NATIONAL RADIO ASTRONOMY OBSERVATORY ARCHIVES

Papers of Woodruff T. Sullivan III: Tapes Series

Interview with John G. Bolton
At Parkes Observatory
March 15, 1978
Interview time: 3 hours, 40 minutes
Transcribed for Sullivan by Pamela M. Jernegan

Note: The interview listed below was either transcribed as part of Sullivan's research for his book, Cosmic Noise: A History or 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.

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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.

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Modified on Tuesday, 05-Feb-2013 13:31:51 EST by Ellen Bouton, Archivist (Questions or feedback)