Interview with John G. Bolton, 13 August 1976
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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.
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Sullivan
So this is talking with John Bolton at Jodrell Bank on 13 August ’76. Could you tell me a little bit about your educational background and then how you got into radio work?
Bolton
Yes, I was born in Sheffield and I went to the grammar school in Sheffield and then I did a physics degree at Trinity College, Cambridge. That was in the beginning of the War.
Sullivan
Graduating in what year?
Bolton
'42. From there I went into the Navy as a Scientific Officer and worked on airborne radar and finally in the last year of the War, I was in the Pacific with the Pacific Fleet. I was on a base carrier there, more or less dealing with all problems in electronics. And I stayed in Australia after the War.
Sullivan
But this was the Royal Navy?
Bolton
This was the Royal Navy, yes. And I joined the Radiophysics Laboratory.
Sullivan
Now I think it you and someone else that answered similar advertisements. Is this the right story? You and [John] Paul Wild?
Bolton
Oh, Paul Wild, yes.
Sullivan
Can you tell me that?
Bolton
Well, I was in Australia. Paul was also in the Pacific Fleet. He was a radar officer on the King George V battleship. When I got out of the Navy, I really had no intention of doing any work for some months. The British Navy transferred me to the Australian Navy and I went through Australian demobilization. And one of the questions on the form I had to fill in said, "Do you want assistance with employment?" So just for the fun of it I put a tick in that column. I saw a man an hour later who was looking for bricklayers and painters and he said, "I'm not really the right man to see," and he gave me the name of the man who was then Director of Higher Appointments in New South Wales. I went to see him that afternoon and he rang up the University’s Commission and they put me in touch with [E. G.] "Taffy" Bowen, of course, who had been at TRE [Telecommunications Research Establishment] in England, one of the early people at TRE.
Sullivan
Right, I have talked to him.
Bolton
Yes, I went and saw Taffy and he offered me a job, you see. So being in public service, they had to advertise a vacancy and at that time Australian vacancies in scientific fields were advertised world-wide and Paul saw the advertisement in Nature and applied for it. I remember Taffy coming into the room where I was working and after I'd started work, he said, "You wouldn't happen to know this man, would you?" And I said, "No," and asked a little about his background. Paul was at Cambridge at the same time, but we were a year different and in different colleges- "He must be a good type." So Paul was offered a job. About 10 years later we were virtually running the Labs.
Sullivan
So you also mentioned to me that you and Paul were both born in Sheffield.
Bolton
Yes, within a few hundred yards of each other, but his parents left Sheffield when he was quite small. Of course, mine remained in Sheffield.
Sullivan
Was Paul offered a job in answer to that advertisement?
Bolton
Oh yes. Two positions were made.
Sullivan
And when you took this job, what did you think you were getting into, or did you just know that it was something to do with radio?
Bolton
Well, at the time Taffy Bowen was really only interested in the Sun and I, in fact, started working on the Sun. I built equipment to determine polarization of solar bursts. D. F. Martyn, who was a brilliant ionospheric physicist at Mount Stromlo [Observatory], had done some theoretical work and it was suggested that we might work together.
Sullivan
So you knew definitely that you were getting into radio astronomy, or was it called that then?
Bolton
No, it wasn't called that. That was called "solar noise." The equipment we built- we had an old radar experimental station on the cliff edge on the south arm of Sydney Harbor and made our observations from there. And to a certain extent, rather than work on the Sun, which seemed pretty dull. Stanley and I attempted to break up the background of the galactic noise into discrete sources by utilizing the sea interferometer.
Sullivan
Now, knowing about [James] Hey's discovery of this one source, you said that the galactic background might be composed of many more of these. Is that the idea?
Bolton
Yes, essentially Hey's work was rather independent. Hey's work was published while we were working on the Sun, and [Joseph L.] Pawsey had made an attempt to detect the scintillations which Hey saw- the fluctuations in the Cygnus source- but actually didn't get any results. He couldn't duplicate Hey's work. Our work to a large extent was quite independent of Hey's. We started a systematic search pointing a relatively low-directional antenna over the sea and just recording what came in the background galactic noise and looking for signs of interference patterns.
Sullivan
Why do you think that Pawsey did not get scintillations? Was it because of a much higher zenith angle?
Bolton
Well, I really don't know because I didn't see Pawsey's records. But, of course, the source might well not have been scintillating when he looked at it. As it happened, NGC 5128, the Centaurus source, and the Cygnus source were really discovered on the same night. The Centaurus source we’d found before the Cygnus source, but our signal-to-noise ratio was so poor at the time that the observations were practically of no value. And as soon as we got the stronger one- we spent some months following it up, trying to locate the position and everything that before we went back to the routine survey. In fact, in our historical list the Crab Nebula is shown as the second that we'd discovered.
Sullivan
I'm a little confused. Did you know about Hey's discovery of a discrete source?
Bolton
Yes, we knew about Hey’s discovery of a discrete source.
Sullivan
Before you found Cygnus with your instrument?
Bolton
Yes. When we found Cygnus, we related it to Hey's discovery.
Sullivan
I see what you're saying, Ok.
Bolton
As far as we were concerned...
Sullivan
You weren’t certain that it really was a discrete thing?
Bolton
Pawsey had got a negative result on trying to repeat Hey's observations.
Sullivan
I see. Very interesting.
Bolton
As far as I'm concerned, Hey gets the credit for discovering discrete sources.
Sullivan
Yeah.
Bolton
Historically it was the first indication.
Sullivan
Right.
Bolton
But our work on Cygnus was really quite independent of Hey, and, as I say, it followed a negative by Pawsey.
Sullivan
Right. Which was never, published- this negative result?
Bolton
Which was never published, no. Now, as we later learned in our spaced-aerial experiments, the scintillations were scintillations and not real fluctuations of the source. And particularly with [O. Bruce] Slee, I did a lot of work on the diurnal and annual variation of these things and it's quite conceivable that at the time Pawsey made his observations the source was, in fact, not scintillating.
Sullivan
Before we go on anymore with your sky survey for sources, let me go back to this business about the Sun. You said your goal was to measure polarization, in the solar bursts, I gather. And there was indeed, within a couple of weeks in Nature, three different groups reporting polarization, [Martin] Ryle and [Derek D.] Vonberg, [Edward] Appleton and Hey, and the Australian group - I can't quite remember who the authors were [WS: Martyn]. I don't think you were one of them though.
Bolton
No. We, in fact - Stanley and I - did very little work on the Sun. We did though get the first of the Type II outbursts. And this was published under [Ruby] Payne-Scott, [Donald E.] Yabsley, and Bolton. Ruby and Don Yabsley had been working on trying to measure a time difference between different frequencies for what we now know as Type III bursts. And Stanley and I had a very happy accident in seeing the first of the Type II outbursts with a very long delay to us between our various frequencies.
Sullivan
And that was what was mentioned here in the summary of that article, that some time delays as much as a few minutes are seen.
Bolton
Yes, that's right. And that, of course, indirectly led to the spectrograph on which Wild started.
Sullivan
Right. But he wasn't working in that group at that time?
Bolton
No, he was actually working in the test room of Radiophysics. Testing electronics.
Sullivan
Well, I'll have to talk with him about that because he doesn't surface in terms of publications until '50 or so.
Bolton
No, well they spent a long time building the spectrograph.
Sullivan
Which paid off, of course.
Bolton
Which paid off.
Sullivan
Ok. So you joined CSIRO in '46 then?
Bolton
Yeah, it would be around August or September '46.
Sullivan
And spent some time then working on the solar work, but then decided that it would be more interesting to look at these discrete sources. And you say that Centaurus and Cygnus were the first ones that...
Bolton
A very poor record of Centaurus and a moderately good record of Cygnus were in fact obtained on the followed same night. The Crab followed about three months later.
Sullivan
This was using the sea-cliff interferometer technique?
Bolton
Yes.
Sullivan
Let me ask about that. It's my impression that this was a direct outgrowth of techniques of radar that had been used onboard ships, is this correct?
Bolton
Yes. Well, ships and shore base.
Sullivan
And were any of the people that got involved in radio astronomy later involved in this development during the War?
Bolton
At one stage during the War, I operated a night fighter, squadron on the Chain Home Low station on the Firth of Forth. And, of course, the sea interference pattern was a nuisance to us.
Sullivan
So you knew about it from practical experience?
Bolton
Yes, on board ship experience- the sea interferometer was nothing new. In fact, we had a short training burst at Portsmouth before we went out into the service. There is a Canadian radio astronomer Carman Costain; well, his older brother [?] Costain, who was at the Hertzberg Lab and I were on the same course at Portsmouth. We designed an analogue computer to determine the height of an aircraft using the sea interferometer. Timing the intervals between passage through successive lobes.
Sullivan
But were any of the other people, like Pawsey or Bowen, involved in the development of the sea interferometer as a military technique and then they just said, "Well, let’s just take this over?"
Bolton
No. It was a well-known phenomenon.
Sullivan
I see.
Bolton
I mean, we happened to utilize it in Australia because...
Sullivan
That's the next question...
Bolton
We had some cliffs. I mean if we had been at Blackpool or something like that, well we probably wouldn't have done it.
Sullivan
And you used it also, I suppose, because of its advantages- namely you only need one receiver and you don't have to worry about phases...
Bolton
Yes. It has a nice gain in sensitivity for a small antenna. You don't have to divide signals between impedances and so on, so you get four times the gain at the antenna, effectively.
Sullivan
Right. And the procedures for correction for refraction and sea state, and all these sort of things- were you able to take those over directly from available literature or did you have to develop new...
Bolton
No, refraction was one of our problems in attempting to locate the source. What we did determine was the times of the minima of the pattern. And from the geometry, wavelength height above the sea, and so on you could compute the actual answer. And then you had to know the refraction, and this was really a problem. You could get a reasonably accurate time of crossing at the horizon, but then to get another coordinate was very difficult because it was not just the refraction, it was the differential refraction between a relatively small series of fringes. Although we did publish the position of Cygnus quite early on in the piece, I wanted to go to New Zealand. Well, we had the choice of going to New Zealand or going to Perth to get a west coast, where I'd reasoned it was possible both to solve the refraction problem and solve the source position. And New Zealand was closer than going to Perth, so we set off for New Zealand. I remember Taffy asking me what I really thought of the positions of my sources and I said, "Well, they’re the best I can do at the moment, but I'd like to be the first to correct them." And indeed the corrections were absolutely massive when they came in. And one of these things resulted from the fact that we'd taken a combined ionospheric refraction correction, which had been worked out on the wrong theory by Pearcey. This relied for its experimental data on some of Pawsey and Payne-Scott's observations of the Sun. And it was hopelessly in error, and our early radio source positions used these corrections which were hopelessly in error. The reason why they were hopelessly in error was not realized for several years in that the optical positions of sunspots had been adopted as the radio positions of the sunspots. And all the spots which had been studied were on one limb of the Sun...
Sullivan
Yes, and so the radio burst was way off.
Bolton
The radio bursts, of course, being way off gave a totally false low angle refraction correction. And, of course, as soon as we got to New Zealand, we first made observations from the east coast and at a not being at much too different a latitude, the times of rising of the source were fairly well in accord with what we expected. But of course once we got to the west coast, real big errors were found and we started looking for sources half an hour after they'd set. That's the other thing we found from New Zealand, that the Earth was curved.
Sullivan
Now why did the west coast help you in the refraction problem?
Bolton
What we had was a line on the horizon which corresponded of to the time of rising of the source. Now, don't forget, we're working at very low frequencies, and the atmosphere and the ionosphere behaved extremely irregularly, and so the times of minima of sources could scatter by as much as 5 minutes on an individual night. By taking a lot of observations you could get down to, say, an error of one minute. So you had a band along the horizon which might have been a quarter of a degree wide. Now, where you put it in azimuth on the horizon depended upon the timing to successive altitudes. And if your refraction curve was way out, then it put the declination way out. However, by going to a west coast you had a time of setting, which was only within one minute. And this gave you, without any further corrections, an error box which was only .25° in extent. And then knowing the approximate declination from that- or a pretty good approximation of the declination- you could go back and say what the form of the refraction curve had to be. It put certain limits on its form and therefore tightened up this one minute time of rising. You couldn't have something absolutely ridiculous in the way of a refraction correction. As it happened, the refraction correction in the mean came out to be just the same as optical. That is, the ionosphere pushed you one way and the other by enormous amounts times. So our stay in New Zealand was just a matter of down the beating down the statistics.
Sullivan
Well, except in [L. L.] McCready, Pawsey and Payne-Scott, their big solar paper, the time of rising of the Sun was well after the first fringes received on the interferometer, which would indicate to me that the refraction was much greater at radio wavelengths than optical.
Bolton
Ah, yes. But the position of the radio sources were very different from the position of the optical sources. That's the point.
Sullivan
I haven't looked into this. So it is true that at the horizon the optical and radio refraction are about the same.
Bolton
Right. But you see, they had all their spots on one side of the Sun.
Sullivan
And in fact it was on the... Let's see, you see the radio before you see the Sun.
Bolton
That's right.
Sullivan
So it's on the high side.
Bolton
On the high side of the Sun. You see, that was the thing which threw us. Now, of course, a couple of years later when Payne-Scott and Little started doing positions of radio emission from spots, of course, this was very obvious.
Sullivan
Right. Ok, now let me get the sequence right. Having published these six sources, all of which turned out to be...
Bolton
In the wrong constellation.
Sullivan
Only a couple of them were in the wrong constellation, notably Virgo A moved into Coma Berenices.
Bolton
Yeah, well you'll notice that it depends critically on the declination.
Sullivan
But they all turned out to be real sources, though. Is that not right?
Bolton
[Affirmative]
Sullivan
Two of them you didn't give names to, but they were Hydra A and IC 443, as I've got it here.
Bolton
Yeah.
Sullivan
And they were off by 5° to 10° because of this error thing. But nevertheless that was a big step forward from the one thing that Hey had. Then after publishing this, you decided well, you've got to get these done right and you went to New Zealand to fix a it up and then you... was it also as a result of those observations that you came out with a very accurate position for Cygnus A?
Bolton
Well, we came out with a very good position for the Crab. We still didn't get a good position for Cygnus. I think we were still off by several minutes of arc. But at least we weren't degrees.
Sullivan
In the publishing the Crab comes later but you're saying in actuality you had a good Crab position earlier than you had a good Cygnus.
Bolton
In the publishing, order was I think the identification of the Crab, M87, and NGC 5128.
Sullivan
Right, July '49.
Bolton
Yes.
Sullivan
But the Cygnus position to seven arc minutes was February '48.
Bolton
That was before we went to New Zealand.
Sullivan
I see.
Bolton
And that position, I think, is not very good, and if you look at it carefully you'll find the declination is a degree out.
Sullivan
I don’t have my table there. You probably know the positions by heart.
Bolton
Yeah, I think they are a long way out.
Sullivan
That's right, it's coming back to me now. The importance of this paper is that you got the angular size to be less than something like 10 arc minutes.
Bolton
Yes. That position is quite a long way out.
Sullivan
That's the point.
Bolton
In fact, we never did publish our New Zealand position of Cygnus because by that time we were sort of talking backwards and forwards to Ryle. Cygnus was a difficult object, it never got far above the horizon and so on. But our next significant step was the identification of the Crab and the two radio galaxies.
Sullivan
Ok, before we get on to that, you brought up an interesting point, namely what did you know about what was going on at Cambridge and/or Jodrell Bank?
Bolton
Pawsey went to Cambridge with essentially the results of our first paper on Cygnus and told Ryle at the time. Ryle left his solar interferometer running overnight.
Sullivan
I see.
Bolton
And, of course, immediately got Cygnus and Cassiopeia.
Sullivan
Right. And, of course, Cassiopeia you couldn't get because it was too far north.
Bolton
No.
Sullivan
And so you think that was really a strong motivation that shifted Ryle from his earlier solar work to radio sources?
Bolton
Yeah, that was the motivation.
Sullivan
In general, though, there was correspondence going on as to what was happening?
Bolton
Yes. Ryle and I had a fairly complete exchange of letters. We had our problems with the sea interferometer and he had his problems with the east-west interferometer, and so on.
Sullivan
Since you brought that point up, the direct comparison, you stuck with the sea interferometer till early ‘50s, is that correct?
Bolton
[Affirmative]
Sullivan
What was it, do you think, that eventually laid the sea interferometer to rest as a useful astronomical instrument?
Bolton
Well, around about ‘51, we tried variants of the sea interferometer, two antennas as a cross north-south interferometer, crossing an azimuth interferometer with a sea interferometer.
Sullivan
Two antennas on the same cliff?
Bolton
Yes, on the same cliff- mainly to get rid of the large background. Stanley and I decided we couldn't get any further without...
[Interruption]
Bolton
We built an 80 foot semi-steerable hole-in-the-ground-type instrument to investigate working at much higher frequencies, where we could be away from the effects of ionospheric scintillations and refraction effects. And Stanley had spent about a year developing equipment for 400 MHz, where we reckoned there would be absolutely no problem this way.
Sullivan
What year is this roughly?
Bolton
Oh, that would be '51. Well, our problems with the sea interferometer- (a) we wanted a much bigger instrument because many of the sources were obviously confused, and second we wanted to get to higher frequencies. So we built this test antenna. It was the one, incidentally, which decided that the galactic center is the galactic center.
Sullivan
Oh, yes, that's right.
Bolton
[Richard X.] McGee and I. And we had a proposal in to build a standing paraboloid, somewhat like [John D.] Kraus' system, fed by dipole stack, in which we could move the position of the dipole across the focal plane to steer the beam. The beam would have been about 4° in the vertical plane by 1° in the horizontal plane. And then we would take the whole structure down, and turn it to another 10°. We had done tests to show the system would work, but at the same time Bernie [Bernard Y.] Mills came up with the idea of the Cross. Taffy Bowen was sort of backing me and [Gordon J.] Stanley, and Pawsey was backing Mills. Pawsey was the head of the Radio Astronomy group and so we lost out and so our next work was in cloud physics.
Sullivan
This was about '52?
Bolton
Yes.
Sullivan
Well, maybe this would be a good place to end. We can resume some time, but I do have a couple of other questions about your identifications. Could you just tell me how that happened? So you have these 6 sources, you got positions which were accurate to ± typically 8 to 10 arc minutes or so.
Bolton
(affirmative)
Sullivan
And then what did you do?
Bolton
The results of the New Zealand observations took me something like three months to reduce manually- terribly laborious. We were at the end of a long power line in New Zealand, and the end of a very long cable on that power line. In fact, lights used to go out at times. The clocks ran fast and slow, you know, just correcting the timing of the records and everything like that- a tremendously laborious business. But by the end of three months, I'd concentrated on the Crab because we had the best records from both east and west coasts.
Sullivan
And you concentrated on Taurus A, didn't you?
Bolton
I concentrated on Taurus A, yes. And, of course, at the end we came out with something that was around 6 minutes of arc. There was an error circle about 6 minutes of arc. And sitting in that was the Crab Nebula.
Sullivan
How did you do it? Just look at a book for the position of the Crab or did you actually collaborate with someone with a photograph?
Bolton
Norton's Star Atlas.
Sullivan
I see.
Bolton
And then I rang up Harley Wood at the Sydney Observatory and said, "Harley, what can you tell me about the Crab?" Well, during long nights of observing, 18 months from Dover Heights, I'd read a great deal of Astronomical Journal, Ap. J., Monthly Notices, and so on. I learned a lot of astronomy. I think [Rudolph] Minkowski had just published a paper on the Crab. Although I hadn't read that, Harley pointed it out to me. A few days later, I wrote to Minkowski and that started a long and valuable collaboration.
Sullivan
I see, yes indeed.
Bolton
I also wrote to Jan Oort and I pointed out these identifications, NGC 5128 and M87 in the Virgo cluster. I had a very enthusiastic four-page letter back from Oort, of which 3.9 pages were devoted to what he knew about the Crab Nebula. And then he made a remark at the end of it, "Of course there are a lot of galaxies in the Virgo cluster." But Oort took that up, although he dismissed it. As you know, he had my old position for this source which was 10° away; when he went to Palomar that summer, he got the plates which showed the jet in M87. So he followed it up, although he dismissed it at first.
Sullivan
When would that letter to Oort be? Because, in fact, I'm going to be looking through the Leiden archives, and Oort really kept his letters in order so I could probably find it.
Bolton
Well, it could be some time around October to December of 1948. Maybe two months more, I can't remember.
Sullivan
I'm still curious, did you ever actually look at photographs of this thing, or was it strictly by R.A. [right ascension] and dec listed in books for all these objects?
Bolton
Well, as it happens, just looking at it in Norton's Star Atlas, there's a fair description of the Crab. And I think both M87 (NGC 4486) and Centaurus (NGC 5128) all pointed out as interesting objects in that. Now, in the case of Cygnus, of course, there was nothing listed.
End of Tape 54B
Sullivan Tape 55A
Sullivan
With John Bolton on 13 August ’76. So, talking about these identifications. It appears then that you did not ever really look at photographs of these things and put in error bars like is done now.
Bolton
Oh, no. That's not quite true. In the case of the three identifications, the Crab, M87, [NGC] 5128, we could get that out of existing astronomical literature. In the case of Cygnus, we did go to Mount Stromlo and had direct photographs taken.
Sullivan
Right, in fact you had in one of your papers the first overlay, I think, ever done in radio astronomy.
Bolton
Yes, that’s right.
Sullivan
But now I'm interested that in the article with the three identifications that you are not willing to believe- it seemed to me anyway- that 5128 is probably a galaxy. Before it’s been talked about it being a galaxy, but you say, "It would seem to favor the latter alternative, for the possibility of an unusual object in our own Galaxy seems greater than a large accumulation of such objects at a great distance." Why were you unwilling to think that this was extragalactic?
Bolton
The existing literature was by no means sure. In fact, in that paper I think I quoted a reference from somebody who was claiming that it was a galactic object.
Sullivan
Right, but it seems you had a preference for that. What was making you think...
Bolton
Well, I guess we were very sure of the Crab's identification. The Crab with its extremely exciting history and what had been determined about it. And it was a galactic source. Mind you, we believed in the NGC 4486 identification.
Sullivan
M87?
Bolton
M87. But we just weren't sure whether Centaurus A was one of its kind, or one of the Crab's kind. So I don't think it was a bias against extragalactic objects. It was simply because the nature of 5128 was unknown. It was described, you know, as a pathological specimen.
Sullivan
An accurate description even today. So you were not working out radio luminosities at this time?
Bolton
Oh, gracious no.
Sullivan
And saying, "Oh my God, we can't have this much radio power."
Bolton
I mean, most astronomers didn't even believe there was anything at all in this radio business. This was one of the great things about Minkowski and Oort- that they did recognize it for what it was and gave a great deal of support.
Sullivan
Right. At this time then you really didn't consider yourself an astronomer? What did you consider yourself?
Bolton
I think I gave a lecture in 1950 which was called, "Radio Astronomy"- at least by that date, I considered myself an astronomer.
Sullivan
Well, thank you very much. That ends part one of the interview with John Bolton on 13 August ’76.