Now this wasn't accepted for quite a long time.

Sullivan

Oh yes, and of course, back to NRL they argued that it was only a couple of kiloparsecs away when they had some hydrogen absorption information. What other arguments were there that people did not like this to be the center of the Galaxy?

Bolton

I think the sort of optical backlash from many astronomers. "You can't just come along with a radio receiver and do what we failed to do in the last hundred years."

Sullivan

In terms of determining a good galactic system of orientation and so forth?

Bolton

Yes. But Oort was certainly one person who supported this.

Sullivan

What about someone like Baade, who was quite concerned with galactic structure also?

Bolton

I think Baade was a little bit jealous, because he'd been trying to find the galactic center by finding holes in which you could look at the increase and then the decrease in the star density.

Sullivan

Okay. The 80 foot- what other projects did it work on?

Bolton

Well, actually, of course, I got out of it at that stage.

Sullivan

Oh yes. Well, tell me about that. I don't have that.

Bolton

I went into rain physics then.

Sullivan

Right, but how did that come about?

Bolton

It came about because I lost out essentially. Bernie Mills had built the small Mills Cross, the experimental one. What I wanted to do, one of the things that we'd shown was this little 15 foot dish which Stanley had built, even though we had very poor signals, was that we had worked sea-interferometry right up to 400 megahertz on the strongest sources we could see. And shown that all the ionospheric nasties disappeared as one went to higher frequencies. So our proposal was that we should build a much more elaborate sea-interferometer. And it was going to take the form of, well, almost an Ohio, it was going to be 200 feet in...

Sullivan

You mean like [John D.] Kraus’ antenna?

Bolton

Yes. Like Kraus’. 200 feet in aperture, 20 feet high, and was going to be made of- there are lots of tennis courts around Sydney in those days, thousands of tennis courts, and it was simply going to be made of the standard tennis court construction.

Sullivan

I see, a real Australian...

Bolton

With 20 foot high poles and wires, a sort of wire mesh that was put on tennis courts. A stacked vertical feed for it, which would give it, I think it was a 4° beam over the horizon. It was going to be 400 megahertz. But an azimuth beam which was only a degree.

Sullivan

But how was it steered in azimuth

Bolton

It was steered in azimuth by moving the stacked feed. It was a [???] ratio.

Sullivan

Oh, I see.

Bolton

And it would cover, the same type of ratio as the actual dish, or a bit longer, and one could cover something like 20°. The stacked feed was going to capable of moving. And when you've done that 20°, you took the whole thing down and put it up pointing a different direction.

Sullivan

I see. And about when did you propose this?

Bolton

This must have been proposed at the end of 1952.

Sullivan

You wouldn't happen to have a copy of that proposal?

Bolton

Oh, no. That was no proposal, it was just...

Sullivan

You mean it was never written down?

Bolton

Oh, no. Just in talking to Joe and Taffy. We had lots of proposals, but one of the alternate proposals which Taffy was very keen on, was two rolling barrels with line feeds which would also work at 400, that is to say, combined the sort of 80 foot dish but as a rolling barrel. In fact, it was Taffy’s idea, the rolling barrel. And we'd make two rolling barrels which would give us 2° primary vision with the interference pattern for resolution.

Sullivan

This proposed sea-interferometer, was this going to be at 400 megahertz?

Bolton

That was 400.

Sullivan

It couldn't be much less with tennis court sort of wire. It couldn't be much higher frequency. The reason for doing that, I guess, was to keep the cost down. Would you have liked to go on to a higher frequency?

Bolton

No.

Sullivan

Why not?

Bolton

Because we knew the sources went down with frequency, so this was a kind of compromise.

Sullivan

However, Radiophysics could only support one of these largish projects, I guess, and who made the basic decision?

Bolton

Pawsey.

Sullivan

Well, that's sort of interesting, because I thought Bowen was the boss.

Bolton

Yes, but Pawsey was really in charge of the group.

Sullivan

Right, but for instance only a few years later, Pawsey lost out on...

Bolton

That's right, Pawsey lost out. Bowen took it on to his own. Bowen wanted this thing.

Sullivan

The Parkes dish.

Bolton

Yes. And he wasn't prepared to fight Pawsey over- he was prepared to fight Pawsey over this, but not over something which was not an integrated effort in the division, while we were all sort of in little sub-groups. So, actually, Stanley and I had done an awful lot of work and we proved that essentially this kind of thing to our own satisfaction would work. This was the way to go about it. At 400 we had no trouble in the ionospheric low angles, we got interference patterns on Cygnus and Crab, which were terribly consistent from day-to-day and minute-to-minute. And we felt with a 1° by 4° plus the sea-interferometer within the 4°, I mean, it's 1° in azimuth but an object seen from the horizon and then disappears out of the 1°, so you've really got much more, you've probably got the equivalent of about 1° antenna plus the sub-structure of the interference pattern. We felt we could detect several hundred objects and get accurate positions. As I say, we lost out to Mills.

Sullivan

But this must have been a difficult decision because here you had two good ideas going to do similar things. Was it really a matter that Pawsey said one is bad and the other is good? Somebody had to win it and somebody had to lose?

Bolton

Well, in a way, ours was the brute force method whereas the Cross was an esoteric. The Cross was using electrical engineering, we were using brute force.

Sullivan

So the Cavendish tradition...

Bolton

The Cavendish tradition won out. And well that’s too bad, at that stage, we lost a couple of our rain physics in an air crash and Taffy said, "Would you think of flying again?"

Sullivan

And so although you had not worked in rain physics at all, you...

Bolton

No, but I had done a lot of it. I had done a lot of flying. And I knew what one saw, I mean, I'd worked on, I'd had an interest in radar, ship radars at sea, and atmospheric effects.

Sullivan

This still seems somehow surprising to me. You were obviously a pretty well-known radio astronomer at this time and yet you were willing to just drop that subject. Or were you always thinking of this as a temporary thing?

Bolton

No, I didn't think it was a temporary thing. Well, I mean, Taffy said that, "If we ever get the dish, it's yours and so on," but I'd come to the end of what I could do with little bits and pieces.

Sullivan

You just came up against a wall, more or less.

Bolton

I'd come up against a wall, I'd have a proposal in to extend it, to break the wall down and it hadn't worked out.

Sullivan

Of course, the other option would be to go somewhere which you eventually did, to go somewhere else. The sea cliff interferometer at this stage, it would seem to me, was becoming a little bit unworkable or maybe you wouldn't agree with that.

Bolton

I think this 400 proposal would have worked.

Sullivan

But the advantages of it are, well, what do I want to say- did you feel by this time that you understood the refraction problems and so forth?

Bolton

Oh, we knew at 400 that we didn't get the irregular refractions that we got at the lower frequencies, I mean the straight refraction with optical.

Sullivan

And the ionosphere was much less of a problem.

Bolton

Yes, we were dealing with, there was no doubt with that instrument we'd have got positions to 1 minute of arc without any trouble whatsoever.

Sullivan

So would you say it's not fair to say that the cliff interferometer faded from the scene in the early 1950's because it had nothing more that it could do? It was really more because of this decision?

Bolton

It was because of this decision, yes. We could have extended it; it essentially would have done what we did later at Caltech, ten years later at Caltech.

Sullivan

In terms of minutes of arc positions on several hundred sources?

Bolton

Yes.

Sullivan

I'm trying to get at a comparison between the Michelson interferometer, which was being heavily developed at Cambridge, and the sea-cliff interferometer which was the first technique down here. Frankly, I've always thought in my mind of the sea cliff interferometer as a great idea, but all of a sudden it loses a lot of flexibility and you always have to work near the horizon and you can't change your spacing.

Bolton

Well the sea cliff interferometer enabled us to do a couple of Yagis what it took very larger aerials to do at Cambridge.

Sullivan

I don't quite follow that. The sensitivity, you're doubling your collecting area.

Bolton

4x.

Sullivan

4x. I'm sorry, I'm not aware of that. How does that come about?

Bolton

It has 4x the collecting area because the signals are added together in space, so you don't have the impedance problem.

Sullivan

That's right. Not on the line, yes. Well, still, you didn't have that big an array - they had 4x that, it's not...

Bolton

No, we didn't have that big an array, but if we had put what we were proposing...

Sullivan

Oh, yes. Now there, yes, then 4x became a huge thing.

Bolton

Became a huge thing. It was essentially a 100 x 200 foot dish, was what we were proposing to build.

Sullivan

So you could never have gotten that amount of collecting, equivalent amount of collecting equipment at that frequency?

Bolton

At that price.

Sullivan

At that price, yes. That's an interesting point. So if this thing, in fact, had been funded, it might have gone on for three or four years making such a survey.

Bolton

Well, but funding was a few hundred dollars as against $30,000 which the Cross took.

Sullivan

Really?

Bolton

Oh, yes.

Sullivan

Is that all it was going to be?

Bolton

Yes. It wanted 22 inch 20 foot poles.

Sullivan

Well, then I'm confused as to why there had to be a decision between the two. I thought it was a matter of, from a financial point of view.

Bolton

No. We had a factor of 10 on our side in doing it.

Sullivan

Then why did there have to be one or the other? Or was that not necessarily true, it's just a matter that Pawsey said, "I don't like this idea and it's not because of the Mills Cross that you can't do it, I just don't like the idea?"

Bolton

Well, part of this was the Radiophysics system of accounting, which only accounts for material you have to buy. The material for the Mills Cross was only a factor 2 or 3 higher than the material for ours, but the labor costs and workshop were not counted.

Sullivan

I see.

Bolton

That's one thing which I've always objected to; one should properly account for things. That's one reason why people like Christiansen and Mills got in terrible strife when they moved away from Radiophysics and tried the same scheme of accounting. They had to find the real costs, not the apparent costs.

Sullivan

Okay. Let's see, the 80 foot did some other things besides this survey at 400 megahertz, and once again, I'm trying to find the publication for that. When was that?

Bolton

Well, it wasn't published until after the Russians, it wasn't published I didn't think until 1956. This was Stanley and Price.

Sullivan

I see. You're not on it.

Bolton

No. In fact, I didn't take part in the experiment at all. I was in rain physics by this time.

Sullivan

Oh you're talking about the deuterium.

Bolton

Yes.

Sullivan

But I was thinking about the survey of radio sources or was there never actually a survey undertaken?

Bolton

No. The 80 foot dish was, I think McGee and I published the contours and the Sagittarius source and that's essentially the only publication that came out of it. You see, the group broke up at about that stage.

Sullivan

Because of your leaving?

Bolton

Yes. Slee went, I think, to Mills. I went into rain physics. McGee and Stanley continued. Westfold had gone to Sydney University to full-time teaching. McGee and Stanley and Paul Price, who came out a as Fulbright Fellow, did the deuterium.

Sullivan

Right. Tried to check up on the Russians who claimed detection.

Bolton

No. It was the first experiment.

Sullivan

Is that right?

Bolton

This was 1953.

Sullivan

The Russians were 1955, I guess, the Jodrell Bank Symposium.

Bolton

And we got our old records together and we didn't publish the negatives you see, which I think was ten times below the Russian positive plane.

Sullivan

I didn't realize that. And was that ever published? After the Russian claim?

Bolton

Yes.

Sullivan

Just taking the old data?

Bolton

Yes. In Nature in 1956, I think.

Sullivan

I see.

Bolton

But it was published from Caltech, not from Radiophysics, you see. Published from Caltech and MIT.

Sullivan

So you worked in rain physics for two years or three, was it?

Bolton

Around three, I think.

Sullivan

And just to complete the story, I should ask you just very briefly to describe what were the problems that you were working on?

Bolton

I looked into, Taffy was keen that actual experiments to modify weather should be carried out. I really had a free hand. I did a lot of work on the design of burners to work safely in aeroplanes. In fact, the first thing that greeted me when I came back from Caltech in the beginning of 1961 was somebody who was trying out a new burner and said to me, "Well, this is the model that supersedes yours," which was eight years earlier and its ten times more efficient and solid, "You should have been something eight years." I worked on determining the critical temperatures of- I essentially worked myself through inorganic chemistry and vaporizing, producing aerosols from chemical substances I could find, and finding out what temperature then produced [?] nuclei. I built equipment for monitoring the upper atmosphere, for trying to pick up meteor dust in high flying aeroplanes. This was a long [?], an accelerator which particles impinged on moving film of a substance which shall remained sticky at -40° centigrade.

Sullivan

So this was not really Radiophysics then.

Bolton

No, I worked on- I tried out ground based generators for rainfall stimulation in the Victorian Alps and [?] hydroelectric scheme. I also did some work on how difficult or how easy it was to prove that you'd done something if you did make rain and so on.

Sullivan

From a statistical point of view?

Bolton

From a statistical point of view. Try and find two areas in which you can actually measure what you've done, either in snowfall or river runoff or that kind of thing. And all the problems of going through it like different evaporation rates, different seepage rates and that kind of thing.

Sullivan

Yes. That must be a terribly difficult process.

Bolton

People have done these things, you see, without ever looking at...

Sullivan

If it rains two days later, you caused rain, yes. But then you came back into radio astronomy, and how did that come about?

Bolton

This was mainly through Taffy again. It was sort of an old boy network from the radar people during the war and the Office of Naval Research had tried to get Caltech interested in radio astronomy and Lee DuBridge was then president of Caltech wrote to Taffy, who was one of his war-time colleagues, to suggest a person who should come to Caltech to start it. Taffy produced my name and this of course was supported by Minkowski and Barlow from our old association. So I went to Caltech.

Sullivan

What was the attraction of it to you?

Bolton

Essentially, that I could take off, continue where I'd left off in the problem of radio identification. The intervening years essentially hadn't produced anything, and of course, I did start again where I'd left off- at the high frequencies...

Sullivan

Had the decision been made for the two large dishes?

Bolton

No. As a matter of fact, Caltech was sort of thinking in terms of a Mills Cross and Stanley and I went into the Mills Cross and we realized its very great difficulties. The fact that it was voltage product thing and side lobes would be one hell of a trouble, particularly with standing waves along the long line and that kind of thing, which later turned out to be correct.

Sullivan

In terms of producing bogus extended sources? Well, not necessarily extended.

Bolton

It gives you a confusion background. And so we proposed the two 90 foot dishes working, well we had decided to work at 400. Stanley had finally got hold of a Western Electric 437, 436 combination, which enabled you to get really good noise figures at 400, down below the 3 dB level. He continued to work in that field and built switches. So we believed we could make very sensitive radiologist at 400 megahertz.

Sullivan

Let me just go back to, you say that ONR [Office of Naval Research] actually approached Caltech instead of vice versa?

Bolton

Well, this is the story I'm told. In fact, I was always told at Caltech when I got pretty shirty about why I couldn't have some staff which the University would pay for, and they said, "Well, you know, we were talked into this - it wasn't our idea."

Sullivan

John Bolton on 15 March ’78. You said that someone at ONR had always wanted to put a radio dish up on Palomar?

Bolton

No. When I said put alongside, I meant figuratively.

Sullivan

I see. So you went to Caltech in 1955 and brought Gordon Stanley with you. And what was the situation you found there? Did you have a lump of money and had to decide...

Bolton

No, I didn't have any money. I found I had a grant of $90,000 for the first year from ONR, and there was no university support yet with it. In fact, the university was taking 33% of that in overhead. And I essentially had to think of what I was going to do. I had talked in letters to Dubridge about the possibility of using an interferometer, a variable spacing interferometer, consisting of two quite sizable steerable telescopes or perhaps a Mills Cross. At that time I hadn't made up my mind, it was only when Gordon and I started looking at the Mills Cross and all of its problems that we decided the dishes were the thing and the high frequencies. And then I had to write a proposal to try and get money. We tried approaching the Rockefeller Foundation for money and that approach was actually in competition with Taffy Bowen’s approach on the 210. But ONR were really staggered when I came up with my first estimate of what the Owens Valley was going to cost - something of the order of $760,000 was my first accounting for this, you see. But they really did back me very handsomely as it turned out, it was closer to a million four years later and three quarters of a million was estimated, it wasn't too bad.

Sullivan

But in fact, your proposal was for two 90 foot dishes?

Bolton

Yes.

Sullivan

It didn't have to get scaled down?

Bolton

No. 90 foot was a sort of larger size. I could see Dover Heights, I could look at my 80 foot hole in the ground and visualize that on a mounting, but then I looked 220 feet down to the sea and I couldn't see that on a mounting at that stage. At least not as far as I was concerned.

Sullivan

That was a whole new regime.

Bolton

That was a whole new regime.

Sullivan

Which, of course, was the Parkes dish and the Jodrell Bank dish demonstrated. But how long did it take to get this money, first of all? And then tell me about the construction and so forth.

Bolton

Well we just continued on around $100,000 budget a year. We had a small group, [Thomas A.] Matthews joined us. We built- first of all, we had to do a site survey and find out where the best place would be - this took maybe six months. In the meantime, Stanley was keen to get a small dish built - a) to experiment with the receivers, b) with the drives. So in the first year, we started working on the 32 foot dish, which we build at Palomar, which was a model of, I remember building out of different pieces of brass wire and so on. What I felt the restricted polar axis design with intersecting axes was the cheapest of all. It wouldn't give us, get us ±4 hours an hour angle, that was a restriction on it. And of course, Bruce Rule and C. W. Jones started pushing backwards and forwards the ideas on the actual 90 footers. In the meantime we were doing scaling on the 30 foot. We drove the telescope with server motors and magnetic amplifiers and we scaled this. A lot of the design work for the 90 footers on the drive and receiver system was done on the 32 foot as well. Then we picked on the Owens Valley.

Sullivan

What were the criteria that you had for a site?

Bolton

Protection principally. The Owens Valley appealed to me because the whole valley was owned by the Los Angeles Municipality and knowing that industrial development was not going to take place there.

Sullivan

Also because they had taken out all the water.

Bolton

Taken out the water and so on. I remember the meeting we had with the president of the Water Resources of Los Angeles County. Lee DuBridge and I and I think Art [Laffer?] from ONR had lunch with him, and we put our case and it looked very, very difficult. The man just had no reaction whatsoever. At the end of it he said, "Do you know I've seen thirteen solar eclipses?" So we got our site in the Owens Valley and we started to develop it. The ONR funds would only cover the operation and the personal property, and I think it was one of the directors of Bullock's who was talked into, that's a store in Pasadena, into giving us $100,000 for on-site development, the rail tracks, and the housing, and that kind of thing.

Sullivan

So you didn't get anything directly from Caltech? Except your salaries, I suppose.

Bolton

Caltech paid half my salary - that was all their contribution to radio astronomy. They charged overhead on the other half which paid for it.

Sullivan

Was there any push from the optical astronomers at this time, particularly Baade and Minkowski or were they just on the sidelines entirely?

Bolton

I got to Caltech and of course, I started this. I was given a room and a desk and a chair and at 9:00 on the first Monday morning, Rudolph came into my office and he said, "Well, I don't want to influence you, but...." And I think for the next four years Rudolph appeared at 9:00 on Monday mornings to find out how, he wanted his weekly report on how things were going.

Sullivan

So he was very interested?

Bolton

He was very interested.

Sullivan

But did he actually have any influence on, for instance, trying to get you...

Bolton

No. I mean, he was interested in the identification problem. What he wanted to make sure of was that I was doing the right thing to get what he wanted.

Sullivan

But what I'm trying to get at is that there was apparently no push from the optical astronomers at Caltech for this radio observatory. They didn't fight it, but they weren't really out there fighting with you either.

Bolton

Yes. I think Jesse Greenstein helped greatly. And some of the younger people like Guido Munch and so on. But I mean, to them it was obviously going to take us a number of years to get going, particularly on something as massive as what I was proposing. So there wasn't really the direct interest until things started to happen.

Sullivan

You say 'as massive as what you were proposing', the dishes were of somewhat different design, however, an 85 foot dish in that day was large, but not unheard of, right? There was going in at NRL and of course, the Dwingeloo dish and so forth.

Bolton

The Dwingeloo dish was the only one.

Sullivan

Well, the 84 foot at NRL, well, I guess that was a little bit later, wasn't it?

Bolton

90 footers were the first of that size to be operational.

Sullivan

Is that right? And of course they were on rail tracks, which was an entirely new aspect also. So in fact, I guess there were a lot of unknowns that you had to look into, which naturally spread out the construction time and so forth. Were there any particular troubles during construction or did it all go pretty smoothly if maybe a bit slowly?

Bolton

No, it all went very well. We had tremendous assistance from Bruce Rule and he and I worked very closely together for four years and...

Sullivan

What was his position?

Bolton

He was chief engineer at Caltech. He was essentially in charge of the synchrotron, the engineering for the 200 inch and that kind of thing. And he was, Bruce was a quite surprising person. He really wanted to understand what the scientist was doing. He wasn't the sort of person who would take 'make this for me' - he wanted to understand why it was being made and whether it was the best method of tackling the problem. And I worked quite closely with him. I used to go with him on his trips to Palomar; I helped scrub the mirror for the first successful coating that was put on the 200 inch; I worked with him on the gearing of the Lick telescope, the Lick 120 inch when it was in difficulties. So I learned as much about optical telescopes from him as he learned from our radio telescopes from me. It was one of those associations for which I'm very grateful at Caltech. Of course Bruce, when this telescope was getting to its bidding stage, when the design was almost complete, Taffy Bowen had Bruce and I go to London for a month to do a criticism of the Parkes telescope. Bruce came out here during its construction and that kind of thing.

Sullivan

So you're saying there were no particular cost overruns or lengthy delays?

Bolton

No. There weren't cost overruns, but I've always been a person who kept reasonably within his costs. For many years I used to do estimates for people. I remember one occasion I was involved in the setting up of Green Bank and that kind of thing. I was kicked off a committee which approved the 140 foot and Rule resigned from it. And I remember one occasion, I think it must have been about 1958 at Boulder, Dick [Richard] Emberson said, "John, what do you think the 140 foot is going to cost us," and I said, "Well, you won't have any change after $20 million, Dick." He said, "I've got a surprise for you - I've got bid for $4.8 million from..." and I said...

Sullivan

Your statement still stood?

Bolton

My statement still stood.

Sullivan

What was the final cost of the 140 foot?

Bolton

$19.5 million. That was after the contractors had been changed three times and the design had been changed four times.

Sullivan

When was the first, when were the first observations taken with a single 90 foot at least and then two?

Bolton

The day it was dedicated, I think, about November of 1958 or 1959. Was it ’58 or ’59?

Sullivan

I could probably check that.

Bolton

Probably November 1958. We had a working receiver on the single telescope.

Sullivan

What about as an interferometer?

Bolton

Roughly 12 months later. That was the first observations, we didn't really get working until, well, let's see, I took a few months off at that stage and we got the two dishes completed, and I came out here for Christmas and then went to Europe. It was in passing through ONR that Russell Sloanaker talked to me and showed me his...

Sullivan

You mean NRL?

Bolton

Yes, NRL. Showed me his records of Jupiter, you know, he got 400° in temperature.

Sullivan

At 10 centimeters?

Bolton

10 centimeters. And I was awfully convinced, and I rang up Gordon Stanley, I think this was in February and told him of Russell's results. By the time I got back to Caltech, which was only two or three days later, he and Roberts had found Jupiter at 960 and it wasn't 400°, it was 6,000°.

Sullivan

So Caltech got involved with the Jupiter radiation?

Bolton

Yes. And then, of course, later on when we got the interferometer, [Venkataraman] Radhakrishnan and I did the, showed that it was belt radiation.

Sullivan

Just out of curiosity, when you went to Caltech, when did you think that you would probably get something going? Did you think it was going to be four or five years?

Bolton

I thought two years.

Sullivan

But of course, you didn't know what you were going to build either at that stage.

Bolton

No, I initially had gone for two years.

Sullivan

Oh you mean you thought you'd come back after two years.

Bolton

I thought I'd get something off the ground in two years. And I had an initial two year appointment. It did spread out to, well it was very close to four, but then I expected to go with the go ahead and the money to build something. Essentially, it took over two years to overcome the inertia and I remember Jesse one day when I, Jesse Greenstein, one day when I was really infuriated at the delays that were being imposed, getting very fed up about it and Jesse said to me, "You don't have to worry, John, you're at Caltech, you've arrived." I said, "I didn’t come for that Jesse. I came to build you an observatory. I'd like to get on with it."

Sullivan

Having these visions...

Bolton

You know, things like the negotiations for the land in the Owens Valley was really protracted. The difficulties with the Navy as to whether they could own something which was not, they can have something on land. Owens Valley would not give us the land, you see...

Sullivan

The Los Angeles County.

Bolton

The Los Angeles County, the water supply wouldn't give us the land, so there were all sorts of difficulties. Three things I learned in Pasadena were union law, contract law and patent law.

Sullivan

Probably doesn't do you much good in Australia where they're all different.

Bolton

No. I mean the complications one gets into with federal funds with a nonprofit organization in the State of California with a contractor based in Arizona and so on.

Sullivan

On Municipal land.

Bolton

On land which is owned by the Los Angeles Water Supply.

Sullivan

It seems to me that from all the talking about sort of large projects that it’s not always the same set, but there's always a set of problems.

Bolton

Sure.

Sullivan

It always takes about one and a half or two times as long as anticipated.

Bolton

Yes. I had hoped to see the dishes going up in two years. Of course, when they did go up, they went up very fast because we chose a method of construction in which we specified everything. We designed it down to the last nut and bolt, instead of saying here is an outline, as a matter of fact, the scheme's got some problems that way because we had already spent a lot of money on the details of the design which many companies would have done themselves, but we still had to put up with the overhead which goes along with doing that. I mean the company the finally built 90 footers was, I can't remember the name of it, Phoenix, Arizona, built highway bridges and guardrails on the Arizona highways. But they only had one engineer on the staff and two draftsmen, but our job suited them because it was ready to go into the machine shop.

Sullivan

Well, let's talk about, before we get into the radio astronomy that came out of Caltech, let's talk about a couple of meetings and trips that you took, for instance I see here that the Manchester Symposium you presented a paper showing some variations in Hydra A which I guess in hindsight turned out to be probably not correct. Do you remember this?

Bolton

Oh yes. That was mainly Bruce Slee's work. We got certain days, I mean, undoubtedly the variations were there, and no doubt it's peculiar atmospheric phenomenon. But exactly why, I don't think it's ever been chased down.

Sullivan

But you were at Jodrell Bank, you presented that paper, but what I'm simply interested in is your reactions to what went on at this meeting. What do you think were the high points of that meeting? What are your recollections of it?

Bolton

Zero.

Sullivan

Zero. You don't remember at all the 2C results or...

Bolton

Oh yes, of course, and that was by Dublin.

Sullivan

That's right.

Bolton

Well, no, my reaction was that there was something horribly wrong, in fact, we had a special meeting one night of the IAU [International Astronomical Union] in Dublin. I mean it was just impossible to distinguish the old business, discernibility and detectability.

Sullivan

Right. So you had already been through all this.

Bolton

Right. And I just couldn't pin it down. And out of that of course, came a letter to the Observatory which I wrote, which said how it happened. This must have been the Observatory around the end of 1955. [Sullivan: April 1956]

Sullivan

Okay. I don't seem to find that one here, but...

Bolton

Maybe you can look it up in the library.

Sullivan

Well, in any case, so in this paper, you pointed this very fact out? That they were confusion limited essentially?

Bolton

The thing that I pointed out is whether you are noise limited or confusion limited. You will always get an answer which is steeper than the real slope. And the reason for this is the following: that if you say take an ideal universe, Euclidian universe with all the objects the same initial power and you get a slope of -3/2and it intersects the X-axis at some point which is based on what the average power is and what the average density is. Now then, if you then take a population of objects which has some dispersion around that absolute power, you get a line which intersects the axis further along. Now if you make experimental errors, and those errors increase as your flux density decreases, you are going to go from one line to another line to another line. And this is what raises the slope. I mean, a very crude object...

Sullivan

Right. This is closely related to the Malmquist effect, I believe, is another name for it. Namely one's sensitivity cuts this off that you get a systematic effect at the low signal noise points.

Bolton

But then back at Caltech, Westfold and me, had Westfold joined me? No he hadn't, he hadn't at that stage. I did an experiment with two graduate students. I took the 2C antenna and synthesized a strip of the sky and what we did was we had a sample of sources which would give us a log N - log S slope of 3/2, we wrote them on paper and threw them into a hat and then we took another 10,000 bits of paper and wrote source on 300 of them, approximately 300 and put them in another hat. Then the graduate students sat down and pulled pieces of paper out and when they came to a source. Oh, we had another hat, too, with some relative phases. So when they came to a source, you pick a flux out and you pick a relative phase out, and then we synthesized what you have seen with the interferometer. Now the first experiment we just took the first 50 sources out. I mean we had a listing where they come in the sky, what flux they were and what the phase relative to the adjoining sources would be, because this is important in interferometry see. And then we synthesized the interference pattern. First with the 50 sources, and the other graduate student analyzed this and he picked out, I think, 30 of the 50 sources pretty reasonably in flux and position. And then we did it again by adding it to 100 and presented him with this again, see.

Sullivan

With 100 sources now?

Bolton

Yes. 100 sources. And he picked 20 with reasonable results. And then we put the other 200 in. And I think he got 2. This was just to satisfy yourself that...

Sullivan

Didn't publish that result, huh?

Bolton

No, we didn't publish that.

Sullivan

That's too bad. It would have been known as the three hat experiment or something. Did those graduate students later go into radio astronomy, just out of curiosity?

Bolton

No, one was George Wallerstein, I think.

Sullivan

Really?

Bolton

I couldn't be sure of that. George did work with us to a certain extent. It might have been George.

Sullivan

So you said there was a special evening meeting at Dublin, what took place at this meeting?

Bolton

This was the IAU in 1955 at Dublin, in which Ryle gave his results and Minkowski and I got very hot under the collar. I mean, 2C produced a slope of -3.

Sullivan

Yes, right. But why did Minkowski get upset?

Bolton

I think Minkowski was very well aware of confusion. Minkowski worked with all the data that came out, trying to identify. He and I talked on the philosophy for the 90 foot dishes. You've really got to pull the source with a primary beam before you can disentangle it with the interferometer. I mean, he...

Sullivan

Right. But now, hold it, this is the summer of 1955, before you'd gone to Caltech.

Bolton

Yes.

Sullivan

So you...

Bolton

No, I was at Caltech then.

Sullivan

You'd been there for a few months before...

Bolton

Yes, I'd gone there in January of 1955.

Sullivan

Oh, I'm sorry. So you'd been discussing these issues?

Bolton

Yes. Yes.

Sullivan

That's interesting, because I see him as one who is very interested in radio astronomy, but not as one who might appreciate the subtleties, such as confusion and how it works.

Bolton

Yes. Minkowski was trying to identify things from the Mills survey, from the 3C survey and so on, and I was arguing all the time, you know, the inherent accuracy is just not there. This is what we're going to... this is where we, this is what we're building this for.

Sullivan

He wasn't finding anything?

Bolton

He wasn't finding anything. And I knew he wasn't finding anything because there was nothing to find.

Sullivan

Okay. That Green Bank Meeting was also the one where the Russians claimed the deuterium line.

Bolton

Yes. Well, that stimulated me to get Stanley and Price to publish their results.

Sullivan

To write that up? Yes. Let's see, during this chronological period, in terms of publications, the next thing I find is Bolton and Wild, I believe, where Paul Wild just told me about this last week, where he just happened to be passing through and... but nevertheless, I'd like to hear your side of the story. How did this idea come about with the Zeeman splitting?

Bolton

Well, Paul, I think was spending some time at Harvard and I'd invited him to come to Caltech and spend something like, six weeks he spent with us there. He was coming up to Palomar to do some observations or get some, help get the thirty foot running. Paul was there when we got the 30 foot running at Palomar and also when we opened the Owens Valley site. I don’t remember whether he spent six weeks or three months with us at the time, but Paul had, he visited Mt. Wilson the day before and seen Horace's solar magnetograph.

Sullivan

Babcock?

Bolton

Babcock, Horace Babcock's solar magnetograph, and we went, we drove, the idea came to us when we were driving up to Palomar and we began discussing, I think, the question as to whether one could see the hydrogen 21 cm line in our own atmosphere in absorption against the Sun. And we began to think of all the things which would blur it out, and the Zeeman effect one of them. Paul is sort of a little more theoretical than I am and has numbers in his head and we worked out that one Gauss the Zeeman...

Sullivan

2.8 megahertz per Gauss, I think.

Bolton

Per Gauss would wipe out any possibility of seeing hydrogen in the space between us and the Sun. And I forget which one of us said what about the Galaxy? And of course, Paul had seen Horace's system and the two things together made, the detection of intergalactic absorption and...

Sullivan

Interstellar you mean.

Bolton

Interstellar absorption possible, and I think at that time, Ed McClain had got the first 21 cm with narrowing off profiles.

Sullivan

Yes, that had been around for a year or two at that time, with quite a narrow profile.

Bolton

That's right. And so we decided it could be done and we wrote that paper.

Sullivan

And Paul had written that theoretical paper on the hydrogen spectrum, but also I was interested to learn earlier today that you had had an interest in the hydrogen line even though you never published anything on it, in fact, this may be your only publication on the hydrogen line, I'm not sure. I was always wondering how that came out of the blue. But it seems like mainly during these four years there wasn't time to do any research here. You were sort of totally preoccupied with getting the observatory going.

Bolton

Oh, we did quite a bit. We had low frequency array at Owens Valley.

Sullivan

Oh, you did?

Bolton

Barry Clark and I, I think, published the first observation of the Crab Nebula by the Sun.

Sullivan

Stanley and Clark? Bolton, Stanley, and Clark?

Bolton

That's right.

Sullivan

'58 PASP [Publications of the Astronomical Society of the Pacific] "Lunar Occultation of Taurus A at 12 Meters," I see.

Bolton

Solar occultation.

Sullivan

Oh, I had lunar written here, but you're right. No, that was not the first.

Bolton

No, it was not the first, but it was the first really good one.

Sullivan

Okay.

Bolton

I think Vitkevich had done some.

Sullivan

Right. And Cambridge, they'd also done a couple.

Bolton

Yes, but this was the first one at very low frequencies.

Sullivan

At Dwingeloo even before the antenna could be fully moved, they put one together.

Bolton

Ours showed something like a two week occultation, we saw the parameter out to about 15 million miles.

Sullivan

Because you were at such a low frequency. And what was this antenna? What did it consist of?

Bolton

Dipole arrays in the ground.

Sullivan

Did you do anything else with that?

Bolton

We did, what was your question?

Sullivan

Did you do anything else with that Dipole ray besides see occultation?

Bolton

Yes, we started, tried to determine how much of apparent scintillation an interferometer was phase and how much amplitude.

Sullivan

From the ionosphere?

Bolton

Yes.

Sullivan

And you were telling me that that in fact, never got published because you...

Bolton

No, we were interested in that because I had consulted on low frequency, low angle effects with the people who were interested in the direction of space vehicles which were to come. This was before the days of inertial guidance, and also, we wanted to devise fringe tracking equipment for later 90 foot interferometers.

Sullivan

So this was good training for someone like Barry Clark?

Bolton

Yes. Barry was with me for a very long time. He started work in his first year as an undergraduate.

Sullivan

Oh really?

Bolton

Yes.

Sullivan

I didn't realize that. So he was a freshman when you arrived, you both came to Caltech at the same time?

Bolton

Well, he got a summer job with me doing survey work and digging post holes.

Sullivan

What about the 30 foot dish which you've already said is primary purpose was as a model for the larger dishes, but it did do some hydrogen line work. Seems to me that it was just sort of filling in, I mean, it was just minor projects. Would you agree with that?

Bolton

Yes, with the 30 foot, we did a survey, I forget, what declination range it covered, but we did survey actually as far as we could get into the southern hemisphere.

Sullivan

I think you went to 294.

Bolton

Yes. We extended Dutch HI survey down to...

Sullivan

But you didn't do any analysis of this really, just...

Bolton

No, I mean...

Sullivan

Your heart wasn't in it is what I mean. You were just killing time in a sense.

Bolton

Yes. You've got to do some observing to find out how good or how bad the hardware is, and of course, as soon as things started to move on the construction of the 90 foot, the whole effort transferred to the Owens Valley.

Sullivan

Well, okay, let's talk about the first experiments that were done with the 90 foot. I think even before the interferometer was ready, there was the single dish worked on, is that right?

Bolton

Yes, one of the very first observations was the one I referred to on Jupiter. And we first of all started off to make a finding list of sources for work with the interferometer to find out what their fluxes were. We originally started off on, we had the idea of 400 megahertz, when we started. Now what changed our minds, I think, was the ability to make good switches at much higher frequencies when the RF diodes came in. And we had mechanical switches for 400 but these are [?] when we went to higher frequencies, so actually the first observation I think, we done at 700 megahertz, and within just a few months, we transferred to 960. The reason for 960 was that it a frequency reserved for satellite communication.

Sullivan

I see. That didn't lead to any problems later on when there were...

Bolton

No. No.

Sullivan

Many satellites.

Bolton

In fact the first receiver that was 960 which was the Vanguard and the Vanguard station was directly copied from from Caltech design.

Sullivan

And you say the Jupiter thing was one of the first. When you found out at NRL they had discovered a very high brightness. And I have here [Robert W.] Wilson and Bolton, I'm sorry, that's another paper. So you weren't on that paper because you were away, is that right?

Bolton

That was Stanley and [James A.] Roberts who wrote about Jupiter. I would say they did it.

Sullivan

Right. I talked to Jim Roberts about that.

Bolton

Yes. In general, one of the staff members at Caltech took one of the students and although we all worked together to a tremendous extent, for example, the work which [Alan T.] Moffet and Morris did on anglicized sources, for example, each time we moved a 90 footer to a longer base line, we had additional problems and Bob Wilson and Radhakrishnan and Jim Roberts and...

Sullivan

Ken [Kenneth I.] Kellermann?

Bolton

No, Ken was a bit later. Alan Moffet and I would go up and we would make the thing, solve all the problems for making it work on the next base line and we'd do some Jupiter work and then we'd leave it to Moffet and [David] Morris to continue with a couple of weeks observation and then they...

Sullivan

It was a real group effort?

Bolton

The [brains trust?] would come up later. In general, one staff member was associated with one student. I mean, there were student projects really, so you had Roberts and Harris who produced the CTA catalogue, which was mainly false findings, 3C sources, Bob Wilson and I did galactic plane survey, later on Radhakrishnan and Barry Clark did the hydrogen line detection work and so on. So it's generally one student and one staff member.

Sullivan

Well, besides from the Jupiter, what do you look upon as the main results that came out of the early years at Owens Valley?

Bolton

I think everybody did, all the projects did something useful. Moffet's thesis, the work Morris and Moffet did essentially said- you know, gave us the statistics of the radio source population in terms which they proved that it was no fluke that Centaurus was a double and Cygnus was a double. Many, many sources had multiple structure. That was one thing that came out of it. The Jupiter work, demonstrating in fact that Jupiter had a sort of super Van Allen belt system. The work by Radhakrishnan and Clark on the two temperature interstellar medium, I think this is a rather fundamental thing. And last but not least, the improvement in the source positions and the identifications which we got.

Sullivan

So the CTA survey was to check 3C positions?

Bolton

Well, we had to have a finding list for sources, and so Dan Harris and Jim Roberts started out to find out where the 3C sources were so that we could point the primary beam of one dish at them and then work at it with the interferometer. Actually, of course, Ken Kellermann always claimed that I set astronomy back ten years by following up 3C sources- what we should have done was an independent survey and discovered all the high frequency phenomena which later, of course, we exploited very much at Parkes.

Sullivan

But what you found is that these sources are reliable, but often shifted by a lobe or two?

Bolton

It would often take a whole night to find a 3C source, because your [?] lobe positions were not necessarily correct. The most likely thing is for a lobe shift, that is the source is completely isolated within the 3C antenna system and it's not isolated so fractional lobe shifts, all the fractional lobe shifts come in. So in fact, one really had to survey something like 5° square.

Sullivan

I see.

Bolton

Say 5° x 2° to find the 3C source and this is where the odd sources like CTA 26 and so on with the peculiar inverted spectra as they now know came from. I mean, they were the other things that were found along the way. So the CTA survey is mostly 3C sources, but also picked up quite a few high frequencies.

Sullivan

CTA 102, also?

Bolton

CTA 102, yes.

Sullivan

So you concluded, was it you then concluded about the reliability of the 3C survey?

Bolton

Well, we'd have saved ourselves a lot of time by doing the survey in the sky.

Sullivan

Right. And is this work, you think, what convinced the Cambridge people to have a 3CR, or how did that come about?

Bolton

I don't know how the 3CR came about, but they only had to look at the CTA catalogue to find out how bad they were.

Sullivan

There was no one else checking these positions?

Bolton

No.

Sullivan

No one else could really, I guess.

Bolton

No. Of course, when the objects were isolated the Cambridge positions were very, very good. At least in the right ascension. And we did lean on the Cambridge results and I suppose the two prize identifications that came out of Caltech in the days when I was there were 3C295, which Minkowski got the richest record which has stood...

Sullivan

Until a couple of years ago.

Bolton

Until a couple of years ago. And 3C48. Now we really depended upon the cooperation of two observatories for that. As I said earlier, even before I went to Caltech, intuitively I felt that one could describe, if you had a source which was so many minutes of arc in diameter it was a galactic source of that size, or an extra-galactic source much smaller. Now one of the things we wanted were fundamental calibration points in the sky for the interferometer, and high declination sources where we could measure declinations fairly accurately. Right ascension depended, of course, upon [?], a reason you can make a declination very accurately is because you observe a source near zero. Your error in your base line parameters is so small on the period method. But we were looking, you see, radio galaxies, for example, work we'd done on structure. It was quite clear from Moffet's work that the optical center and the radio center didn't necessarily coincide. Quite obviously, the further you put something away, the less error you make in the assumption that the radio center is the optical center.

Sullivan

Yes, that's right.

Bolton

And so we took sort of major effort, the four sources which the Manchester people had been unable to resolve out with their longest base line interferometer, one of them was C295 and the other was C48.

Sullivan

Right, I think they had less than 10 arc seconds sort of sizes.

Bolton

That's right. Now, in the case of 3C295, our right ascension and the Cambridge right ascension were almost identical, and this said to us that neither of these systems which have totally different primary beams is affected by confusion. And this was enough to talk Minkowski into going after the spectrum of 3C295. Now once we had 3C295 we had fundamental calibrator for a right ascension, and the next source we attempted, well, we attempted a detailed analysis of many observations and the mean and everything like that, was 3C48. And, of course, 3C48 came out in 16th magnitude star and if it wasn't that 16th magnitude star on the Schmidt plate that 16th, the image of that 16th magnitude star was indeed covering up something.

Sullivan

What sort of error box did you have for your position for 3C48?

Bolton

About five seconds, which you see, is the size, is less than the image size.

Sullivan

Which is highly unusual to find a 16th magnitude star...

Bolton

Yes. Now 295 I think we had something like five seconds of right ascension, that’s combining our position with the Cambridge position, and something like 15 seconds of arc declination. And this, in fact, included two galaxies. And Minkowski got a spectrum of them both.

Sullivan

Continuing with John Bolton on 15 March ’78. The reason that so few identifications were made on the original 3C survey, for instance, [David W.] Dewhirst was at Caltech at that time, as I'm sure you remember...

Bolton

Oh, yes.

Sullivan

Was simply because of these very large effective error boxes despite the low formal errors in positions.

Bolton

That's right. And of course, Dewhirst did get a few identifications.

Sullivan

He got a few, yes, but a very low percentage of the overall catalogue. So then, what was made of this 16th magnitude star? This is 1960, I believe?

Bolton

Yes. Well, it was initially very hard to talk anybody into doing anything about it.

Sullivan

Even to look at a spectrum?

Bolton

Yes. And Rudolph Minkowski had retired, of course, by then. It was his last run on which he got the redshift of [3C] 295 and actually Jesse Greenstein was the person that we said, "Jesse, you've got to do something about this, or else." And Jesse did, or he attempted to, it was actually the first time he’d ever been in the prime focus cage.

Sullivan

I see.

Bolton

And unfortunately, he was clouded out. And so it was Allan Sandage- Allan was a lot more junior then than now- who was told by Jesse to get a spectrum of the thing. And, of course, nobody could recognize the spectrum, and everybody- well, we had the idea when it was found that here was start of something optically. The general idea when we got it was that here was something very, very distant. That it's the bright flash in a galaxy which ultimately leads to the standard wide double radius source. But, of course, at that time, nobody had any knowledge of what the ultraviolet spectrum of anything looked like- rockets hadn't flown.

Sullivan

Did this flash business, of course, is just a bit of speculation, in those days?

Bolton

Yes, pure speculation. But this was a flash, we were seeing the optical phenomenon.

Sullivan

A few million years later maybe the radial lobes will be there.

Bolton

That's right. And well, a large number of people attempted to solve the spectrum. I, indeed, did get the right answer for the redshift of 3C48, and I had forgotten till quite some years later when Fred Hoyle reminded me- he came into my office one lunchtime and- Fred used to spend three months each year at Caltech- and I said to him, "Well, either the redshift of this object is .36 or I don’t know what it is." And indeed, I had the line identification right, but the wavelength fit was not very good. Of course, nowadays, one just doesn't worry because you know that the emission lines in quasars are chopped up on one side if it’s a permitted line, they're chopped up by absorption lines.

Sullivan

But you had to be very conservative on this thing.

Bolton

Yes, we had to be very conservative, but, in fact, well certainly Matthews and I were convinced that it was something of super luminosity. But, of course, until the later stage of 3C273 at Parkes, people were starting to, well, Jesse Greenstein and Maarten Schmidt had written a paper to explain how a star could produce these lines at these wavelengths. The idea had been dropped, of course. I think about 4 or 5 founded with peculiar emission line spectra or no emission lines at all in the Caltech search. The reason we never got 3C273, I mean it would have so much easier if we'd identified 3C273 at that time because its spectrum is very obvious- here's the hydrogen line staring you in the face. But, of course, 3C273 has the same right ascension as M87 and M87 was observed every day with the interferometer, it was one of the fundamental calibrators, and so 3C273 was...

Sullivan

I hadn't heard that story, that's interesting.

Bolton

That's true, and later when we come to the Parkes dish, the position I set on the telescope for the lunar occultation of 3C273 was the position that came from the occultation.

Sullivan

But why couldn't you observe off the meridian?

Bolton

We tried to catch one observation on the meridian always, and I suppose we could have done it, but M87 was the fundamental thing- what's happening to the drift in our cables and that kind of thing.

Sullivan

So you always caught it at transit.

Bolton

We always caught M87.

Sullivan

And 3C273 was just another 3C source- or is that true? That there was no particular need...

Bolton

No. Just another 3C source.

Sullivan

I'm confused now, was it not one of the Jodrell Bank very small sources?

Bolton

No.

Sullivan

It was not. Okay.

Bolton

In any case, its declination was rather low. And it would have been a challenge to get its declination with the Caltech interferometer at that stage.

Sullivan

You were concentrating on the ones you could do better?

Bolton

Yes.

Sullivan

But was there any published record of this toying around with such horrendous redshifts in that day and age?

Bolton

No, I don't think so.

Sullivan

I'd never heard that anyone had really ever come up with a possible number before Maarten Schmidt’s.

Bolton

The lines one could see in 3C48 were Mg II, Ne IV and oxygen 3727.

Sullivan

No hydrogen lines?

Bolton

No. In fact, I think it was only 3727 and Mg II, those two lines. 3727, of course, is forbidden and Mg II is not.

Sullivan

Yes. Just looking at the other papers to 1960, in which you’re a co-author, let me see if there's anything we haven't discussed. You actually published a paper with Radhakrishnan on H I absorption on the Owens Valley interferometer in 1960.

Bolton

That's right.

Sullivan

Where did the idea of doing interferometric H I absorption come from? Were you thinking these must be small clouds or...

Bolton

No. The interferometer was always envisaged to do H I absorption measurements. Simply because one isolates the source and then you avoid the difficulty of having to subtract. An average emission profile of the surrounding region from the absorption profile, in fact, our first observation which Radhakrishnan and I ever did get totally different profiles from the single dish profile. We'd said the structure between, the emission structure in between fringe size and our single dish size, in fact, Rad later stages where he successfully using the interferometer here.

Sullivan

At Parkes, yes. So you're saying as soon as NRL showed that there were these narrow absorption lines that it was clear to you that this would be a good thing to do with an interferometer.

Bolton

Well, the point was that one could only observe sources which gave you antenna temperatures which were in the at least in the tens of degrees, because you faced the emission break down of 100 degrees. If you were ever going to work large numbers of sources and determine what the sort of interstellar background looks like in many directions, and wanted to work on sources which have antenna temperatures of 2° or 3°, then you had to go to interferometry.

Sullivan

Were you thinking in these early, you know, 1957, 1958 were you thinking that, indeed, you might come up with a different kind of gas? Sort of thing that eventually happens- that you might be finding a different component of the interstellar medium?

Bolton

Yes. I was convinced of that in 1955.

Sullivan

That these clouds were...

Bolton

That there must be hot and cold clouds. In fact, Rad and I, Rad published in the PASP- did find self-absorption at one stage, which coincided with the dark lane, we found this near IC443. Actually found self-absorption in the emission background. But that was before we had the interferometer going. This is now very familiar - cool clouds of molecules...

Sullivan

Then, of course, it was not a standard concept at all. Well, this is all the publications I have to 1960 before we come down to the Parkes antenna. Are there any other aspects of Caltech that should be covered?

Bolton

Well, Caltech never sort of continued in the very successful run we had in 1959 and 1960 era.

Sullivan

You mean after you left?

Bolton

Yes. And Caltech is principally to blame for that. They had a very keen crew of graduate students, people like Ken Kellermann and Barry Clark and Bob Wilson and so on. But unfortunately, of course, Caltech would not appoint another director.

Sullivan

Was this basically a financial reason?

Bolton

No, I don't know why. I really don't know why. Minkowski and Baade had gone. So the pressure from optical side was lacking, Caltech wanted somebody with a big name. I made two suggestions as to who should be the next director, one of whom was finally appointed, Marshall Cohen. If Marshall had been appointed when I left, I think it would have gone on from strength to strength. The other was Bill Erickson who had worked with us to quite some degree, but you see, it left Caltech with nobody who could say, argue with people like [?] and [?] and Mike Bowen and so on. Gordon Stanley very reluctantly- he never wanted, I mean, his interest was purely from the technical side. And it unfortunately died to a certain extent. It still continues but...

Sullivan

The thing that sort of interests me is that with these two movable antennas, you had the possibility to do what is now called Earth rotation synthesis or super synthesis. Did this ever occur to you people in those days or were you just so fixed on just getting sizes and positions that this was outside of your realm?

Bolton

We used two antennas as very flexible single experiments. In a way, we did synthesis. I mean, Moffet's work on angular sizes is synthesis.

Sullivan

Right.

Bolton

But at that stage, we had 100 or 200 sources on which we could get detailed information. And...

Sullivan

You wanted to do that first before you spent a lot of time...

Bolton

Time...

Sullivan

One single map.

Bolton

That's right, yes. And the other problem, of course, is the tremendous effort one has to put in on the computing side.

Sullivan

Although at Caltech I would think if anywhere there must have been some good computers coming along by the late 1950's.

Bolton

Yes, this is true, but you've got to get computer data recording and...

Sullivan

Right, and you've got to develop all the software...

Bolton

Everything like that. We were, by no means, we were doing the easy experiments.

Sullivan

Okay, so then Taffy Bowen offered you, what was the official title of that position? Directorship of the Parkes Observatory?

Bolton

Yes.

Sullivan

And you came down here in what year?

Bolton

At the end of 1960.

Sullivan

’60, so the year before the dish went on the air?

Bolton

It was before it was built.

Sullivan

Before it was built? Was it late in 1962 before it went on the air?

Bolton

No, late 1961.

Sullivan

Oh, it was built that fast?

Bolton

Yes. Just the tower was here when I came back.

Sullivan

Okay. And what was the program you were envisaging for the dish?

Bolton

Well, one of the things we could not do very successfully at Caltech was to employ the whole of the radio spectrum. And this is one thing, I mean, we didn't have the collecting power at very short wavelengths. We didn't have the resolving power at long wavelengths. I mean, Caltech was ideally suited to, say, around 21 cm region, where one could see the collecting area being useful as short a wave length as 10 cm and the resolving power useful at wavelengths as long as, say, 70 cm.

Sullivan

Did you have enough staff to maintain such a wide stable of receivers? Also, at Caltech if you’d had...

Bolton

No, Caltech's primary resolving power and collecting area, the collecting area, you see, sensitive receivers change very radically so one almost has to look at the epoch. We were struggling past 21 cm even though we sort of got experimental traveling wave tubes at 10 cm and towards the end, the maser possible, but we really had to go to 1 gigahertz to get adequate resolving power in our single dish, so what I principally saw in Parkes was the possibility of using a very much bigger bite of the radio spectrum.

Sullivan

I see.

Bolton

And, of course, in my, well John Shimmins and I found that one could, in fact, distinguish what one was looking at through the spectra. There was a 99% chance of flat spectra object in the quasar and [?] so one can do some sort of blind astronomy.

Sullivan

But that wasn't clear when you came down here in 1960? Or were you thinking that maybe...

Bolton

Well, we didn't have at that time, we didn't know what we could do if we used the whole spectrum. And Parkes offered me the addition.

Sullivan

It just hadn't been investigated.

Bolton

In any case, I was committed to come back here quite some time before I did come back. Taffy was over for the dedication of the 90 footers and was very impressed with them and everything like that and he said, "I suppose you're here for life." And I said, "No. I'd like to come back when things are running properly." And he said, "Well, [?] the job is yours when you want it." Of course, the pressure came on me a little early, we were really having a very successful time at Caltech when Taffy began to make noises that I should be here when the dish starts to go up. So I really...

Sullivan

So you would have preferred a little bit better timing.

Bolton

I would have preferred another year at Caltech as it happened, but there were other things which, you know, our kids were getting to the stage where, were leaving school and that kind of thing, so from a family point of view, it definitely changed things.

Sullivan

So the Parkes dish itself, I talked to people like Harry Minute and so forth and it seems that the construction went very smoothly and very fast - even finished before you expected, it's almost unheard of once it started being built. And your program then was, from what you said, to look at spectra of...

Bolton

Well, no, I don't think the Directorship of Parkes was very different from the Directorship at Owens Valley. The Directorship of Owens Valley was, in fact, building the equipment and directing its research program. In the case of Parkes telescope, it was principally getting the antenna going and finding people to use it. And I certainly had no expectations of doing anything, personally, with it. My main job was to get it built and then to get it operating. And of course, when I came back, we still had the many small groups and really, there were very few people who even conceived of using the Parkes dish, you see, because it was something quite unreal to most of the lab. But, of course, many people from Radiophysics had gone overseas. Roberts was with me at Caltech and he came back with me. Radahkrishnan and Morris came to Australia from Caltech. Mathewson came back from Jodrell Bank, Ryan Robertson came back from Leiden and so on, but I mean, the people who were really wanting to use the dish- well, Frank Kerr, Tom Mathewson, who just arrived back, you see. Frank Gardner was the only sort of local radio physics person who, in addition to Frank Kerr, who had ambitions on the 210.

Sullivan

Because people were not oriented towards large...

Bolton

No, they were not oriented. They didn't think of it. And they all had their own little field stations. And actually no provision made for even operating for the 210, and I went around first or second year after it had been built, visiting closing field stations to get some...

Sullivan

Get some operating funds.

Bolton

You had to employ the man who cut the grass and that kind of thing. We were very short of funds.

Sullivan

So really, it was a very big change in style, the whole way the lab operated.

Bolton

Yes, it was a very big change in style.

Sullivan

And which, obviously, makes for various sort of adjustments.

Bolton

Of course, we had a number of almost immediate successes. And that sort of gradually changed the whole pattern. People who didn't want anything to do with it either had a bad time, or drifted away, you see, even Pawsey quit. Unfortunately, of course, he died shortly afterwards.

Sullivan

That was before the dish went on the air, was it not?

Bolton

It was round about that time. I think Pawsey made up his mind, well, he went to investigate Green Bank about six months through construction.

Sullivan

Yes, right.

Bolton

And then he fell ill and was out of action for oh, perhaps, another nine months. But he was in on the Faraday rotation work.

Sullivan

The planning for it?

Bolton

No, no, I mean he saw the results of that.

Sullivan

Oh, I see.

Bolton

I forget whether he, yes he saw the 3C273 occultation results, but I mean he was an invalid by then, and I would go to his home and tell him what was going on.

Sullivan

You seemed to be showing more enthusiasm for these sort of things?

Bolton

Oh, yes. One of the things that I very greatly regret, actually, was I had built the polarization equipment for this dish, it was modeled on Caltech, and Joe wanted to use it on a much smaller dish to see if he could find polarization in a general background. And I refused to let him have the equipment. And, of course, the Dutch got that first. He could have found it if I had only let him have the polarization equipment.

Sullivan

What sort of frequency was this?

Bolton

This was a 400. The reason I refused to let him have it was that I had a lot of effort in designing it, making it work and everything like that. It would have had to be chopped up and mounted on something and by that time we were well into this construction and it was one of the things I had...

Sullivan

Was it a small dish he was thinking of?

Bolton

Yes. A small dish, 15 foot dish or something.

Sullivan

Interesting. Well, I think, the 3C273 story would be a fitting end to the scientific side of things anyway. Could you tell me about how that came about? As you saw it from the director's point of view. I don't believe you yourself were involved.

Bolton

Yes, I was very involved. I directed the experiment.

Sullivan

Oh, I'm sorry.

Bolton

Well, Cyril Hazard came out to Australia to work with the Sidney University group about the same time I came back from 210 and I'd known Cyril for a long time. Cyril came into Radiophysics one day with the results of a lunar occultation; the only really successful lunar occultation he'd done with the Jodrell Bank telescope. Many people, of course, had had the idea of doing lunar occultations. We tried one at Caltech with the interferometer actually prior to Cyril. And Cyril showed me the results of those and even though he didn't get an identification still of one unidentified 3C sources, the potential of the technique was very, very obvious, and I invited Cyril to make use of the 210 for it.

Sullivan

What was the technical difficulty, for instance, of Caltech? You say you tried one.

Bolton

Well, we tried it on a 3C source which was in the wrong position.

Sullivan

Okay. You didn't try it on ones you had good positions for.

Bolton

Well, I mean, this is one which we hadn't positioned; it was a prediction from [?] office, we had to cut out the Moon with the interferometer and we did that successfully. But when we came to make the actual observation, we got no results and we later found in hunting around the 3C source was [?].

Sullivan

I see.

Bolton

But we got this prediction list, oh that's [?] yes. Only a week to plan and get the dishes in the right place to cut the Moon out.

Sullivan

It was just sort of a quickly done thing.

Bolton

Yes. It was done on a level of sensitivity which we couldn't easily see the source directly, but could easily see it in lunar occultation. And, of course, 3C272 was one of the sources which occultation was predicted for, I think, '62. Yes, 1962. John Shimmins was assigned to help Cyril because it required some tricky dish driving and John was responsible for the telescope drive system and Brian [?] was assigned because Brian and I had built the two receivers which were going to be used.

Sullivan

You were tracking the limb of the Moon.

Bolton

Yes. Well, no, the signal was made to track the source.

Sullivan

So why was there tricky dish driving?

Bolton

Why was there tricky dish driving? There was tricky dish driving because all these occultations occur outside the limits of the telescope.

Sullivan

Oh. Below the minimum [?] elevation.

Bolton

Yes, and I think the first one, we actually had to use offset feed for it. And the first occultation, it was the first occultation was bungled. They didn't get anything.

Sullivan

On [3C] 273?

Bolton

Yes. And so I decided the second one which was the most promising one because we looked as though we should get both the inertion and emersion. I took charge of the dish and well, it was rather I took the precautions which we later took for the Apollo missions and so on, of doubling everything, practice runs and two clocks, two recorders. I forget what happened, I think, you know, a silly thing like the ink running out on the recorder had blown the first one. And so it was a military operation.

Sullivan

Yes. More like an eclipse.

Bolton

Interference, the site was closed the roads were blocked.

Sullivan

Oh, really? Then what?

Bolton

Oh yes, the telescope and everything was closed for three days beforehand so that nothing went wrong. We were prepared to...

Sullivan

Why did you attach so much importance to it?

Bolton

I don't know. Well, I suppose it irritated me that it had been missed, it wasn't going to be missed again.

Sullivan

Okay.

Bolton

Of course, it was very successful and I suppose the extreme length to which I went was that Cyril and I flew back to Sidney on different aeroplanes with the records.

Sullivan

But only one person had the record...

Bolton

No, everything was duplicated.

Sullivan

Oh, I see. You had two strip charts and everything.

Bolton

I think we had four strip charts. Clocks were duplicated, everything was duplicated, timing, everything, was duplicated.

Sullivan

I think you meant you just had back-up in case the one failed. You ran them all, too. You must have had some unconscious premonition about this is going to be important.

Bolton

Well, you see, Rudolph was here. Rudolph Minkowski. And Rudolph had sent to Caltech for his plates of the region of 3C273.

Sullivan

To date there was only one quasi-stellar or had...

Bolton

No, there'd be half a dozen. We didn't know what 3C273 was, but the position which we determined with this dish prior to the occultation said on Rudolph's plates it's either that star or it's that jet. We couldn't determine...

Sullivan

Either way it was very interesting.

Bolton

Yes. And of course, it turned out to be both.

Sullivan

Yes. What sort of accuracy did that result in? In the position of the source?

Bolton

About 1 second of arc. But you see, the position we sat on the dials for the occultation was the position which the occultation said it was.

Sullivan

Was that how it turned out actually?

Bolton

Yes.

Sullivan

I see.

Bolton

But we said mid-way between the jets.

Sullivan

You didn't change the position, you just changed the error bars.

Bolton

That's right. The occultation gave us a structure which said it's a star and a jet.

Sullivan

Well, let me just go back and ask a couple more general questions. First of all, you mentioned this trip in 1950 where you visited Leiden and other places. I was wondering if you could just give me some idea of your impressions about the efforts that were going on at other places and the reception you got as one of these?

Bolton

Well, as I said prior to that I had written, I had corresponded with Oort and Linblad and with Minkowski and Baade. I went to England to start with and Westfold, actually went to Oxford at that time. I made Oxford my base and from there Westfold and I made forays and to various astronomical centers in Europe. At Leiden we spent quite a long time, we lectured at Leiden in the summer. We went to Keel, we went to Paris, and became great friends with the French early group [Jean-François] Denisse, [Emile-Jacques] Blum, and [Jean-Louis] Steinberg and so on. We went to Sweden and saw Linblad and [Olof E. H.] Rydbeck. We went to Denmark and saw [Bengt] Strömgren. He's been a close friend for many years, also.

Sullivan

That seems rather odd to me. Strömgren was a very classical stellar astronomer, why would you go to see him?

Bolton

I think I was interested in knowing these people. I had read their papers and so on. Where else did I go? We went for the URSI meeting in Zurich. In Cambridge, of course, all those problems with Ryle but I got to know Fred Hoyle and Hermann Bondi and Ray Littleton very well.

Sullivan

You say 'all these problems', what were they?

Bolton

Well, of course, we get back to where we talked about scintillation.

Sullivan

Oh, that right.

Bolton

I had corresponded with Ryle and so forth.

Sullivan

He hadn't told you about...

Bolton

Didn't tell me about it at all. And I wrote...

Interruption

Sullivan

You were saying you were talking with Ryle about what?

Bolton

Yes, and when I got to England I went around various places and finally I wrote to Ryle and said that I was hoping to come over for the May week or couple of weeks around the May week, which is sort of end of the term and boating activities and lots of celebration at Cambridge. And I got a reply back from Bragg, who was then director of Cavendish, saying that Ryle had told him of my visit and I should understand that Ryle's group were doing research which was in the forefront of world work and the group was pestered by hundreds of visitors and...

Sullivan

Incredible.

Bolton

And he was sorry I couldn't come.

Sullivan

Really? From Bragg. So you didn't?

Bolton

Oh, yes. I went for a month.

Sullivan

At Cambridge?

Bolton

Yes, there was a very big stink over it and, of course, it got all around the university and everything like that I was made very welcome by anybody who didn’t like Ryle.

Sullivan

So you just showed up in the hallways and started talking to people?

Bolton

Yes, well, I hadn't actually met Fred Hoyle except for one occasion during the war, but I'd had quite a bit of correspondence with Fred on various things. The attitude of the Cambridge mathematical group and so on was totally different from that of Ryle.

Sullivan

But what I'm getting at is did you visit the radio astronomy group?

Bolton

Oh, yes, I did. As Ryle realized afterwards, he'd made a terrible mistake and went and saw George Bexler, who was the sort of Dean of Australians in Cambridge, to back him up that he'd done the right thing and George told him he certainly hadn't.

Sullivan

I see, so in this way contact was made although it was undoubtedly strained.

Bolton

Oh, yes. And, of course, I met Graham Smith and John Shakeshaft and we've been friends for years out of that group- Ryle's a very unfortunate person. I remember one incident, I think I was having dinner with Fred Hoyle in John’s [Sullivan: College], and there was discussion at the table about it and a professor of anatomy whose name when I was a student was Sex Harris because he always began his first year lectures by writing SEX in 6 foot high letters across the board. He pricked up his ears at this conversation and looked across the table and said, "You know what's wrong with Ryle?" And I said, "No." He said, "His mother was an Anglophobe Dutch and his father was a medical failure who accused everybody else of plagiarism."

Sullivan

At Leiden I was thinking you must have discussed at great length models of the galactic radiation because Westerhout and Oort were working on this. I guess they had just finished publishing their paper at this time.

Bolton

Yes. We'd done, Westfold and I had done similar things to Oort.

Sullivan

Were there any points of disagreement?

Bolton

No. You were asking earlier why I went to see Strömgren. I mean one of the things that Westfold and I realized was the importance of free-free absorption in modeling at the wave lengths we were interested in and nowhere in the literature could we get a really good handle on the interstellar electron density. And we corresponded with Strömgren and we corresponded with Lyman Spitzer. It was both density and temperature we wanted. And Lyman had written two papers, one was a thing with all the phenomena which heat up the interstellar material and the other one was all the phenomena which cool interstellar material, and paper three was promised and actually it was never written. Paper three was how you put it all together and you get temperature and density of interstellar material. So that was one of the reasons for talking to Strömgren.

Sullivan

And what was the conclusion- you were at 100 megahertz then?

Bolton

We were at 100 megahertz.

Sullivan

What did you conclude?

Bolton

Well, I think our conclusions were probably that it didn't matter that much except at very, very low latitudes.

Sullivan

It was such a broad beam that would dilute the effect.

Bolton

Yes, but unfortunately it is an important effect. But we were looking to develop our work by modeling widths of the radial and z distribution of absorption. We never got around to that, we just playing with the idea. Where else did I go in Europe?

Sullivan

But let me just go back, were there ever any major differences in outlook as to the source of the galactic radiation between your model and Oort's ideas at that time?

Bolton

No, I mean, we both attributed it to essentially an unknown origin. Kevin and I called it radio stars, but that was just a volume emissivity element except one couldn't be quite certain. As I said, we later came to the conclusion that the density was that of the electrons. It wasn’t stars. To a certain extent, the teaching at Leiden was based on a lot of work that Kevin and I had done, spherical integration methods, concept of antenna temperature and so on. These were really devoured at Leiden and what we put into a paper was expanded out to three lectures by the Leiden people. I think we were there something like a month and two or three days a week Oort would call us in and we'd just sit down and have a two or three hour discussion, maybe Oort and van de Hulst, and Westerhout and I. I mean Oort was a great seeker after the truth.

Sullivan

Well, so long as he liked the idea of your truth. You visited Jodrell Bank, I guess?

Bolton

Yes, I spent quite a lot of time at Jodrell Bank. In fact, one of the things I was given was the Hanbury Brown- [Richard Quentin] Twiss notebook on the amplitude correlation interferometer, to look through it and see if I could find mistakes in the mathematics. In those days it was terribly complex and you just got lost in the mathematics and you had no physical insight, and all I could do was just plod through it and say, "Well, I can't find any mistakes, but I don't understand how it works." Later that year I went back to Jodrell Bank and of course, they'd done the solar angular diameter by using two overlapping antennas. And I saw Hey at that stage, who was still in Surrey.

Sullivan

Was the 218 foot hole-in-the-ground [Sullivan: actually, 218 foot dish is entirely above ground] built when you were there?

Bolton

Yes. It was there.

Sullivan

This must have made some impression, obviously...

Bolton

Yes.

Sullivan

In terms of later building one yourself?

Bolton

And then I went to Canada where I saw [Arthur E.] Covington’s work, and then to Toronto and Cornell and Harvard and Yerkes Observatory, which was solely optical.

Sullivan

At Harvard you saw for yourself Ewen and Purcell working on [Sullivan: 21 cm line]- this was 1950 now. So this was the year before it was detected.

Bolton

Yes. Well, of course, I'd seen the Dutch work going on with the receiver and it, of course, destroyed in the fire, they should have won, but the fire destroyed the initial receiver. And then I traveled across the country and spent quite a lot of time in Pasadena and finally Berkeley.

Sullivan

Where...

Bolton

And, of course, I lectured in all these places. Many people said afterwards, "You know, the thing that really changed history with your visit to Copenhagen and Götenberg."

Sullivan

And in what sense?

Bolton

In the sense that radio astronomy became a reality to them.

Sullivan

I see. Places that hadn't had the contact.

Bolton

Places that hadn't had the contact- actually met people with slides and records and ideas and that kind of thing. You see, radio astronomers didn't get around.

Sullivan

They didn't go to optical observatories.

Bolton

I was the first person.

Sullivan

Which is perhaps having to do with your reading twenty years of ApJ and so forth. You obviously had more of an orientation this way.

Bolton

Yes.

Sullivan

In fact, a question I want to ask you: in the late ‘40s if someone asked you, "What do you do?" at a cocktail party or something, what did you say?

Bolton

By 1949 I was saying, "I'm a radio astronomer." I think I was the first person to use those words. In fact, I gave a lecture at the Royal Society of New South Wales and the title was "Radio Astronomy" and this was the first time I'd used it myself.

Sullivan

And before that you'd have said what?

Bolton

Before that, nobody asked me. I mean, I worked out on Dover Heights and it was very difficult to say what I was doing and I had some contact with Mt. Stromlo, particularly Clair Allen.

Sullivan

I talked to him a couple of days ago. But indeed, that's very early for someone to be calling himself a radio astronomer. I don't think I've had anyone else say...

Bolton

Well, I made radio astronomy the title of this lecture, you see.

Sullivan

But it seems to me there was a discipline called radio astronomy starting in 1948 or '49 and everyone sort of understood this, but people did not call themselves radio astronomers until really, the late 50's in general. They were always thinking of themselves as radio physicists or engineers or physicists.

Bolton

Oh, no, I was appointed Professor of Radio Astronomy at Caltech. It was the Radio Astronomy Department right from the beginning.

Sullivan

That's '55.

Bolton

You said the late ‘50s.

Sullivan

Okay, mid- ‘50s. And Ryle also got a chair in Radio Astronomy in 1958 or so, and I guess Lovell a little bit earlier.

Bolton

I think the Manchester people always considered themselves radio astronomers.

Sullivan

I may not have asked that question of Lovell.

Bolton

They called those things "telescopes".

Sullivan

Yes, that's true. And I know Lovell does have an article in 1948 or so where he talks about radio astronomy. Another general question - over the years and especially up to the Parkes dish, what, in your opinion, are the key ingredients to the success that Radiophysics has had in terms of being one of the three or four leading places?

End of Tape 101B

Sullivan Tape 102A

Sullivan

To what do you attribute the success Radiophysics over the years?

Bolton

Well, we did get in on the beginning, which is an important step. There was very little point in coming in second, which meant that we could do things with pretty simple equipment in the early days. We had the advantage of weather, winter or summer one could work outside here. If you're in the Soviet Union, you can only lay concrete during three months of the year and that kind of thing. And there are the same difficulties in North America, even in Britain. So the weather was on our side. And I think Taffy Bowen was on our side.

Sullivan

In terms of constantly supporting the effort?

Bolton

In terms of letting people have their head, I think. Giving you a pat on the back when you did well and commiserating with you when something failed. I think he had an attitude which helped things along. And the other thing, of course, was the complete openness at Radiophysics; people talked to each other about what they were doing and so on, which didn't happen in a place like Cambridge.

Sullivan

Even amongst the sub-groups at Cambridge, you're saying?

Bolton

Yes.

Sullivan

I’ve gotten the impression that, while there may have been openness, there was a lot of isolation because of all these field sites and so forth.

Bolton

Well, you asked for the very early days.

Sullivan

Well, no, I'm asking over the whole period.

Bolton

Over the whole period. Well, I think one of the things is that there was enough of us, and so generally somebody was on top. This was important, say, in the middle phase, around 1950-55. Where you can have three or four groups who are building equipment for a couple of years, but one of them had got stuff coming out and so on. And so from the outside it looked as though Radiophysics was...

Sullivan

A lot of depth in other words.

Bolton

Yes. There was a lot of depth.

Sullivan

You did not work here during the war. Most other people have commented on the outgrowth of the laboratory during the war, and how this set the style for rapid innovation and these sorts of things. But that's not part of your background.

Bolton

No.

Sullivan

You didn't observe this to be an important influence though?

Bolton

Radiophysics has not always been successful. I mean, I think, at all stages someone must have been very irritated with the lack of progress that, when you compare...

Sullivan

Well, yes.

Bolton

I mean, that's why the Germans lost the war, we were bloody inefficient, but they were even less efficient, you see. There are only really a couple of places in the world that I've visited which have something of the same spirit as Radiophysics. One is Bell Telephone Labs and the other is Lick Observatory. Lick Observatory over the years, as you know, has been much more successful than its massive counterpart a few hundred miles south. Bell Telephone Lab was always a very good organization; well, it's not such a good organization now, it used to be in a lot of little huts with duckboards between for bad weather and that kind of thing, the director took his turn each week in cutting up on day a week, and so on. But there, individuals were allowed to operate as individuals.

Sullivan

So you think that's a key element in any...

Bolton

Yes, I think that's a key element. Of course, how one integrates it into a large machine like we've got now... there were stages when this was pretty difficult, but we now very much are back to operating on an individual basis. Parkes is set up so that the observatory is virtually autonomous.

Sullivan

What do you mean by that?

Bolton

Well, it runs itself. Radiophysics doesn't run it.

Sullivan

I still don't see what you mean. What would be the alternative to that? You've got to have somebody who selects who gets what time and what the overall...

Bolton

Well, this is done by a committee, who gets what time.

Sullivan

By autonomous, do you mean democratically run rather than in an authoritarian fashion?

Bolton

Yes, I mean, the local staff here operate the telescope without interference from, there's not a great deal of interaction between...

Sullivan

From Sydney, yes.

Bolton

From Sydney, I mean, Radiophysics is just one of the organizations which uses this telescope.

Sullivan

In fact, that's true now, yes.

Bolton

Yes, it wasn't so true in the early days, but in the early days we didn't have the support facilities here. There was me and John Shimmins, one mechanic, and one electrician and that was it. So people had to do the things that a telescope was capable of doing; nowadays, of course, it's equipped with receivers which span the entire spectrum, off- and on-line processing equipment and everything like that, so if a program's feasible at all, you can get it on the Parkes telescope whether you know anything about radio astronomy or not... About one quarter of our observers now come from optical observatories. You know, the U. K. Schmidt people, the Anglo-Australian people, the British visitors that come out to the A.T. and so on, they all get on the Parkes telescope. So there are really lots of individuals using the telescope once more. This wasn't true in the early days, when the scientists very largely- you couldn't use the 21 cm parametric amplifier unless you worked with the man who built the 21 cm amplifier.

Sullivan

And you knew how to tune it and where the liquid nitrogen was?

Bolton

That was Frank Gardner, and what's more you couldn't operate unless you worked for somebody who knew how to drive the telescope.

Sullivan

I think this has been a fundamental change in the science which took place in the mid ‘60s somewhere.

Bolton

We have evolved to this state, although people still can't get their observations done for them as they do at Green Bank.

Sullivan

Or Westerbork, of course, is the ultimate in this.

Bolton

Westerbork is the ultimate in this.

Sullivan

But don't you think this was inevitable? There are very few places where this is not the style of operation now, because of the extreme complexity of the instruments.

Bolton

You have to have the support. But still, the people who are capable of building their own equipment and their own telescope do a lot better.

Sullivan

It certainly is a plus for them, but it's not a necessary thing.

Bolton

No, it's not a necessary thing.

Sullivan

Well, is there anything else that you would like to comment on the overall history of radio astronomy up through the early ‘60s?

Bolton

I don't think so, really.

Sullivan

We really haven't commented specifically on the whole log N - log S business and what radio sources are telling us about cosmology. Let's just end with that. Starting with your attitude in the '50s, it seems like it was clear to you that these Cambridge sources were not real- what about the Mills survey? Did you feel like that was giving you more reliable...

Bolton

Yes, certainly more reliable because it was a synthesized pencil beam, which is one stage better than the confused interferometer stage.

Sullivan

But you're implying still not as good as a filled aperture?

Bolton

Oh, no. Nothing can beat the filled aperture. But I mean the whole log N - log S business is pretty well sorted out now, everybody is in agreement as to what the log N - log S does, it goes up very slightly steeper than -1.5 and comes down and eventually turns over, and depending on what frequency you're using, those effects are magnified or diminished to some extent.

Sullivan

But, of course, what has changed greatly is the general attitude toward its applicability to telling us something about the nature of the universe.

Bolton

Well, as far as the nature of the universe is concerned, it all depends on what you want to believe in. If you are looking for something that parallels the birth and death of a human being, then you're going to find the birth and death of the universe. But that's not necessarily so- it's very difficult to get away from this attitude.

Sullivan

In our western culture anyway.

Bolton

It’s the circumstances of one's environment. One lives in a bio-chemical, irreversible-process world, and so on the large-scale physics of the universe, it's hard not to inflict your personal life history on that of the universe but I don’t think that is necessarily the way. Fritz Zwicky used to say, "You must look at the universe for what it has to tell you, not for what you want to find, because you'll always find what you want."

Sullivan

Right, but of course, that's extremely difficult to do.

Bolton

Yes, it is difficult to do.

Sullivan

Sounds like you're a bit of an agnostic as far as cosmology goes.

Bolton

Yes, because one is constantly, forcibly struck by... When I grew up in astronomy, the universe was a quiescent universe in which all the energy in the universe was represented in the thermonuclear processes which took place in the inside of stars. Apart from certain cataclysmic events, 1010 years was the sort of time scale on which things changed. Now the universe has taken an awful beating since those days. Things change in milliseconds. And the energy in the universe is by no means confined to the thermonuclear processes in stars. I mean, physics is a reversible thing, not an irreversible thing. sure, in most cases radiation is down-graded, but then there are things like masers in which radiation is not being down-graded and I don't think that we're, by any means, at the end of these things. So I think it's very naive to look for births and deaths in the counts of radio sources. One of the curious things is that one doesn’t find as much "birth and death effect" in the objects which are very much more distant, the flat-spectrum quasars and so on show nothing like the steep log N - log S that the radio galaxies do. Now this is very peculiar, you see, because you’re looking back a lot further.

Sullivan

Yes.

Bolton

And I have a sort of vague integral theory, that all one has to do is just expand the universe and these things all happen naturally. I think the key to this is perhaps the relationship between interstellar and intergalactic densities, perhaps in the very early universe. I mean just taking something which is expanding, intergalactic densities were at one time on of the order of interstellar densities, and so the confinement of the radio source is almost assured.

Sullivan

Yes.

Bolton

Then as the universe expands, the galaxies don’t scale, but the intergalactic material does scale, so you're left with a changing ratio of interstellar to intergalactic densities. What this means is that you now come upon two classes of objects, one in which the interstellar densities are high enough to confine a radio source, and one in which the interstellar densities are not high enough to confine a radio source and once it is out in intergalactic space there is nothing to confine it. And out of this one can put quite a nice scenario that, say looking back to redshift of 3 or something like that, everything is in the form where the interstellar density and the intergalactic densities are of the same order, and one has confinement and only small-diameter sources. As we get down to redshift of .5 or something like that, one gets to the stage where elliptical and spiral galaxies are very different, and in the case of the spiral galaxy arm still has the interstellar density to confine the source. But in the elliptical galaxy, it’s gone down, and one produces the epoch of large-diameter, high-luminosity sources. The last three graduate students I’ve had, for example, even though I have the attitude it doesn’t necessarily say anything about the birth and death of the universe, they all ended up with the same thing. [Jet Merkelijn’s?] thesis, which was on the luminosity of high-redshift radio galaxies, simply says that if one interprets the redshift as cosmological, then some rather drastic evolution is required for radio galaxies. Jasper Wall on quasars came with the same thing. Now Ann Savage has come up with the same thing- even more so- on optical QSOs.

Sullivan

But there seems to be a little bit of a contradiction, because you at first made the philosophical point that the answer you get depends on the question you ask. And yet you were saying that in the past thirty years you were saying the universe has taken a real beating because of what's been observed - fast time changes, very energetic processes, and so forth. Are you then saying that these things have been observed because these are only the things that we've looked for? You see what I'm getting at?

Bolton

Well, theorizing is always based on the belief that we know everything.

Sullivan

I don’t follow that. You mean you know everything that's of importance for the problem at hand?

Bolton

Yes.

Sullivan

Something could be discovered tomorrow which...

Bolton

Yes. If one had some down-conversion process which affects the transmission of radiation, this would get rid of the strange paradox of the flat-spectrum sources not having a steep log N - log S. The only real relation to anything I can find is the spectral index of the object, the steeper the log N - log S curve. And that’s something which really nobody has explained. It may be just that spectral index is an indicator of angular size, brightness temperature, or this idea of the non-scaling intergalactic medium- that kind of explanation, but there may be some other explanation.

Sullivan

So in terms of pre-1960, I would think that you would say that this was not premature to be making cosmological implications based on source counts if you had some reasonably reliable source counts and this process is still going on today.

Bolton

Yes, it's perhaps unfortunate that the issue was clouded for so many years by inadequate experimental data which gave you very much exaggerated slopes.

Sullivan

But the principles were okay if the right data had been put in? Or some more adequate data?

Bolton

Not necessarily, no. No, as I said, a down-conversion process would operate just as well.

Sullivan

Okay.

Bolton

I mean we're going back to the assumption that we know everything... Why I brought up the changes in what we know about the universe is that it's quite clear, even with the progress we’ve made in the last thirty years, that we don't know everything, and there may be other factors. One is still up against quite a lot of difficulties I think, in the energy-generation processes for some of these objects on the assumption of any reasonable lifetime. You can say we can invent some new physics to explain the generation or invent some new physics to explain the energy generation or invent some new physics to explain the redshift. Nobody can think of the other ways of getting the redshift- that appears to be the most difficult, so we leave the energy generation to the unknown...

Sullivan

Okay, well, thank you very much. That ends the long interview with John Bolton on 15 March ’78 at Parkes.

Citation

Papers of Woodruff T. Sullivan III, “Interview with John G. Bolton, 15 March 1978,” NRAO Archives, accessed January 17, 2021, https://www.nrao.edu/archives/items/show/903.