Interview with Ronald N. Bracewell

Title

Interview with Ronald N. Bracewell

Description

Ronald N. Bracewell, 1921-2007, Interviewed 8 January 1980 at San Francisco. Length of interview: 185 minutes

Creator

Papers of Woodruff T. Sullivan III

Rights

NRAO/AUI/NSF

Type

Oral history interview

Interviewer

Sullivan, Woodruff T., III

Interviewee

Bracewell, Ronald N.

Location

San Francisco, CA

Original Format

Audio cassette tape

Duration

185 minutes

Interview Topics

Radiophysics Lab 1941+; wartime work; observations on first solar work, 1946-1950 at Cavendish under Ratcliffe doing ionospheric work; observations on Ryle's group; 1952 URSI, Pawsey and Bracewell text, 1958 Paris Symposium; Fourier and other mathematical theory for antennas; Berkeley; Stanford 10-cm spectroheliograph (Chris-cross); general remarks on design methods and how to do experiments

Start Date

1980-01-08

Notes

The interview listed below was conducted as part of Sullivan's research for his book, Cosmic Noise: A History of Early Radio Astronomy (Cambridge University Press, 2009) and was transcribed for the NRAO Archives by Sierra Smith in 2014. The transcript was reviewed and edited/corrected by Ellen N. Bouton and Kenneth I. Kellermann. Any notes of correction or clarification added in the 2014 reviewing/editing process have been included in brackets; places where we are uncertain about what was said are indicated with parentheses and a question mark, e.g. (?) or (possible text?). Sullivan's notes about each interview are available on Sullivan's interviewee 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 support from Associated Universities, Inc., which funded transcription of this interview.

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 by Sierra Smith

Begin tape 130B

Sullivan

So this is interviewing Ron Bracewell at the San Francisco AAAS meeting on 8 January 1980. Could you first tell me what your educational background was, and then I know you got started in Radiophysics at a very early time.

Bracewell

Well, I went to Sydney Boy’s High School and then to Sydney University and obtained a Bachelor of Science Degree in mathematics and physics, and then I continued on to get a degree in engineering in the communications option. The last year of that course was 1941 and the Japanese were already in New Guinea and were preparing to land on the Australian mainland. Shells from Japanese submarines had gone over Sydney and a large fleet had been wiped out in Darwin, although at the time that news was censored. So instead of completing the year 1941, the six or seven people in the communications option of electrical engineering were popped into the Army for six months, where I carried tools for a fitter who was repairing engines in personnel carriers. And then we returned to the university for a short period, about three months, and were graduated earlier than normal and sent to Radiophysics Lab. That would be in about September of 1942. [Note added 2014: Radiophysics Laboratory of the Council of Scientific and Industrial Research (CSIR), later Commonwealth Scientific and Industrial Research Organization (CSIRO)]

Sullivan

Which was on the same campus where you were, right?

Bracewell

Yes, the building was planned by John Madsen, who at that time was head of electrical engineering, and the purpose was to bring physicists and electrical engineers together in an environment where there would be the possibility for consulting and recruiting young graduates. So I don’t believe any of us, there were six or seven of us, refused that assignment. We were very obedient in those days. You did what you were told and there didn’t seemed to be any alternative other than enlisting in the Army. So we all appeared in Radiophysics towards the end of 1942. Well, that was my educational background up to that point.

Sullivan

So what did you find at Radiophysics and what kind of things did you work on there?

Bracewell

Well, my first assignment was to build equipment for voice communication at 10 cm wavelength. I had never seen 10 cm equipment and I was provided with a magnetron, the E1210v magnetron, which produced about 10 mW of 10 cm energy and told to voice modulate it. So I built a magnificent bunch of circuitry to do that. And if you connected this to a 6 foot paraboloid, you could communicate for many miles. My supervisor in this project was Brian Cooper, who I’ve had close contact with ever since. And he knew everything about circuitry and I guess that’s really where I picked up such electronic experience as I have. After doing that I had one or two other special jobs. I had to do some high voltage testing that required 5 kV. There was a transformer for this. And I very nearly blew myself up but survived happily. And then I got back onto another microwave problem. There was a tube known as a lighthouse triode, it looked like a lighthouse. And it was operated in a double-concentric circuit, one concentric transmission line inside another, with two annular plungers to tune these cavities. It was very complicated to make and the mechanical stability was not good. So I developed a pair of resonance cavities into which the triode could be plugged. There was no retroflex folding of the resonance cavities. It was just a solid device made out of one short cylinder of metal. That worked very well. That was a sort of technical assignment that I found myself pushed into.

Sullivan

I think [Grote] Reber used these same lighthouse tubes in some of his receivers.

Bracewell

He very probably did. They were convenient and most of them would work. You’d plug them in and they would work. Others wouldn’t.

Sullivan

You mentioned in your talk this morning that people knew about [J. Stanley] Hey’s secret report of 1942 and they knew about [Karl] Jansky’s and Reber’s work pretty generally, I think. Do you remember any instances of someone on just his odd free time trying to detect any extraterrestrial radiation?

Bracewell

The only attempt I recall is the late 1945 effort.

Sullivan

But this is now after the war?

Bracewell

Yes.

Sullivan

And part of published…?

Bracewell

Now just a moment. Attempts were made before then. As a matter of fact, I remember being present as such an attempt in one of the rooms in Radiophysics Lab, but with no antenna worth mentioning, just with a simple antenna.

Sullivan

A dish? A small dish, you mean?

Bracewell

No, with a dipole. And now that I come to think of it, there was another sort of experiment that people used to do with small dishes, in the two or three foot range, which could be found lying around. I remember it being demonstrated that if you took one of these antennas and connected to a sensitive 10 cm receiver, when you pointed it out the window you could get less noise. You see?

Sullivan

Yeah.

Bracewell

Now obviously this is of some astronomical significance, but I didn’t look at it in an astronomical way at that time and I always felt it was very puzzling. I never quite understood why it was. Now I understood that room temperature was room temperature but why the sky shouldn’t reveal room temperature would have required me to understand the transparency of the atmosphere at a particular frequency, something that was beyond my conceptions at the time.

Sullivan

Do you remember who was doing these things? Could it have been anyone?

Bracewell

Well, I have no idea. But the people that could have been doing it would include John (Goodin?), and Ruby Payne-Scott, and, in that same room, Frank Kerr resided. And one or two others, such as [G. Leslie] Les Wirsu and [R.F.] Treharne, whom you would have never have heard of, I imagine.

Sullivan

Yeah. Ok, so we come to the end of the war and the story as you were telling us this morning is that here you had a lot of people without any jobs to go back to and looking for something to do. Can you tell me how that went?

Bracewell

Well, there used to be many informal discussions, people tried to think of things to do with microwaves. We had megawatt transmitters lying around and people knew that you could cook with them. Unfortunately nobody invented a good microwave oven.

Sullivan

No one put the patent on it.

Bracewell

What a wonderful thing to do. And yet we used to cook things in the front of a waveguide and people loved to produce sparks in midair, which would impress visitors. With a little interference pattern, you could create a spark where there would be no spark in the presence of a traveling wave. And, of course, you could light neon tubes freely anywhere. But people didn’t think of collision avoidance radar or microwave ovens or microwave spectroscopy. Perhaps microwave spectroscopy was discussed but it didn’t seem that you could make a living from it. And there used to be two schools of thought: there used to be people who said immediately when the war is over, the bottom will fall out of radar and you should get back into mechanical engineering where people actually manufacture and sell things. And other felt that maybe there were future lines of development. And cloud physics got off to a good start. Now that undoubtedly was brainchild of Taffy Bowen. And he put a lot of effort into that. He had good global concepts of what the future might contain. So he could see himself discovering what went on inside clouds and then turning that information to the benefit of meteorology, for which he knew there was a demand. So he could see right through to the end of that.

I’ll tell you something else that Bowen did to illustrate that kind of attitude. One day I was down in the machine shop and everyone was backing away from their lathes because an experiment was being run in the following way. You may remember that the hero of Alexandria had a propeller that was driven by steam. You let the steam in at the hub and it runs out along the two arms and there is a short right angle bend at the end. I think that was perhaps called an eolipile. If it wasn’t, some related device was. And Bowen had had a thing like that fabricated; a propeller. It was a propeller with hollow blades made of metal with holes at each end coming out of right angles. And he was feeling gasoline into the hub from a carburetor. And this thing really went round. Lighting it was a bit of an exercise. Everyone had to dodge. They thought the thing would fly apart. But it illustrates his mode of thought. The jet engine by that time was understood and he was thinking, “Well, you have to begin with fuel and you have to have a propeller or something. Let’s take a propeller. So why not feed the fuel into the propeller?” And if you ask that question, there’s the answer. So that just illustrates the fact that he certainly had the ability to look ahead and to think in unusual ways. After all, the division had been set up to do Radiophysics and here he was inventing a dangerous kind of airplane engine.

Sullivan

So who were the people who were pushing for radio astronomy and on what basis?

Bracewell

Well, [Joseph S.] Pawsey and Ruby Payne-Scott were clearly the driving figures there. What the division of effort between them might have been, I can’t say. But Pawsey had administrative duties and he had instructed [Lindsey L.] McCready and Ruby Payne-Scott to go and make some observations. So they had done whatever was needed to modify the radar receiver that was attached to that antenna installation, which was a going concern.

Sullivan

At Dover Heights?

Bracewell

At Dover Heights. And was available for test purposes for substituting one component for another. It was not an active military radar. It was a going radar used by the Lab. So he clearly had told McCready, who was a receiver expert, to modify the receiver and he must have discussed the observational procedure with Ruby, who was a general purpose physicist. And then the three of them made the observations together. Pawsey was present during the observations. He was never noticed as having manual dexterity. And from him I discovered the distinction between dexterity and the ability to plan an experiment. There are people who impress you by their experimental ability but we don’t always distinguish between ability to select the right knob and do the right thing with it and to plug the right connector into the right socket and the planning, the intellectual activity that goes into the planning of an experiment. Now Pawsey understood the planning of experiments very well. He understood measurement procedures very well. But he was a little but clumsy with his hands. In fact, you might say conspicuously so and to some extent it may have been a mannerism. But he undoubtedly had in fact carried out a lot of experimental work with his own hands and he directed it quite well. He had the experience and he knew what he wanted done. So he got this thing set up.

Sullivan

Could this have been an early manifestation of what finally killed him, the brain tumor?

Bracewell

I have no idea.

Sullivan

Other people have told me this in a slightly different fashion about putting Pawsey knobs on their equipment so he would twiddle this useless knobs, rather than one that…

Bracewell

Yes, that story was a standard story. That’s right. I think that probably originated with Ruby. She probably had a knob that was connected to nothing and Joe came in and gave it a lot of twiddling. And then she told everyone, “I put it there was he wouldn’t upset the experiment.” Yeah, that’s a funny story.

Sullivan

They started in the fall of ’45 on these solar observations?

Bracewell

Yes.

Sullivan

You were not directly involved with these, however?

Bracewell

I was in the same room with many of the principles for most of that period, I would say. I would see Ruby every day and Pawsey would be up in that room nearly every day too. He’d talk to everyone about what they were doing.

Sullivan

Well your impressions are therefore very interesting to know. Did it seem like they knew exactly what they were doing or was it just a matter of, well, “We’ll look to see what comes next”? For instance, this morning you described that they certainly understood the whole direction finding technique using Lloyd’s mirror and so forth. But in terms of what they might expect in the Sun and what they were after, was there a purpose to it or was it just to find out “Well, let’s see what’s there.”

Bracewell

No, I’m sure there was a purpose to it. It was known that the Sun was emitting radio noise but it was not known whether it came from restricted regions or was general. And I’m quite sure that that was consciously in the minds of Pawsey and Payne Scott. They went out deliberately to find out how this emission was distributed over the Sun. Now, I don’t know this but I would guess that it didn’t occur to them that they might also get the altitude of the emission from the rotation of the Sun. It wouldn’t have surprised me to learn that neither of them knew that the Sun rotated. The level of astronomical knowledge was not high. But since they had to obtain sunspot sketches as part of this project, they very soon discovered that the Sun was rotating. And it was apparent from the beginning that the radio noise in February of ’46 was rotating at a different rate, not much more, maybe 10% more, but noticeably more, and that implied an altitude.

Sullivan

That is was coming from high in the corona.

Bracewell

Yeah, it would be the low corona.

Sullivan

These sunspot sketches, was that a telescope that was set up at Radiophysics?

Bracewell

I don’t remember how those sunspot sketches were obtained. It will be surely in the acknowledgement to the paper.

Sullivan

That may well be.

Bracewell

It just so happens that I have a copy of the report that existed before that paper was written. And I’ve made this copy for you. This is the report itself.

Sullivan

More or less, the preprint of the paper?

Bracewell

Yes, and it may contain differences, in which case it might in itself have interest. For instance, it has no acknowledgement. Now surely the Proc. Roy. Soc. paper will have, this is the appendix, so if we go back a little bit. [Turns pages] Ah yes, [Clabon W.] Cla Allen is the guy who would have made the sunspot sketches because it acknowledges the Commonwealth Observatory Mount Stromlo and the sunspot sketches would have been made personally by Cla Allen.

Sullivan

I did interview him and so I may have just forgotten. I undoubtedly asked him about these things. What about the question of the quiet radiation versus the disturbed, which of course it was not that clear what was going on at that time. Where they just out to find out where the radiation, not really distinguishing between…?

Bracewell

Well, Pawsey was aware at a very early date that [George] Southworth had made a mistake in his calculations.

Sullivan

I’ve found that correspondence actually, where he writes Southworth.

Bracewell

Is that so? How interesting. So he must have known, perhaps not in 1945 but it may be that the intensity of the radiation being received was very strong. Now [Jesse L.] Greenstein mentioned this morning his difficulty in converting statvolts per meter. It would have been statvolts per centimeter, I can assure him of that.

Sullivan

No, it was microvolts per meter.

Bracewell

It was, was it?

Sullivan

It’s in Jansky’s article, yes.

Bracewell

Well, he may have had difficulty dealing with that as an electromagnetic unit, though one might point out that it is the correct unit for field strength, which is voltage divided by length.

Sullivan

Yes but you see, optical astronomers don’t deal with field strength period, only power density.

Bracewell

Well, electromagnetic waves are electromagnetic waves and the strength in electromagnetic waves is measured by its field strength. So I can’t apologize for the difficulty over that. I can understand the discrepancy of c/4p because that is a more difficult problem. But Pawsey probably knew quite early on that the intensities being recorded were just unreasonably greater than could be explained by a 6000 degree blackbody. That calculation is easy to do. He knew the Rayleigh-Jeans formula. I don’t know how he knew it but I know personally that he did know that. That was part of his stock in trade going back…

Sullivan

Well there had been a couple of papers in the early ‘40s, ’41, who is it by now? [R. E.] Burgess going through some of these thermal ideas that are so common now, having to do with antennas and all.

Bracewell

I don’t remember that.

Sullivan

Burgess is ’41, in the Proc. Royal Society.

Bracewell

Is that a fact? Is that R. E. Burgess?

Sullivan

Yes.

Bracewell

I don’t recall that. So the information was around.

Sullivan

Some of these ideas were current.

Bracewell

Well, Pawsey very probably was in contact with Burgess. Probably he knew him. Pawsey knew certain things and other things he knew nothing about whatever. For instance, I had the pleasure of explaining to him what variance was. He had never heard of variance at the time we were working together on our book.

Sullivan

In ’53 or so?

Bracewell

That would be about ’52. He didn’t know variance. Now, that was very strange but he did know an interesting assortment of things in physics. Well, he did know the blackbody radiation.

[Interruption, short break]

Bracewell

As to the distinction between the quiet and disturbed Sun, that distinction became apparent immediately because the observations in October of ’45 showed big disturbance going on but of course they were not persistent. And when they disappeared, you had the residual left over. So the distinction between the two kinds of Sun came in immediately. Now the classification into all other sorts of bursts and whatnot is much later. I think noise storm was a term that was used quite early but disturbed Sun and quiet Sun were terms that came in very soon.

Sullivan

There were several papers in Nature in ’46 trying to straighten this sort of thing out. You mentioned also this morning the famous sentence in Pawsey, McCready, and Payne-Scott paper about the basic Fourier principle. [Note added 2014: McCready, J.L.; Pawsey, J.L.; Payne-Scott, Ruby. Solar Radiation at Radio Frequencies and Its Relation to Sunspots. Proc. Roy. Soc. London A 190, 357, 1947. The paper was submitted as Pawsey, McCready, and Payne-Scott, and is often spoken of that way, but the Royal Society insisted on alphabetical author order]. Now obviously I’m extremely interested in your views on the whole Fourier influence on radio astronomy. Was this generally known by those doing radio astronomy right at the end of the war and first post-war years? Or was this something that only a couple of people understood, do you think?

Bracewell

Well, there were a lot of people in the Radiophysics Lab that understood Fourier transforms and for a very simple reason, that we’d been closely connected with antennas and their radiation patterns. And Pawsey had been working on transmission lines, antennas, and radiation patterns in the period from about 1933 to 1938. So while I would not have said that Pawsey had fluency with things like Fourier transforms, in fact he was a non-mathematical person as regards symbolic manipulation. But there were many people in Radiophysics who were quite at home with Fourier analysis in its mathematical form. I would have been one. Tom Kaiser wrote a chapter in the textbook of radar. Have you seen the book? [A Textbook of radar - a collective work by the staff of the Radiophysics Laboratory, Council for Scientific and Industrial Research, Australia. Angus and Robertson, 1947. Kaiser wrote chapter 7, "Aerials."]

Sullivan

Yes. Yes.

Bracewell

In which, he is explaining that kind of thing. There may even be another chapter in which the Fourier transform is invoked.

Sullivan

Is it fair to say that during the war Fourier transform ideas in terms of antenna theory began to come in because I don’t think that it is very prevalent in the ‘30s from my looking at Proceedings of the IRE and so forth.

Bracewell

During the ‘30s you would have had to read Rayleigh’s papers to be aware of it, either in acoustics or directly in electromagnetic theory.

Sullivan

So it wasn’t being used by the practicing antenna engineers? That’s what I’m getting at.

Bracewell

No. Well the microwaves didn’t exist you see, and with the lower frequencies, directive antennas were not all that common. And the only directive arrays were some large transatlantic arrays of towers, things like half a dozen towers in a straight line. It doesn’t give you very much freedom to control an aperture distribution. But with microwaves you immediately have that possibility. Things like the cosec² antenna which tries to make echo strength independent of angle of elevation gets you straight away into the Fourier transform relationship between antennas and their patterns. The Fourier transform relationship between visibility and an intensity distribution is quite a different physical phenomenon but of course the formula is the same if you so choose the quantities so that it is the same. The thing is we come in historically with a Fourier transform we are familiar with, then of course for economy of thought we will try to formulate our next subject so that it’s the same transform. Then we can use our intuition.

Sullivan

It was really this second Fourier transform I was asking about, the general realization of the relation between the visibility function and what we call the brightness distribution. Now that was even less known than the antenna one.

Bracewell

It wasn’t known at all. The first mention of that must surely be the Pawsey, McCready, Payne Scott paper and the mode of thought by which that originated is quite transparent. If you had a point source on the Sun rising above the horizon, through that cosinusoidal pattern you would get a cosine record. And if there was another point source of a different strength of a different location, it would superimpose another cosine wave on that. So Pawsey saw quite clearly, and for all I know Ruby Payne Scott may also, or they may have discussed this jointly, which they probably did, they saw the superimposition cosine waves would account for your source distribution.

Sullivan

But why hadn’t this come up in the previous work with airplanes? It seems like this would be a useful concept.

Bracewell

Well, they are point sources and all you are trying to do is locate them. Now if you were trying…

End of Tape 130B

Begin Tape 131A

Sullivan

Ok, this is continuing with Ron Bracewell, talking on 8 January 1980. On the Fourier transform a bit more, I’ve talked to many people from the Cambridge group about its influence on their work. They all ascribe a strong influence to [John "Jack"] Ratcliffe’s course on Fourier transforms. Did you take that course or did you see its influence on their work?

Bracewell

Well, yes. Ratcliffe had given this course, a short course of lectures, maybe only as many as five lectures for a number of years running. And I possibly took it about the third go round, maybe just the second time round, but I think it had been given once before anyhow. And after I had been through it, in some subsequent year someone took notes, and then after that the notes began to circulate. I never saw those notes but someone at Manchester, I forget who now, almost published them. And in fact later it was published as a book but with an acknowledgement in it. [Fourier Transforms and Convolutions for the Experimentalist. R.C. Jennison. Pergamon Press, 1961] It very nearly got published without an acknowledgement. The others will have told you that story.

Sullivan

No, I’ve never heard that. There is a book by Ratcliffe?

Bracewell

No, no, no. Ratcliffe never wrote it up, you see.

Sullivan

I see. This guy who took the notes…

Bracewell

But someone took notes and they were reproduced for use of other students. It must have been on a random basis as such things are. And then someone, one of the well-known names only it just doesn’t come back to me at the moment, very nearly published them. And then someone discovered this and then there was a protest of some kind and it was held up. But I think they ultimately were published with a proper acknowledgement. So Ratcliffe did indeed give a half a dozen lectures. Now, I believe he got his knowledge – he was also a non-mathematical person, I should tell you, very noticeably so. That’s not to say that he didn’t know a lot of mathematics, but he did not sit down and solve things mathematically. He thought them out very carefully and once he’d thought it out, he could write it in mathematics. I believe he got his knowledge of Fourier transform from the crystallography group in the Cavendish. There were people in the Cavendish, [William Lawrence] Bragg for instance, who understood three-dimensional crystallography and their diffraction patterns very intimately. They understood that at a very intimate level having starting in the same way that Pawsey started. Pawsey started with cosine responses to a point source and the people in crystallography started with diffraction, Bragg diffraction, from regularly spaced atoms. And they understood that at a very intimate level. And then it became very, very complicated, but you could still understand that if you had lived through the subject. So somehow or other, Ratcliffe had picked up this mathematical type of knowledge, which was unusual for him. But his method of explaining it was entirely physical. What for you and me these days would be the shift theorem of the Fourier transform, for him was a prism. And a cosine, which we think of as having a transform which is two delta functions, to him that would be a statement that a cosinusoidally modulated screen up in the ionosphere would transmit two plane waves at angles of incidence to the normal given by the spatial frequency of this corrugation. So everything had an optical interpretation and would then, for the purpose of these lectures, was to facilitate the explanation of ionospheric phenomena.

Sullivan

Did you see at all the influence of this course on the work of [Martin] Ryle’s group?

Bracewell

Yes. Now let me see, many ionospheric projects, all of which were influenced by that work. But the influence on the radio astronomy? Well, yes, the first example one could mention would be [Harold M.] Stanier’s attempt as a graduate student, research student, to measure the intensity distribution over the Sun and by making simple interferometric measurements with trifling antennas in different azimuths and in different spacings over some length of time.

Sullivan

Right, I believe that was the first direct use of these kind of principles, but you do see that as sort of coming out of Ratcliffe’s course or understanding?

Bracewell

I don’t doubt that at all.

Sullivan

Yeah. Did this course have a strong influence on you or were you sort of a Fourier freak before you went to Cambridge even?

Bracewell

Well, I did know a lot about Fourier analysis because I had done my mathematics in a department which had grown up under [Horatio S.] Carslaw, who wrote one of the great texts in the subject. And although Carslaw had just retired at the time I began as a student, all his colleagues were the people from whom I learned mathematics, which was a very rigorous ordeal in those days. So I knew quite a lot about the subject but I had none of the physical interpretation of that. The only interpretations of that ever given by the mathematicians were in terms of synthesizing wave forms, but these wave forms were not physical wave forms. They would say, "Take a saw tooth wave form." Well that was not the output from any oscillator. So it was an eye opening experience for me to find Ratcliffe able to interpret all these things in physical terms and to exhibit the ability to reason in terms of physics with mathematical problems. You take the mathematical problem, you translate it into physics, do the reasoning physically, translate the answer back, and you’ve got a mathematical theorem. I remember him going to a talk which [B.] Van der Pol explained how a lightening flash in between two conducting planes would lead, in the distance where dispersion would have taken place, to a wave form that was a J0 Bessel Function. And he had proved this by some incredible integral, which was well beyond the abilities of anybody in the Cavendish. And Ratcliffe came back and reported this to us, and very cleverly proved that he already knew this in terms of multiple reflections arriving at the same receiving point with appropriate time delays. And he was able to derive the asymptotic formulas for the Bessel function in very simple physical terms. When you wait for a long time, this Bessel function has become a very slowly decaying sine wave and that of course is just due to multiple reflections which are more or less now vertical. So the time delay up and back gives you the asymptotic period and you can get the inverse dependence on time from, well, if I had a moment to think I’d tell you the whole thing. But it was quite a revelation of its kind, how something that was mathematical to him he looked at sort of scornfully. He admitted you could integrate this out, but he would take the attitude, "Well, why do that when it’s apparent if you think it would be so."

Sullivan

It is fair to say then that this kind of attitude of Ratcliffe had a strong influence on you.

Bracewell

Oh, indeed.

Sullivan

Certainly your textbook on Fourier transforms, the beauty of it to me is its physical insights.

Bracewell

Well, I hope you’ll buy a copy of the second edition. Yes, and I’ve got my debt to Ratcliffe clearly stated in the preface. And as a matter of fact, I sent Ratcliffe a copy of the book and he wrote back and said that he had been thinking of writing it up himself now that he had retired but since I had done the job he would put his efforts into a couple of other books that he had in mind.

Sullivan

Well, going back to the post war period, when was it that you went to Cambridge again?

Bracewell

1946.

Sullivan

Ok, so it was very early in the middle of these solar observations.

Bracewell

Yes.

Sullivan

Was there anything else you wanted to comment on about what you saw before you left?

Bracewell

A comment about polarization. I know that Pawsey did not go out with the intention of measuring polarization. That was done by D. F. Martyn at Mount Stromlo where [Richard v.d.R.] Woolley was the director at the time. So while there was a little chuckling this morning when it was mentioned that Woolley had been chairman of Commission 40 of the IAU [Radio Astronomy Commission of the International Astronomical Union], he did have some credentials at least through being administrative head of a place where the polarization of radio waves from the Sun was demonstrated by D. F. Martyn, by a very clever polarimeter that might not have occurred to everybody.

Sullivan

Now Martyn, of course, I can’t talk to. He didn’t build instruments, did he? He was a theorist.

Bracewell

He built instruments.

Sullivan

I didn’t know that.

Bracewell

Yes. I walked into his office at Mount Stromlo one day and he had a chart recorder running on the wall which was measuring the diurnal component of atmospheric pressure. And he had done this by connecting a barometer to a bottle stuffed with cotton so that the air could only get in and out very slowly, with a time constant of about a day. As a result the barometer was rising and falling with all the weather components filtered out and only the diurnal, and I’m not sure whether this was the lunar or solar diurnal, it must be the solar component.

Sullivan

It’s a tuned filter, right?

Bracewell

That’s exactly right. It’s not tuned, it’s just a low pass filter. And he was recording that…. Suppose you have a barometer rising and falling, how would you record the height? Well, he was doing that by shining a light on the meniscus and with photosensitive paper behind, who knows what the hell it was doing, but it sure as hell was drawing a line. And here it was at various amplitudes and phases running on and on and on. So he had instrumental ability. But in the case of the polarimeter, he had thought out how to do it. First he conceived the notion. I don’t know how that came about, but having got the notion in his mind, "Wouldn’t this radiation be polarized? If so, let’s look?" Well he must have looked for linear polarization first. I don’t recall that, but he must have rotated a dipole or a yagi. And he could do this with a single antenna, you see. This could be done with a single yagi antenna and he must have rotated it and not found any linear polarization. So he said, "Let’s look for circular." And he did that by making a T junction in coaxial cable, flexible cable, making one branch a quarter wavelength longer than the other and connecting these two branches to two yagi antennas. And then simply mounting them at right angles and moving one of them backwards by hand until it was a quarter wavelength behind the other to see what that did. And then he could move it a quarter wavelength in front. And he was able to show that there was strong circular polarization. And I don’t remember whether he got the sense correct or not, but at least he knew how to do it. It’s one of those subjects where you have to make an even number of errors to get it right.

Sullivan

And of course that result of his was published along with two other reports of detecting polarization of the Sun by [J. Stanley] Hey and by Ryle, and I gather then that from your knowledge that Martyn’s thing was just completely independent.

Bracewell

Certainly, quite independent.

Sullivan

They were all together in Nature in a couple of weeks. [Note added 2014: 1) D.F. Martyn. Polarization of Solar Radio-frequency Emissions. Nature 158, 308, 1946 (submitted 6 August, published 31 August). 2) E.V. Appleton; J.S. Hey. Circular Polarization of Solar Radio Noise. Nature 158, 339, 1946 (submitted 23 August, published 7 September). 3) M. Ryle; D.D. Vonberg. Solar Radiation on 175 Mc./s. Nature 158, 339, 1946 (submitted 22 August, published 7 September on the same page immediately following the Appleton and Hey article)]

Bracewell

I don’t recall that but if you go back and look at the dates of submission and so on, you might find out an interesting sequence of events. It might have been an artificial synchronization.

Sullivan

Now, that’s true. That does happen in some cases. I don’t remember in this case if it did or not.

Bracewell

As a matter of fact you are beginning to stir my mind there. This may be one of those dubious cases where we would have to check into that to know, which you could easily find out.

Sullivan

So you went off to Cambridge to get a Ph.D. basically?

Bracewell

Yes.

Sullivan

And why did you choose to go into ionosphere?

Bracewell

Well, I went in to see Ratcliffe when I arrived and he had in his hand a letter of recommendation that Bowen had sent to him. Bowen had been favorably inclined to the idea of my going on leave from Radiophysics to Cambridge. So he had written a letter and in typical Bowen fashion he asked himself what he should write that would ensure the success of this mission. So you’ll see what he wrote. Ratcliffe said to me he was very glad to have me there and he noticed all the good things I had done, and he was particularly pleased that I had had some previous experience with the ionosphere. Now, I am a very naïve person. I’ve learnt, but basically I’m a very naïve person. So instead of using my brain, I immediately said, "I have no experience with the ionosphere." And a frown crossed his face and his brow furrowed and he picked this letter and he looked at it very intently. He said, "It distinctly says here…" and I think he probably read me the sentence, and Bowen had perjured himself saying that this man had previous experience with the ionosphere. My interpretation is that the purpose was very simple, "Get the chap over there and they won’t send him back." [Laughter] So Ratcliffe didn’t worry about that and he must have filed that away for future reference. He never mentioned it to me again. And then he said we have several projects that might be of interest to you and he described three. And since I was there a little earlier than some of the other newly arriving research students, I got first choice. Now, I had the choice of doing something that was a relatively high frequency but I forget what. Now I had been working in microwaves right at the very end of the radio spectrum. And as a radio spectrum had moved up to higher frequencies, I had done so too. So I had been working on the fringe of the spectrum for a long time. Then he had some intermediate frequency thing, 2 or 3 MHz. And then he had a project at 16 KHz, that’s the frequency of the transmitter at Rugby. And I thought, "Well, I’m accustomed to working at the end of the spectrum. This is the low end of the spectrum so I’ll go there." That was my principle for choosing. I knew nothing whatever about the type of work involved. It turned out to be very interesting.

Sullivan

But there was no choice outside of ionosphere work? Because of this letter, I guess.

Bracewell

No, I had applied to Ratcliffe’s group on Pawsey’s recommendation. Pawsey knew Ratcliffe. We didn’t know Ryle. Ratcliffe everyone knew was a great man and of course he was the producer of Ryle in a real sense. So Ryle wasn’t known at that time.

Sullivan

Can you briefly tell me what your work was at Cambridge, in particularly what influence it might have had on later radio astronomy you did? I say briefly because it’s not directly radio astronomy I gather.

Bracewell

Well, most of my previous experience had been with instruments, either with electronics or with waveguide equipment. Microwaves, I became deeply familiar with microwaves and electromagnetic boundary theory problems that go with that. But my experience then at Cambridge for the next three years was entirely in observational work. The planning and executing of observations and as it happens building the necessary equipment, which was quite arduous and explains why one gets by with the minimum equipment when you have to build it oneself. You think very hard about what’s the minimum that will do it. If you have to order it and it is just a matter of paying money, you’ll do it a more complicated way. So I learnt there how to plan observations and think out observations in terms of equipment. That was a new sort of experience for me. That was couched entirely in terms of ionospheric measurements and rather simple electronics but the measuring problems were very delicate and interesting. I also then began picking up solar influences and that caught my interest because I had had some background interest in astronomical things. And when I found that we could see the Sun when we were picking up a radio transmitter, I became interested in that. And Ratcliffe wasn’t very impressed by that. He regarded that as a mild aberration and a diversion from my true duties.

Sullivan

You could see the Sun with what kind of receiver?

Bracewell

With a 16 KHz receiver tuned to a transmitter about 90 kilometers away. The effect is that there is an interference being the ground ray and the once reflected sky wave. And since the wavelength is about 19 kilometers, if the ionosphere happen to move down just a few kilometers then the two vectors that are combining would show a change in resultant amplitude. So that we could monitor movements of the reflecting level as small as a kilometer and probably less. And this is a very sensitive detector, we could see the effects of solar flares, which were much too weak to be detected as fade-outs on short wave.

Sullivan

But it could be detected directly by the existing (?)?

Bracewell

No, no. Not at all. And as for a comparison with the spectroheliograph, we were in direct communication with [M.A.] Ellison, who was the only person observing flares in Great Britain. And we would send him lists of flares, none of which he could see unless they were very big. For a long time he resisted the notion that we could detect flares that he couldn’t see. But whenever he got a thundering big one, we would send him the record and ours would be colossal. We had a very sensitive technique for that. And the first paper I wrote based on work I did in England appeared in the Monthly Notices with my colleague Thomas Straker on observations of flare effects on very long waves. [Note added 2014: Bracewell, R.N.; Straker, T.W. The Study of Solar Flares by Means of Very Long Radio Waves. MNRAS, 109, 28, 1949.] So there was a slight astronomical connection there, otherwise that work was…

Sullivan

Geophysics?

Bracewell

Right, you could call it geophysics. Yes.

Sullivan

What about your relationship now with the Ryle group? You were telling us at lunch about the Saturday morning journal club or whatever.

Bracewell

Yes, we would meet on Saturday mornings with all the radio astronomers and all the ionomers. And we would do various things. People would report on journal articles or they would report on work that they themselves had just done. Or there might be a discussion on some topic that had been circulating, instrumental problems that people were engaged on, how you would do this or how you would do that. One fellow was trying to make a machine for computing autocorrelation functions. There was an instrument somewhere which was churning out data on punched paper tape. And it must have been the intensity of some down-coming wave from the ionosphere or it might have been a phase. I think it was probably a intensity. The problem was, "What’s the autocorrelation function?" And a great machine was built into which you fed this tape and by banks of relays and other incredible telephone equipment, it would remember a hole that had gone by and would multiply it by another hole that had gone by. This was a total analog device. It looked like a Heath-Robinson machine. That sort of machine would be bandied about in discussion and people would argue about whether it was the right way to do it and usually they’d conclude that it was not a good way. And then the man would go away determined to prove them wrong and make it work over the weekend.

Sullivan

Over the next six months…

Bracewell

No, no, come back next week and say, "I told you so." Nothing like a little competition like that to stimulate activity.

Sullivan

So Ryle’s group at that time would be only one of many under Ratcliffe?

Bracewell

No, Ratcliffe lived in the old Cavendish, the old original building where the neutron had been discovered and so on and so on. And the nuclear and X-ray people had moved into the new building. So the ionospheric people and the radio astronomers were all in a sequence of rooms on the first floor [Note added 2014: not the ground floor]. So we were all in very intimate contact.

Sullivan

I see. And the ionospheric were pretty much one group and the radio astronomers a second.

Bracewell

There was a noticeable division there because Ratcliffe was directing all of us and Ryle was in charge of the other. Ratcliffe was nominally in charge of the whole thing but the de facto separation was quite clear.

Sullivan

Were you in frequent contact with the early students under Ryle or colleagues like[Frances Graham] Smith and who was that fellow, [Derek D.] Vonberg?

Bracewell

Vonberg, yes. I knew Vonberg. Vonberg graduated and took a job in industry or with the post office, I forget which. And I remember us all feeling that that was sort of a traitorous thing to do. Here’s a scientist just goes away and gets a job, throws away all his abilities for the benefit of mankind. So Graham Smith came along, I’m sure only a year or two after I did. But we all knew one another very well.

Sullivan

But you did not take part in discussions with them about the results they were finding?

Bracewell

Yes, they would discuss that on Saturday mornings. I don’t believe that there was any air of secrecy at that time that in any way compares with what later developed.

Sullivan

This business about Vonberg is interesting. I haven’t been able to track him down in England but was that a bit of a setback to Ryle’s group? I mean that was sort of half the staff that he had gotten trained more or less and he’s all of a sudden gone.

Bracewell

Vonberg was a tall, rather striking fellow, rather imposing, and it’s conceivable to me now, though I don’t know for sure, that there might have been an element of competition between the two of them, and that may have accounted for them splitting. But I doubt whether it represented any substantial loss to the activity, I very much doubt that. Like yourself, I’ve never heard of Vonberg since. I don’t believe that he had anything like the scientific capacities that Ryle had. I really don’t know, that’s just a guess.

Sullivan

Once again at lunch today you were talking about how you became in correspondence with the people in Sydney about what’s going on and would sort of stand up at these Saturday mornings. Could you sort of repeat what your role was there?

Bracewell

Well, when I arrived in Cambridge I found they regarded the work in Sydney as extremely backwards and I perceived immediately that this resulted from about an 18 month delay in information. When I left Sydney I saw advanced things being done and then when I arrived in Cambridge it seemed to me to be about the same, different, but similar state of development. Whereas their attitude was, based on what they’d just seen published, that they were well ahead of the competition and were in no danger of being overtaken. Well, it wasn’t like that at all. So I tried to disseminate a little information from Sydney and I published two or three short letters to The Observatory based on information that came through from Sydney with the approval of the management. I told them what I was up to. And tried to close that gap. I felt very idealistic. I suppose when you are young you do and I felt that a freer flow of information was a blow struck against entropy. One had a duty to do it.

[Note added 2014: The three articles to which Sullivan and Bracewell are referring are: Bracewell, R.N. An Instrumental Development in Radio Astronomy. Observatory, 70, 185, 1950; Bracewell, R.N. Radio Stars or Radio Nebulae? Observatory, 72, 27, 1952; Bracewell, R.N. A New Instrument in Radio Astronomy. Observatory, 73, 200, 1953]

Sullivan

And in fact, the first three the publications I have here on my list are Observatory 1950 through 1953 where you are talking about Payne Scott and [Alec G.] Little’s three element interferometer locating bursts, radio stars or radio nebulae based on [John "Jack"] Piddington minutes and [Bernard Y.] Mills’ observations, and then Mills Cross. But this radio stars or radio nebulae, it seems to me from reading that paper that it is more your synthesis of some information that they had sent you. Is that correct? You had more of yourself in that one. It wasn’t just a reporter.

Bracewell

Well, I was trying to behave like a reporter but also I have an interest in exposition. I like to try to explain things to other people. I’d have to look at it again to see just exactly what you are referring to. But that sounds about right. I would be trying to explain it a little better than the originators explained it. I think my description of the Mills Cross would be in that category. It’s not quite a good description where anyone can understand. And it’s not original. I’m sure Mills looked at it the same way. But whether he got it written up, I would have to look into the papers. But it was a good explanation of the Mills Cross and I tried to put that into the record.

Sullivan

Now it seems like from what you said that the Sydney people were willing to send you this information, that they were not fearful of…

Bracewell

I think that must have been written from Sydney after I got back.

Sullivan

’53 is the date on it.

Bracewell

Yes, well, I would have been back in Sydney then.

Sullivan

But when you were in Cambridge there was no problem…?

Bracewell

Well, there were communications taking place. I don’t know who Pawsey might have been writing to but Ruby Payne Scott was certainly writing to Ryle. Well, now that I’ve said that, I believe that is another way of saying that was Pawsey’s way of communicating with Ryle. I know from other examples. For instance, Pawsey communicated with Reber by having me write. And so this would have been his way of communicating with Ryle.

Sullivan

Why does he use this technique?

Bracewell

Well, I’ll tell you the Reber story first. Reber was on top of Maui and he was getting a little fed up with the circumstances there and had discovered that there is a hole in the ionosphere over Tasmania which nobody else knew. Well it was known because it was in the books as a matter of fact, but no one you met in the course of casual conversation knew that Tasmania was any different from any other equal southern latitude or southern magnetic latitude. But sure enough here is this hole over Tasmania having something to do with structure of the geomagnetic field I suppose, but never-the-less. But Reber had found that it would be the best place for him to peer through and that Maui was not as good as he’d hoped. So he wrote to Pawsey asking for assistance in setting up an installation in Tasmania. He wanted the Radiophysics Lab to back an ionospheric venture. Well, it was quasi-ionospheric because he had in mind that he would be able to peer through this hole and look at the galactic radiation from beyond. There would be terrible problems of diffraction, but it’s a clear, original idea, typical vintage Reber. No one else had thought of it and if they had, they wouldn’t have given it a try. So that perplexed Pawsey because although there were resources available, he wanted to spend these resources in the most scientifically productive way. It was very cost effective, the type of thinking he used to go to. But he didn’t want to offend Reber by turning him down. So what he did was also typical vintage Pawsey. He gave this to some rabid reviewer who in this case happened to be me. So he said, "What do you think about this? Take it away and read it." So I read it through and I found three or four things that were wrong, that were just not right. So I went back to Pawsey and gave him a little list, the sort of reviewing one does on a paper. My first comment, "This is all wrong." Second comment, "This is very dubious." Third comment, "This is jumping to a conclusion which is not substantiated." I was not taking a global view because it was not my responsibility to make a decision to commit funds or to embark on a new program. I was reading that paper in a microscopic, proofreading type of way. So I gave Pawsey my list of comments, most of which were negative as far as I can recall. And Pawsey then responded to Reber by sending him my handwritten, list of nasty remarks. So I discovered years later that Reber never forgot this. In case what I’m telling you now leaks out, I won’t report how I found out that Reber never forgot it, but I can’t blame him.

Sullivan

So this is how you ended up writing Reber?

Bracewell

That’s right. I never wrote the letter and as a matter of fact, Pawsey is not the one who told me that he sent this piece of paper.

Sullivan

Not even that?

Bracewell

I discovered this in a most indirect fashion, to say the least. Well in any case…

Sullivan

What about with Payne Scott and Ryle?

Bracewell

That would have been Pawsey’s way of communicating with Ryle. He would say to Ruby, "Why don’t you write to Ryle about this?" And she would write the letter, show it to him, I’m imagining, and he would say, "And you could also point out…" And she would send the letter. Now she was a pretty tough cookie. And she would write a non-diplomatic letter, all her speech and conversation was non-diplomatic, verging on rude. And so these letters to Ryle I think one could guarantee were of the nature, "I told you so," or "I told you so last time," "Only a fool would believe that." I’m sure they were very offensive letters, but quite in her normal, everyday style. And Ryle had corresponded with her and the argument they were having was over the existence of sporadic bursts. Now Ryle had put a lot of emphasis on the fact that you had to have a loud speaker attached to your solar recordings because hearing them permitted you to distinguish between non-solar phenomena, most particularly vehicles rumbling down the road. You could hear them coming and you could become acquainted with the sound and you would watch the chart recorder pouring out and if you heard ignition noise from the truck going by you would write that on the chart recorder. If an airplane was going overhead, at the same time there would be a little burst which of course would be of much shorter duration, just a spike on the record because the plane was only there for a brief time. So Ryle knew how to identify airplanes. But Ruby also knew airplanes. They weren’t as numerous in Australia, of course. So she knew she had things that were not airplanes, which she called sporadic bursts or isolated bursts. And Ryle had never reported these. Well, perhaps he had published a record showing one and she had written to him saying, "This is an isolated burst." And he written back saying it’s an airplane. So they had a couple of interchanges on this. And then when I got back to Sydney, I had some of Ryle’s records with me and Ruby immediately pounced on these and said, "There they are. There they are." And she probably wrote him a letter saying, "I told you so. There are these bursts all the time, you see."

Sullivan

These were the records you had looked at in connection with your ionospheric work. Apparently Ryle had let you…

Bracewell

Yes, I needed to make a correlation study between sudden phase anomalies due to solar flares and bursts of solar noise that occurred at the same time. And I have here with me a Xerox copy of one of these records that I am referring to.

Sullivan

From March ’47.

Bracewell

This jagged curve is the solar chart made by Ryle. It’s full-scale and hand traced. That is a hand tracing of which I made considerable lengths. That’s the 29th of March of 1947.

Sullivan

Of his original record, right.

Bracewell

As you can see there are two important bursts and then things got quiet. And then is a post burst increase that runs on for quite a long time…

Sullivan

Half an hour.

Bracewell

Coming later. Then the smoother curve is our record of what the ionosphere was doing. The ionsphere went down and then recovered slowly. It’s a very uniform thing. And undoubtedly this follows quite closely the integrated ultraviolet from the flare because it’s quite in keeping with the visible observations made with the spectroheliograph. We have many cases of the line widths measuring the spectroheliograph agreeing in the general profile with this. Of course, the visible ones usually started when the flare was near maximum because that’s the first time they’d see it. So our sudden phase anomalies always began before the optical observations. But as you can see from the second example I have here, we have a case where possibly the solar noise sets in a few seconds or maybe a minute or two before the phase anomaly. So this was the sort of analysis I was doing and all I can say is that the situation was then as it is now. The solar noise is a very irregular thing compared with the general course of the flare itself.

Sullivan

But your sin was in showing these tracings to…

Bracewell

Yes. Now Ryle knew I was making these because he had them filed in drawers in his office and I was there for days laboriously tracing these on long roles of tracing paper. Searching through my list of times and dates, finding his record, and if there was something interesting, as with these two cases, I would trace his whole record. He could see by the way by the interference pattern of his two element interferometer. That’s all superimposed on this. And quite possibly this diminution may be an interferometeric minimum but you can see there was a sudden cessation of noise but perhaps that minimum, which looks kind of round, we can tell by the timing you see. That’s probably an interference minimum. So you need skill to read those records but never-the-less. But these things here are quite possibly sporadic bursts. There are several of them. They are probably type three bursts and the kind of thing that was in contention.

Sullivan

It would occur to me that if this was one of his main early correspondence with Sydney, that this may have been something that turned him off to Sydney, this kind of treatment from this Australian woman.

Bracewell

That’s possible.

Sullivan

I just don’t know. Well, the next publication I have in your list, actually there is one other before we get to your textbook. Bracewell and Roberts, ’54. [Note added 2014: Bracewell, R.N.; Roberts, J.A. Aerial smoothing in radio astronomy. Aust. J. Phys., 7, 615, 1954] When did you go back to Australia now?

Bracewell

In 1950.

Sullivan

In ‘50, I see. So well then the question is before we get to ’54, what things did you start working on?

Bracewell

Well, for two years I did ionospheric measurements in Australia similar to those I’d done in England. As a matter of fact I made very long wavelength observations on the boat on the way back to Australia. I had a little room on the bridge and an inverter and I made observations of GBR [Note added 2014: radio station] for thousands of miles. And then I continued that sort of work in Australia, working with Keith Big, who later became famous for discovering the control that Io exerts over Jupiter radiation. So he and I rattled around New South Wales to different distances from a transmitter and made lots of observations. I did that for a couple of years. And the data that we had accumulated disappeared one day. I had books full of data, so no paper was ever written on that. I expended two years of my scientific life, and all the data disappeared.

Sullivan

Could you be a little more explicit about disappeared? Stolen? Taken by the trash man?

Bracewell

Well, it sure as hell wasn’t taken by the trash man because we had quite a lot of it distributed around. I don’t believe that explanation. Just how it disappeared I don’t know.

Sullivan

Well since it’s not radio astronomy data I won’t probe any further.

Bracewell

Perhaps in the course of your inquiries you could ask people.

Sullivan

Right, "Did you take Ron Bracewell’s data in ’52?"

Bracewell

I think it would have happened in ’52.

Sullivan

Someone trying to get you off this project.

Bracewell

Well they got me into radio astronomy. So in 1952…

End of Tape 131A

Begin tape 131B

Sullivan

Continuing with Ron Bracewell on 8 January 1980. Well, in ’52 when by necessity you had to change your course, you told me that Pawsey asked you to take on administrative tasks, basically.

Bracewell

Yes, to organize the 10th General Assembly of URSI, as organizing Secretary. The Committee in charge consisted of Bowen, Pawsey, D.F. Martyn, and Sir John Madsen as chairman, and maybe one other person. They would hold regular meetings well ahead of time and decide what was to be done and I had to execute it. And they said to me, “You have all our resources. Just tell us what you want done but you do it.” And it worked out that way. I had appointed dozens of committees and was at the head of a huge pyramid. That was a very interesting experience, it used up about six months. I designed the URSI flag, which is still flown at General Assemblies to this day and was first flown in Sydney in 1952. We invented the colors, which are gold and blue, and the flag was made by a committee I appointed.

Sullivan

Was that where the diamond shape came from?

Bracewell

No, no. The flag doesn’t have that. And it was first hoisted by [Edward] Appleton outside the Peter Nickel Russell School of Engineering in 1952. And there is a photo of it being hoisted. So that was very exciting because all of a sudden the names that had become familiar to us from papers from many countries suddenly materialized as faces. And we saw people from France. Jean-Louis Steinberg was there and later to become head of the radio astronomy at Nançay and then to move on to head of their space physics. And [Marius] Laffineur, who was the chief moving force at that time.

Sullivan

The Reber of France, I think of him as.

Bracewell

Reber of France, yes. And we met a number of Americans such as John Hagen and – I don’t believe [Fred T.] Haddock was there. Two other Americans were Larry Manning and Bob Helliwell, who moved on to capitalize on the discovery of whistlers and convert that into a whole new field of science, which has been amazing. And assorted people from strange countries in small numbers and then a contingent from England of the figures that are still well known. So it was a very interesting meeting. There were no parallel sessions that I can recall. Everyone took in everything and there was a very nice central assembly room with free coffee. So I think it was a great success and was instrumental in lubricating contact between the major groups.

Sullivan

Did you write more freely to other groups, do you think, after that?

Bracewell

I don’t think there is any doubt. It helped enormously. Graham Smith was there. Ratcliffe was there. Ryle didn’t come.

Sullivan

Did it change what you and others decided to do at Radiophysics, which experiments to do?

Bracewell

It probably meant that considerations were taken into account that we were previously ignorant of.

Sullivan

What was your next task after the URSI?

Bracewell

Pawsey wanted to write a book. And he said, “The time is ripe. We have reached the point where there is a kind of plateau and we are re-gathering our forces. Lots of discoveries have been made in several fields, and the next round of discoveries will require bigger instruments, and they’ll be breathing space while this happens. So let’s fill in the time writing a book. Now is the right moment.” Well, of course, it took two years to write. And I don’t know whether there ever was a plateau, but still, that was that. Now he didn’t want to pull the leaders of the principal groups off their work for that purpose such as [J. Paul] Wild or Mills or [Wilbur Norman “Chris”] Christiansen, who would have been perfectly rational choices in terms of their writing ability. I see now looking back on it he had a slightly delicate job because there may have been some feeling of resentment that a person like myself who had been working mainly in the ionosphere should now be working in radio astronomy. But the logic of it was quite strong. My work in the ionospheric research was running down and a six month gap had intervened and I’d lost my momentum, as well as losing a lot of my observations. And so it made sense and I enjoy writing. So Pawsey sold that choice to the rest of the group without any apparent ripple and we worked for about two years assembling chapter after chapter and revising, and revising, and sending these chapters around the lab for someone or other to read who would be an appropriate choice.

Sullivan

And did little else for those two years?

Bracewell

I essentially did nothing else. No, that’s exactly right.

Sullivan

This obviously gave you a chance to really review the status of radio astronomy.

Bracewell

Well, I read everything that had been written. I already read everything that had ever been written on the Sun before I began that. I had read all the journals that published solar observations. In fact, I read several journals backwards starting from the present and just read them backwards into time. So I was thoroughly familiar with that side but I had to learn a lot of other subjects. And so I was reading voraciously and at the time writing. You may recall that in that book there are some introductory chapters which purport to give the status of the subject at the time. There would be some astronomical background and that thing. And in some cases that material was rather hard to come by. We didn’t have any one to consult. On interstellar matter for instance I don’t believe there was anybody in Australia who could tell you about interstellar matter who had worked in to or knew about it. So I found myself reading some strange things. Fortunately I could read some other European languages so that I wasn’t particularly held up by strange references. But that’s mostly what I did.

Sullivan

One thing along that same line is that I’ve been struck that there is no mention of the synchrotron mechanism in your book which speaks to the fact that it was just not being considered from your point of view or probably in world radio astronomy as anything of importance; even though by late ’53 or mid ’53, whenever you sent the final version of the book off, there had been many books published in Russia.

Bracewell

Well I was totally ignorant of anything that was happening in Russia. I don’t recall that we had any Russian periodicals around, except maybe some standard things in physics. But I don’t even recall that.

Sullivan

It could very well be.

Bracewell

I’m not entirely sure of that but I certainly don’t recall it. I was studying Russian, and so had there been material I needed to read I would just have incorporated that into my interest in studying Russian. But I was quite unaware of anything happening in the Russian language. Except for we did know about an expedition that the Russians had sent to Brazil. But that was easy to find because it was of a radio astronomical context. But anything that might have been written connected with plasma physics, I’m not sure how we would have keyed into it, and as we heard [Jan Hendrik] Oort brought it to the attention of other Europeans.

Sullivan

Well, this may have been part of the motivation to start the whole Radiophysics Abstracts business, which did consider the Russian literature once they got started. They get started in ’53 or ’54.

Bracewell

Well I don’t when it began. I know that we had the Cornell Abstracts, which Martha Stahr Carpenter was preparing very ably. The Radiophysics Abstracts were appearing simultaneously with her for some period of time but I forget the details.

Sullivan

Well ’54 is when the Radiophysics Abstracts got going in a big way. There was some earlier…

Bracewell

Well, she ran into troubles and then Radiophysics decided on the basis of some international symposium that they would take over that duty.

Sullivan

No, it went on for quite a while in parallel. Do you have any particular thoughts on radio astronomy at that time, 1953, since you did pause and review the whole deal? What stage was it at? Where was it going?

Bracewell

Let me just make another comment about synchrotron radiation. Pawsey and I both knew about magneto-ionic theory so gyro-resonance or cyclotron-resonance or anything that was connected with magneto-ionic theory was something we could conceive of. Now we also knew about accelerators, now that I come to think of it. As a matter of fact, Mills had built a linear accelerator and he did that in the same room as myself and we used to wonder whether we’d get cancer and things like that. And Pulley [Owen O. Pulley], who you may not have run across as a figure but was one of the contemporaries of Pawsey, who was a significant figure at Radiophysics, Owen Pulley, he knew about accelerators. But I’m not aware of ever thinking about synchrotron emission. We may have known about synchrotrons and betatrons. But synchrotron emission as it is now expounded, in a very elementary way, of course, I have just no recollection of it.

Sullivan

It had been suggested in 1950 by [Hannes] Alfven and [Nicolai] Herlofson and by [Karl Otto] Kiepenheuer in Phys Rev. but those articles were largely ignored except by the Soviets. [Note added 2014: Phys. Rev. 78, 616, 1950; Phys. Rev. 79, 738, 1950]

Bracewell

Yes. Well, we had different sorts of responsibilities. Pawsey had a global responsibility for determining which would be productive lines to go in. Now, generally speaking that meant, he would go tearing off on some observational project involving the development of instruments. Theoreticians were not very highly regarded around Radiophysics. People did it by their own inclinations but they had to be pretty good to cut much ice with Pawsey. They had to come up with something really brilliant that he could understand or he wasn’t terribly excited. So we had plenty of amateur theorists. Now, people generally speaking had very specific duties. The work was carved up among the available people. We would discuss who should do what, what was within the range of what could be done, and the timing with which results might come out. And then we would bury ourselves for months at a time, wiring things up, you know, stringing antennas up and doing that. So when you have a hierarchy of that kind the underlings are not likely to think in a global fashion. There would be one or two people doing that and then one or two others who just think of something original anyhow. Now Pawsey was very amenable to taking off in any direction that was profitable if you could convince him.

Sullivan

No, I see what you are saying. But what about back to an overview of radio astronomy?

Bracewell

Well, it was a hodgepodge thing. There must have been six or seven totally unrelated subjects. The Sun had nothing to do with the galactic radiation. And the discrete sources had very little to do with the galactic. And then there were a number of other things which were important for a time. Lunar radiation was quite important, and the study of meteors. Then the hydrogen line came along. All of these things were totally unrelated then. So when in 1954 I went to Berkeley to spend a year there giving lectures, I was able to lecture for a straight year on an incredible mixture of things. I didn’t have to stop once…

Sullivan

It was just radio astronomy?

Bracewell

It was radio astronomy and nothing else.

Sullivan

And later…

Bracewell

Well, I wouldn’t…

Sullivan

The meteor…

Bracewell

I may have mentioned meteors. I forget. I didn’t know anything about that except the theory of reflection which I thought was sort of beautiful. So it was all disconnected and, of course, disconnected from optical astronomy. We knew solar astronomers.

Sullivan

At Radiophysics, you mean?

Bracewell

Yeah, the people at Radiophysics were in contact with Mount Stromlo, with people who observed the Sun. I spent several weeks myself peering through a spectroheliograph. So I found that congenial.

Sullivan

Who would be the main people at Stromlo who were interested in this kind of contact?

Bracewell

Well, David Martyn was there. He had been chief of Radiophysics and Cla Allen who wrote the famous Astrophysical Constants. The other important figure there whose name is not coming back to me for the moment but who stammers was there also [Note added 2014: S.C.B. “Ben” Gascoigne]. There was another man whose name I’ve forgotten. Anyhow there was no lack of contact.

Sullivan

They were all interested in the radio stuff? Didn’t look upon it as being a bunch of engineers who don’t know anything about astronomy?

Bracewell

I don’t think it was anything like that. You see, we weren’t engineers, to a large extent. Those people were physicists and they regarded themselves as physicists. I had a Ph.D. in physics and my passport said “physicist.” Matter of fact, I think it still does. So we did indeed have people who were engineers and regarded themselves as engineers but the pecking order definitely had the physicists running the place. Most of the people had degrees in physics.

Sullivan

This strikes me. This is a difference with the U.S. where the early radio astronomers were pretty much all engineers and therefore it may have been a bit harder to bridge that optical/radio gap in the U.S. I’ll have to think about that.

Bracewell

I’m only referring to, well at the moment, to solar but now that I’ve come to think of it the connections with the Magellanic Clouds were quite good too. And that one time you know [Gerard] de Vaucouleurs lived in Stromlo for a time and he was frequently seen at Radiophysics with his beautiful wife. And I don’t think there were any great difficulties but there were not an enormous amount of optical astronomy taking place in Australia. There were no great telescopes there at the time. And the quantity of staff was rather small. The Observatory at Stromlo for instance was in charge of time keeping for Australia. That would have been a quite noticeable fraction of the whole set up.

Sullivan

So having finished the book, you say you went to California.

Bracewell

Yeah, [Otto] Struve arrived to see what all this was going on in Australia and he asked Pawsey to send someone to give lectures for a year. As a matter of fact, he invited Pawsey to come and give lectures for a year. Now Pawsey didn’t wish to do that and I was an obvious choice because by that point I knew more radio astronomy than any single individual except for Pawsey. I knew all the other subjects, you see. We had a bunch of experts and I was a generalist at that point. So I was the obvious choice. So that’s how I came to set foot in America.

Sullivan

I see. And did you while here visit any of the radio astronomy groups undoubtedly at NRL and let’s see what else in ’55, not much.

Bracewell

I’m pretty sure I went to the Carnegie Institution and met [Merle] Tuve and [Kenneth L.] Franklin and what’s his name?

Sullivan

Bernie Burke?

Bracewell

Bernie Burke. Don’t tell him I couldn’t think of his name. And John Firor. I remember all those people. And Howard Tatel. And they were working busily on the hydrogen line and assorted other things including of course Jupiter. But well, I’m not sure exactly when I went there but it was either in 1955 or ’56 because I was back again in ’56, you see. So I definitely went to NRL at a very early point.

Sullivan

What was your impression of NRL, the work they were doing?

Bracewell

Technically that was a pretty high caliber. First of all the 50 foot dish was a great tour de force, which was very impressive. Not appreciated by everybody but it is a very impressive thing. And the electronic techniques that they could muster there were of the highest caliber and the many great experts. Just seeing them making a matched load was pretty impressive. I understood all these things from having worked with microwave equipment. When I saw how they made matched loads, which I thought I knew an awful lot about, I saw they knew a thing or two. So the level of technology there was very high. And they were also doing something right in respect to their science. Although there has been a certain amount of turbulence there and complaints from the workers about the management, mostly Haddock complaining about Hagen, they were doing something right. We could get a whole long list of bungles that were made but that was a very productive operation.

Sullivan

I’d be interested on your opinion. I imagine it wasn’t the Cavendish style of doing things.

Bracewell

That was nothing like the way that the Cavendish did things.

Sullivan

Because there was much more money available I suspect.

Bracewell

Well there were resources and facilities. If you wanted something manufactured you could have it drawn up by a draftsman who knew what he was doing and could design things as he drew. And then you could have it put into the machine shop and someone who really knew how to fabricate things would make it with some years of experience because you had continuity of teams that had worked together for some years. That’s a tremendous resource and that was never broken up.

Sullivan

That’s true at Radiophysics too.

Bracewell

That was also true at Radiophysics. The atmosphere at NRL was not unlike what I was accustomed to at Radiophysics. So they could really move and on sizable projects, with all the backup existing. Now the Cambridge situation was quite different and Ryle operated in a completely different way. He would select out one option among those he could choose from which would require technology in favor of one where he could get to the result more directly. He was following the standard Cavendish tradition there, which I learnt a lot about. Of course, I already had that before I got there because I got it from Pawsey. So I appreciated both those ways of going about things and you take your choice, you think out the whole problem before you move.

Sullivan

Were there other places in the US that I missed that you visited? I’d be interested in your impressions.

Bracewell

Well, I went to Ann Arbor, Pontiac [Michigan] in 1955, about July or August. When the school year finished at Berkeley, I went traveling around and I went to Pontiac. And I stayed there overnight in a hotel and I got there by bus from Columbus, where I had just been to Indiana and see, Frank, what’s his name…?

Sullivan

Edmundson

Bracewell

Edmundson, who somehow I had gotten to know at Berkeley. And while I was sitting in my hotel room in Pontiac, having come by bus, I heard on the radio advertising that you could get a used car for $50. So I found that it was on the same street as the hotel and I had $50. I walked out and it was the middle of summer so it was still quite light. I walked up the street and sure enough here’s this place. I went in and said, "I came in to see about those $50 cars." The man said, "What $50 cars?" I said, "I just heard about it on the radio." He said, "We sold it, but we’ve got one for $75." So I bought a Pontiac in Pontiac. And then the next morning I went to see the solar installations, McMath-Hulburt installation. I was already acquainted with Helen Dodson by having written to her many times in connection with the sudden phase anomalies I’d observed in Cambridge. I was delighted to meet her and Ruth Hedeman. And [Robert] McMath was there and he was treated as a very important man. Orren Mohler was also there. So I was ushered into McMath’s office. I felt as though I was visited General MacArthur. It was quite an eerie atmosphere of very big boss. Well, I found him a very impressive fellow, and he asked me a few questions and then he said, "Are you going to Ann Arbor." And I said, "No, I’m going to Annapolis." And it was in the opposite direction, you understand. So he said, "I advise you to go to Ann Arbor and see Leo Goldberg. It might be to your advantage." Very cryptic statement, very brief, "It might be to your advantage." Being an obedient person, by golly I did. And it wasn’t to my advantage at all except for the pleasure of meeting Leo Goldberg for the first time. But it turned out that Goldberg was looking for an appointee to a job, which was given to Fred Haddock. That enabled Fred to escape from NRL and led to the development of very significant radio astronomy at the University of Michigan.

Sullivan

Did you see John Bolton’s operation in this first year or so when he came.

Bracewell

Yes, I visited Palomar and he had set up an antenna there. And I arrived within a few hours of him making his first transit observation of some source through his antenna, 30 foot antenna [Note added 2014: actually 32 foot], I would say roughly. And the exciting news was that the beam width was narrower than theoretical. As a matter of fact, I have a copy of that record. He must have been so proud of it. I have a copy, but it has no scales or date on it, but I remember what it was.

Sullivan

Now theoretical being ?/D or 0.22?/D?

Bracewell

With Bolton and [Gordon J.] Stanley you never knew but they always had something surprising to tell you. And the news was, "This is narrower than theoretical."

Sullivan

They told you, I see.

Bracewell

And you would open your mouth in amazement and before you could recover they’d amaze you with something else. They had their own peculiar kind of one up-manship. And they didn’t care whether they damaged their reputation while telling you this.

Sullivan

You haven’t mentioned, it occurs to me, Bolton’s name in all of this talking about Radiophysics.

Bracewell

Well, Bolton was in Sydney when I arrived back in 1950. He was not there when I left. So he must have arrived about ’47 or ’48.

Sullivan

It was ’47 I think.

Bracewell

So he was working at the station at Dover Heights and had already obtained records of several sources. And all that I can recall now on my first visit there was being in this concrete block house and seeing a chart record pouring off, which was from a receiver of such good sensitivity that the galaxy was continually pushing it off scale. And then you would reset the recorder or it would reset itself automatically with a switch, and switch in a little voltage and go back to the bottom of the chart. And after it had run off scale several times along would come one of these fascinating sources. And this was being done with the antenna above the sea and therefore it would show up as a fringe pattern. And you could see indications of very faint ones, which if you turned the gain up no doubt would also be sources. Now of course as you know the switched interferometer had been thought of in Cambridge to get rid of that embarrassing background. We don’t always remember that now, but it was a result of high sensitivity and the galaxy pushing you off scale.

Sullivan

Too much dynamic range.

Bracewell

So they were just working on schemes on suppressing the background. Now Bolton I think worked pretty hard out there. He always liked to dig holes himself and mix concrete. And we didn’t see him much in the lab, very rarely in fact. He just used to go straight to his little concrete blockhouse and work on antennas and receivers very hard, putting things together. So I didn’t have very much contact with him, certainly during ’50 and ’51. All I can say is that I didn’t see him all that much.

Sullivan

Ok, going back to his comment about narrower than theoretical, this was said to you, of course, because of your work at the time…

Bracewell

Oh, they probably said it to everyone. I don’t know how they did the theory.

Sullivan

But that does anyway get us on to your tremendous amount of work in the late ‘50s, primarily on beam sharpening and resolution and strip integration. How did you get off on this general stream to begin with?

Bracewell

I can answer that quite clearly. Pawsey and I had to write an early chapter that explained that different source distributions could look the same when scanned by an antenna. One was acutely aware that a double source, if the components were close enough, would look the same as a single wide source. And by calculation of artificial records you could convince anybody of this beyond a shadow of a doubt. So the question was, "If you make a certain observation, what’s the most you can say about the source." So I embarked on some calculations to see what I could find out about that. I calculated a few empirical cases. And then it suddenly struck me that the antenna is a low-pass filter. Now that is so common place today that we even say that an antenna has a transfer function. We forget that that term was borrowed from filter theory. Now we know that the mathematics is identical but the mind doesn’t work that way. A waveform which goes through a filter is something that is a function of time, voltage is a function of time. And the mind doesn’t deal with that in the same bin as images, which are two dimensional, spatial things. But nevertheless the analogy is there and all of a sudden we hit on it. And for weeks and weeks we used to tell anyone in the tea room that would listen that what the antenna is doing is being a low-pass filter. Well everybody knew about the pattern of an antenna. That was the only thing we knew about it. So the question is, "What is the filter function? What’s the filter characteristics, or what we would now call the transfer function?" And we found out that that was the autocorrelation of the aperture distributions. We knew about aperture distributions because of the Fourier relation with the pattern. But nobody knew about filter functions. So we got that into the book, and I think that was very influential in alerting everyone. And it is so clear and well explained that I don’t think anybody recalls that it was actually invented at one point. As far as I know, that description in the text book is where…

Sullivan

What you are saying is that your mistake was in not making it erudite and obscure enough in your initial exposition that it was clear it was new.

Bracewell

Well there were lots of things like that in the book. In fact, in the lunar chapter there is new material that was never published in any other way. But it’s never referred to; people who read it in a book assume that it was taken from some previous paper.

Sullivan

That’s right. So it was basically writing the book that got you off on thinking about all these issues.

Bracewell

Yes. In 1954, I was assigned the duty – Pawsey was going on a trip abroad and before he did so he had a big organizational meeting and assigned duties to everybody and appointed a committee to be in charge while he was away. And I discovered the other day that I was a member of the radio astronomy committee in his absence but I must have been the youngest of that group because Frank Kerr, who is older than I am, and by quite a margin I suspect, maybe five years, which was almost infinite in those days, he was almost a contemporary of Pawsey’s, you see, and he was Pawsey’s lieutenant in many circumstances. But on this occasion Pawsey left a written record of who the committee was and which things they were responsible for. Also in that document everybody was assigned some duty and my duty consisted of just four words, "Aerial smoothing, strip integration." That was 1954. In 1954 I’d already finished the first paper arising out of the book, a paper that was joint with Roberts, and I was beginning to look at two dimensional aerial smoothing and the inversion of strip integration, which had become a serious problem for Christiansen’s observations. And the reduction was being carried out by [Govind] Swarup and I used to look over his shoulder and see him laboriously trying to invert strip integration by guessing the answer and then he would compute the strip integrals by hand, adding up numbers and compare that with the scans. And in one or two stages of fiddling, you could do that inversion. Well, the theory turned out to be fascinating and I had written a couple of internal reports. I remember writing an internal report called Abel Transform. It was a gadget, a computer, which took Abel transforms, and it could be made to convert Abel transforms by a simple feedback system. So the idea was you put in the waveform and the output waveform would be the inverse Abel transform. Well, that’s for circular symmetry. It was a kind of curious concept. No one ever built the computer to do that. There’d be a few extra quirks to it in order for it to work. But the general strip integration problem turned out to be absolutely fascinating. And I finished writing that paper while I was in Berkeley and it was submitted at the time I got back to Sydney from Berkeley. [Note added 2014: Bracewell, R.N. Strip Integration in Radio Astronomy. Aust. J. Phys., 9, 198, 1956.]

Sullivan

Well one thing that usually gets a bad press I think in your work is the business about sharpening up resolutions and so forth. The general idea is that there was a lot of enthusiasm in the late ‘50s that one could do a lot better than nature really allows and you’re often named as the culprit. Is this a fair thing? Was there a bit too much optimism or people misusing what you were saying?

Bracewell

I don’t think that’s an accurate story. The first paper was one by Bolton and [Kevin C.] Westfold in which they proved by matrix algebra that you could invert the aerial smoothing problem and they gave the solution. [Note added 2014: Bolton, J.G.; Westfold, K.C. Galactic Radiation at Radio Frequencies. I. 100 Mc/s. Survey. Austr. J.Sci. Res. A, 3, 19, 1950] Now not everyone could read all this matrix stuff, and I’m quite sure Bolton couldn’t, so we may assume Westfold wrote it. And Westfold knew nothing about physics. Now they are all friends of mine so I’m sure they will recognize that those are true statements. Well, Westfold may know something about physics now, but he was a pure mathematician at that point. So here they purported both in words and in symbols to have inverted the problem. Well I found a mistake in that, and so my discovery…

Sullivan

And what error now are you saying? Their thing was in ’50 and yours…

Bracewell

That is wrong you see.

Sullivan

When did you publish yours?

Bracewell

In connection with writing the aerial smoothing section of the book.

Sullivan

’53 probably.

Bracewell

Well, it would have been ’52 or ’53, probably ’52. It was probably written quite early on. It was probably ’52. And I discovered some frequencies were wiped out entirely. Nobody knew that. People knew there was a smoothing effect but they hadn’t thought of it as a filtering effect in terms of spatial frequencies. What I discovered was two things: a band of frequencies is entirely wiped out and another band of frequencies has the relative strength upset. So once you knew that you could see that Bolton and Westfold couldn’t possibly be correct because you can’t get back things that aren’t in the data. But there is one thing open to you and that is to restore the balance of the thing whose balance has been upset. And if you do that you get a solution, which I called the principal solution, and a term which is very generally used now. But we also very soon discovered that the principal solution is not acceptable for many purposes. Very often it oscillates and goes negative for example. But I also discovered that that’s not the only solution, that there are many solutions. Now I never personally sharpened up or restored any observations that I ever took so I don’t think you have an accurate report of my role in aerial smoothing. I never sharpen up any observations I took.

Sullivan

Would you say that your papers never gave anyone else any false optimism about restoration? I mean you can’t be held responsible for…

Bracewell

Well after you’ve explained the whole theory, and I’ve just explained it to you in words very clearly, it’s very simple you see. There is a band that disappears. There is a band that is upset. You can restore the equilibrium. You can put in invisible distributions. You can get physically unacceptable things. That the whole story. That’s my contribution to it.

Sullivan

Let me do it this way. As you look at the work that people were doing in the late ‘50s, did you see violence being done to data in the name of Fourier theory or antenna beam restorations, these types of things?

Bracewell

There must have been one or two papers. But look: Hey, Parsons, and Phillips did a sky survey [Note added 2014: Hey, J.S.; Parsons, S.J.; Phillips, J.W. Fluctuations in Cosmic Radiation at Radio-Frequencies. Nature 158, 234, 1946], which they restored, and I don’t think there was anything wrong with that restoration. They didn’t have the theory of it, so they may have overdone it, but I suspect not because they only put in one correction term. And we know they would have done partial restorations, so they sharpened it up a little bit. Now to my mind that was perfectly alright. Now there may have been one or two papers but I can’t recall who. There certainly was an air of optimism around in some circles. I agree that I remember that. In fact there were fanatics who thought you could get the original distribution back. But that’s not my fault, you see, because it had already been claimed that you could. As a matter of fact Hey, Parsons, and Phillips in their text probably implied that their operation, if continued for two or three terms or so, would produce a true distribution. I’m not sure that they do say that but they may very well imply it. It sounds plausible, you see. You find something which, when you smooth it with your antenna, reproduces what you observed. It sounds quite plausible. But the fact that the series converges was not proved by them. I proved that it converges. And furthermore I found out what it converges to, which is not the true distribution. So my contributions were entirely theoretical, and I accept no blame for the false optimism of those utilizing the information provided.

I do have a further thing to add though. I found out another thing in that theory which didn’t come out until 1958. And that is that is the optimal restoration when you know the statistics of the noise. Now I believe I discovered that restoration requires a knowledge of the statistics of the noise. That was a new contribution. And the correlation between the noise and the signal, something that nobody had ever thought of, enters into it too. However the computation required to do that sort of thing in 1958 was unreasonable, and as far as I know was never applied. But the situation has now changed where we are in a position to make use of that 1958 result because a computer could do it for us. But I am not aware that anybody has ever made the necessary statistical analysis of their noise or of the correlation between…

End of Tape 131B

Begin tape 132A

Sullivan

Let me just ask you for the record, it would seem to me with your deep understanding of the performance of antennas and the nature of design of antennas and so forth that you might have some interesting things to say about the controversy between the log N-log S counts of Mills versus those of Ryle that went on in the late ‘50s primarily, because I see it as being largely a matter of really understanding the transfer function of the instruments. Maybe you don’t agree with that.

Bracewell

Well when you consider that lots of side lobes were just lumped in, I’d have to agree with that. Then of course some of the very early ones I would see. I lived in the same room with Mills and [Harry C.] Minnett for some time and then with Christiansen. So I would see Mills getting a letter from Ryle or opening up the latest publication and here would be a new log N-log S plot. And Mills could tell the name of each dot and he would look at these dots, which were anonymous, and he knew them as personal friends. And he’d say, "Yes, this is all very well if you try to do cosmology with this. But suppose you take out the Crab Nebula," and he would remove that one. And then remove all the other galactic sources, supernovae and what not, "Look what happens then." So he would redo this thing laboriously and show that that completely altered the result. So for a long time there the situation was polarized on the basis of inadequate presentation of data. Inadequate data I suppose. Then, of course, the question of confusion and the use of surveys that were totally falsified just made it more complex. It’s not a subject I am a great expert on. But I followed it with an amateur interest, but never got my own hands wet with it.

Sullivan

A related question that you may or may not have been involved with was the question of aperture synthesis and its development. Do you see that as being sort of a smooth development really going right back to Pawsey, McCready, and Payne Scott, right up through the One Mile and the Super-synthesis?

Bracewell

No, not at all.

Sullivan

How would you characterize that?

Bracewell

Well I don’t think aperture synthesis started off with Pawsey, McCready, and Payne Scott except for the extent that it might have suggested the idea to the Cambridge group because aperture synthesis was practiced in Cambridge. I don’t think you could really say that was the way in which the Sydney people thought at all. They didn’t really do that.

Sullivan

What was the difference?

Bracewell

Well, see, Ryle made use of small antennas and exchanged hard work. So he would have some research student like Stanier, for instance, slaving day and night, moving antennas during the night and observing during the day until he’d observed the Sun with just a couple of virtually, just dipoles, but with many, many locations. Of course, in the couple of weeks taken to do this the Sun has rotated quite a bit so it’s not surprising that you come out with a sort of smeared out Sun and any limb brightening that might be there or any point sources that might get lumped together in the middle. So they missed the limb brightening. But that was the sort of procedure that Ryle preferred to follow, to use minimum equipment and then expend a lot of time and effort. Now the technical resources at that time were generally greater in Sydney. Ryle was starting at a lab where there was no accumulation of equipment whatever. He had moved there from TRE [Note added 2014: Telecommunications Research Establishment, at Malvern] and there was nothing there. Whereas in the Radiophysics Lab there was a major workshop, going teams of drawing offices, machine shop, electronic technicians, a full facility. So they could move on to bigger things. So you see things like Christiansen’s original array of 32 dishes, quite an elaborate machine for its time, although reminiscent of a Cambridge tradition very definitely. But on a much larger scale, and followed by a second array, which he built perpendicular to that. And then we have the first Mills Cross, which is a big installation in itself, though we would think of it as small now but that’s only because Mills got them up to a mile long. So aperture synthesis in the notion of doing it square by square on a chess board. I’m thinking now about the paper describing aperture synthesis was not something that was developed in Sydney. The only connection might have been the Fourier transform formula that McCready, Pawsey, and Payne Scott gave out. In fact, I’m sure there was a connection there because that paper was read very carefully in Cambridge. That paper beat the Cambridge group to the identification of the location on the Sun, the diameter on the Sun, and the height. In all those things the Sydney group came in first.

Sullivan

Then what would you say was the concept – because once again you cite Stanier’s work but Mills also was going out to longer spacings, putting together a visibility function…

Bracewell

That’s quite right but that’s the great special undertaking to measure the diameter of Cygnus A. That is an example of that sort of aperture synthesis, though only in one dimension. But it had a very specific aim to get to such a spacing that the visibility would be seen to no longer be unity so that you could give a diameter. And as you know he used a radio link to get rid of the cable attenuation problem. Graham Smith just used a longer cable and put up with the attenuation. And [Robert] Hanbury Brown did it with his own inimitable invention. And they all got the diameter at about the same time. That led to nothing in Sydney. They may have been another example later. As a matter of fact I think [Peter] Scheuer spent a year or so in Sydney and did something along those lines. It could be regarded as a continuation. And as a matter of fact there was another example, the Christiansen Cross, elements of that were used as two element interferometers. But that’s a ridiculous way to do aperture synthesis, build the aperture and then select pairs of elements to use. [Richard Q.] Twiss and Little wrote a paper of that kind. [Note added 2014: Twiss, R. Q.; Carter, A. W. L.; Little, A. G. Brightness distribution over some strong radio sources at 1427 Mc/s. Observatory 80, 153, 1960]

Sullivan

Now that’s not what I was going to say. I was going to bring up the Chris Cross…

Bracewell

With its outlying antennas, is that what you were going…?

Sullivan

Yes, right…

Bracewell

But they’re not movable basically.

Sullivan

There not movable but what about the idea of Earth rotation.

Bracewell

Ah, supersynthesis. Now supersynthesis as a word is an invention of Ryle, and for a long time no one could understand what he meant. They thought he’d made some incredible discovery but you couldn’t understand his paper very well. Well, in any case, now that we understand the paper, we see that Christiansen invented supersynthesis and had used it some years before. He just didn’t have the luck to hit on such a felicitous expression. So I would subscribe to the view that observing with a linear array in different position angles on the Sun as the seasons change, that is as the Sun’s declination changes, and as the time of day changes, and combining that with similar observations with a perpendicular array, that is supersynthesis. I prefer to call it Earth rotation synthesis but I think that’s in fact what Chris did.

Sullivan

I don’t quite follow you saying that Ryle’s paper wasn’t understood or his term. Which paper would this be now?

Bracewell

Well I think there was a paper in Nature, which you would be more familiar with than I, in which the word supersynthesis just showed up.

Sullivan

I don’t remember where the word first showed up but I think the paper you are talking about is 1960 or something like that. And you are saying there was some confusion over that, what he really meant.

Bracewell

Yeah, I didn’t understand it.

Sullivan

Was it because everyone understood that the Earth could change position angles but it must be that he is talking about something different and we don’t understand what it is that’s different.

Bracewell

Well, I’d have to read it again to find out what it was that was confusing, but I’ve got a distinct feeling in my mind that I thought he was saying that because the Earth is rotating, and the antenna in five minutes will be in a different part of a space, that it’s as though you had an antenna that occupied all the places that it has moved through in space. And I found that puzzling. Now if I were trying to explain that today I would say, “Here we have a pair of antennas between which we are measuring the coherence and that vector displacement is changing as the Earth rotates.” So I may have misunderstood it, but I’m quite sure at the time from discussions there were others that had difficulty understanding what he was talking about. He obviously understood perfectly well what he was saying. And whether he knew that it was identical to what Christiansen had done and disguised the writing a little bit, that’s a possibility too. Well he was obviously thoroughly familiar with what Christiansen had done, and so I think he must have repackaged the idea with continuity in the Cambridge way of presenting things. So it was the next step beyond aperture synthesis.

Sullivan

OK. Let’s shift to some various projects that you were involved in. For instance, apparently you were involved in a proposal while you were at Berkeley for a spectroheliograph at Stanford. I’m not quite sure how that happened.

Bracewell

Well, I’ll tell you what happened. Otto Struve said Berkeley should get into radio astronomy, observational, and that the galaxy was very important. So he took me up to Lick Observatory and found a very steep hillside pointing toward the southern horizon. And inquired whether something could be constructed on this hill, which could look at Ophiuchus, which he liked very much. And I didn’t like the slope of the hill, so instead I wrote a two or three page letter in some detail describing how the Mills Cross concept and the discrete array of Christiansen could be combined and that this might be an interesting instrument for various purposes. So Struve took that to the Electrical Engineering Department where they had antenna wizards like [J.R.] Whinnery, for instance, and got a reading on it. And apparently they couldn’t find anything wrong with it. It was pretty big by their standards. Well, of course Sam Silver was there too. They thought in terms of antennas of up to about 6 feet in diameter in ones. And here I’m talking about 32, every single one of which is bigger than that. So that sounded to them more like Livermore Labs. So it was given to [Edward] Teller. I got to know Teller a little bit. He came and saw me when he found out I was there. He wanted to find out everything I knew fast. That took him about half an hour. But whenever he saw me again, he would pump me very hard and drain my brain. But this proposal was sent to Teller and he gave it to one of the important engineers whose name escapes me for the moment, who ultimately wrote a report on it with a cost estimate. And I’ve got that somewhere. And he said that everything I was proposing was mechanically quite feasible and it would cost about $5,000. Well he didn’t cost everything. I think the $5,000 listed covered the cost of 32 dishes. So the Electrical Engineering Department, that would represent Sam Silver, decided that they’d make me a job offer. Meanwhile I went and spoke to Tuve and somehow mentioned that Teller had seen this. And he said, "Don’t touch it. The money is stained with blood." That impressed me immensely. I had no idea what that meant. I knew nothing about the atom bomb at that time. But I was very impressed. I recoiled. But as a matter of fact I then went and spent six weeks at Stanford where I already knew some of the people. I gave them a course of lectures during the summer of ’55. And they decided they’d make me a job offer. They must have liked these lectures. And being a private university they were able to move much faster than Berkeley, which is a great administrative giant. And the people at Berkeley never materialized with an offer. As soon as they heard that they had competition, they felt this was more than they could overcome. I think I had some other job floating around too. Yes, as a matter of fact, [Donald] Menzel had a job offer too, now that I come to think of it, at Harvard. But Stanford moved much faster and in those days, it was easy to get on the faculty. These days you have to be a genius. But I got in before the barriers were lowered. They just led you up to the chairman of the department and he looked at you and if you didn’t have two heads you were in.

Sullivan

Well, I’ll discount that statement. But how did this report get to be under Stanford’s auspices? You were doing it all at Berkeley.

Bracewell

Well, you see. At Stanford, [Oswald G.] Mike Villard was the instrumental figure here. He said, "Why don’t you write a proposal for the Air Force, and we’ll see how they like it?" Well, as I have told you, I was very young and naïve. And if someone told me to do something, generally speaking, I did it. So I wrote a proposal and it’s a very good proposal. I believe it’s the first description of what is now known as the Chris Cross. I don’t believe there is any earlier description than that. I wrote this proposal and I sent a copy to Pawsey at the same time. Well it was looked at favorably by the Air Force and it asked for $80,000, which they said, "Fine, you can have it." So when that money became available, I returned to California from Sydney.

Sullivan

So you went back for a period of a year or so?

Bracewell

Well it would be more like three months, at the end of ’55. And during those three months something favorable happened in Washington or Boston, somewhere. So I came back and within a few more months cash actually materialized and I started work.

Sullivan

Which is ’57 now?

Bracewell

It was December ’55 that I started back in Stanford. And by mid ’56 I must have had my cash. But I only had myself, no technicians, no drafting, no machine shop, no nothing.

Sullivan

So we come now to the building of the cross at Stanford, which is then ’56 through, what year was it finally finished?

Bracewell

Well if I could tell you the date of the first Sun map that would fix everything. I believe we have Sun maps in 1960. I’m just picturing in my mind a contour map and I think it says May 1960.

Sullivan

Now this once again seems to be a wholly new venture for you. You had not been in charge of building a large instrument before.

Bracewell

Well, right, correct. I really felt cut adrift when I left Radiophysics because I was accustomed to working with the machine shop, a drawing office, and technicians. I knew how to interact with that sort of person. And if I wanted to know something I knew who to go and see down the hall because Radiophysics was a big place with experts on almost everything that I needed to know about. So I felt very much cut adrift and somewhat on my own. I was with other radio scientists but no one in the microwave field. Anything from about 5 Hz up to about 20 MHz, they knew everything. But I was way out on a limb technically. The only people who knew about microwaves at Stanford were the linear accelerator people, who by some miracle were on the exact same wavelength as I was. In fact, the reason I wound up on 9 cm was that the linear accelerator was at 9 cm and there was the possibility that if I needed a T-junction or something like that of going and scrounging it.

Sullivan

But what was the attraction of this for you?

Bracewell

Well, it didn’t seem any risk. I went on two years leave. The people in Sydney didn’t particularly want to see me take off. And I had found the people at Stanford congenial. I liked the look of the main quadrangle, which was like the quadrangle in Sydney, sandstone arcades. And there were lots of eucalyptus trees and the Pacific Ocean wasn’t very far away. The only thing I didn’t realize was that the water is so cold you can’t swim in it. But there were lots of non-negative aspects. And the year I spent in California had revealed to me that it has a pleasant climate. So there didn’t seem to be any risk entailed. If anything fell through, I could call it quits and there would be no problem. But at the end of two years I had made so much progress and things were really moving along. And I was beginning to feel the personal advantages of being in control of your own destiny. Working for a government lab, you are a cog in a wheel. And when I go back to Radiophyisics labs these days and meet my contemporaries, I see that I might have developed the way they have developed. They are great experts but generally fairly narrow now and extremely obedient. I see now where I got my obedience because I grew up in a slightly military atmosphere in that lab. There was a definite hierarchy. As soon as I came to be a professor I was astounded to find there was no one to tell me what to do. As a matter of fact, at Berkeley when I had to give grades to my students, I went to Struve after I’d figured out all the numerical grades and said, "What letter grades do I give?" And he said, "That’s your responsibility." And I said, "Well, I understand that, but how many As should one give and how many Bs? What is the custom around here?" And he said, "We leave that entirely to you Mr. Bracewell." Well, I just staggered out and took a guess. I’ve always wondered how people decide grades. [Laughter]

Sullivan

So can you tell me what you considered to be the unique aspects of that cross?

Bracewell

At Stanford?

Sullivan

Yes.

Bracewell

Well, I’m not quite sure that there is anything unique about it.

Sullivan

That’s a fair answer. It certainly was much larger than anything of its kind, had more sensitivity. Is that not true?

Bracewell

Well, we have to compare it to the Cross that Christiansen built at the same time. Now he built a 64 element cross at 21 cm. I have a 32 element cross at 9 cm.

Sullivan

What’s the size of the dish in each case?

Bracewell

My dishes are 10 feet. Of course, they are solid aluminum. His dishes are bigger, perhaps 18 feet, I’m not sure, and they’re mesh dishes made in the bent tube and mesh arrangement. That cross is operated by pulling a cable that runs the whole length in a very ingenious way. And mine is operated by rotating drive shafts, which came in during the Industrial Revolution, you know. And all I can say in their favor is that they operated every day for eleven years and never had to be attended to, even if not oiled. They worked very well. So mechanically that turned out to be quite good. And Christiansen’s transmission lines are essentially open wire lines in a kind of guide that surrounds them. And my transmission line is waveguide throughout. Now I did get away with half as many antennas as his. I built the same beam width and he was quite conservative by a factor of 2. He put in 32 extra antennas that were not actually needed. That makes his repeats of the Sun twice as far apart as mine. But my Sun doesn’t repeat until the first one is completed. So I think I might have had a slightly superior confidence when I came to design that. I had been thinking about these things very carefully and I didn’t want to build more than I needed. In particular, I had thought up the T by that time, and I realized that I didn’t need to build all the cross. I could build three quarters of it and it would still work.

Sullivan

This wasn’t appreciated until you saw to this?

Bracewell

Well, Christiansen said in a letter to [Charles] Seeger that I invented the T. Well, if he says that, it means he didn’t, doesn’t it? I was impressed by that letter because Charles showed it to me, and I’ve got a copy of it. It was getting pretty apparent at that time that you didn’t need them. However, although I knew that, holes were being dug to pour concrete and I had to make a decision in a hurry, so I went the conservative way there. And it turned out later on that Swarup did the sensitivity analysis for the T and showed quite clearly that it is much more critical an adjustment. The cross is rather basically a good idea and the T is rather sensitive.

Sullivan

Errors balance out.

Bracewell

Right, well you don’t have the centroid offset. That’s what works in your favor. But as to unique things, the one thing we did that I believe was important and got into the whole mainstream of radio astronomy large antennas was the method of calibrating that array. You see, with a three minute of arc beam, that’s about 1/1000th of a radian, if you are trying to hold phases to, let’s say, 1/10th of that, you working at 1 in 10,000. Now that’s the precision of geodetic survey. Geodetic survey, which is the best we do on the ground, works to 1 part in 104. So just to set those antennas out required some rather careful survey, which is why Chris and I are both expert surveyors now. We know a little bit about surveying. But after you have done the best you can like that, you still have to tweak that thing into the last millimeter. In our case, to the last millimeter in something 100 meters long. That’s 100,000 millimeters and we are working to the millimeter everywhere. That’s kind of a bit hairy. So what I invented was a method of making a twinkling reflection at each feed horn. And I got a fluorescent tube about 4 inches long, just a fluorescent tube you could buy in the shop and mounted it across the mouth of the horn, where just being made of glass, it had no effect whatsoever on the incoming radio waves. But if you turned on the discharge, the electrons there would constitute a conducting path for microwaves. Therefore a signal sent from the center of the cross out through the branching waveguide structure, up to that horn would be reflected and would come back with a modulation, which enabled you to discriminate from all the other much larger standing reflections due to mismatching. And you would know which horn it was coming back to because you would turn on the modulation at that horn. Furthermore you could measure the amplitude at which it came back. So the very first thing we found was that one of our feed horns had a piece of unwanted brass strip in it about three feet long and an inch wide, that had not been removed during fabrication. So we got that out.

Sullivan

So this is the first time a signal had been distributed more or less as a calibration in an array?

Bracewell

Yeah. Christiansen attacked that in another fashion and there is more than one way of doing it. But that way of doing it centrally, starting from indoors and getting your reading indoors, just pressing a button to determine which antenna you are going to look at, was quite a step forward. The other thing that was of a pioneering nature about that antenna is the fact that it was the first radio telescope to produce its output in publishable form. We just tore the stuff off and sent it in for publication, month after month for eleven years all told.

Sullivan

To the solar…

Bracewell

Well it went to various places…

Sullivan

What was it called?

Bracewell

Mostly we worked through Boulder under their assorted initials which have changed several times and it came out in their monthly bulletins. The very first time we got that going, computers didn’t really exist, but we had a Flexowriter, which could be operated by punch tape. And Flexowriter was controlled by the antenna so that it moved, carried, shifted, and the carriage return operated and came to the next line. And everything was correctly spaced despite of the fact that typewriters have ten characters to the inch this way and 6 lines to the inch the other way. In spite of all that we managed to produce something that could be…

Sullivan

I remember it was arrays of digit on a circle. Wasn’t that the way it was given?

Bracewell

Yes. And, over the course of time, we improved that as things came along. After a while we abolished their analog computer, which computed hour angle and computed them and made punched cards and then used a deck of punch cards to control the thing. And then more recently it was elaborated even more. The whole eleven years of that was duly published, which is more than can be said for any other radio telescope.

Sullivan

That’s true in many cases.

Bracewell

And the whole of the eleven years is available in uniform format throughout, in machine readable form on tape or cards. I can’t tell you the number to write for to get it in Boulder.

Sullivan

Was the purpose of the instrument from the beginning primarily as a monitoring instrument, to do a couple of experiments with it, but mainly to serve as a monitoring instrument.

Bracewell

Well, I hoped that it would do a variety of things. And we did publish a range of things. For instance, we discovered the central component of Centaurus was double.

Sullivan

That’s with Little in ’61, the AAS abstract here? [Little, A.G.; Bracewell, R.N. The Central Component of Centaurus A. AJ 66, 290, 1961]

Bracewell

Now there was a suspicion that it was double as a result of work that Little had done before he came to spend a year with us. But we looked at five or six of the brightest sources and found out a little something about all of them. But the instrument did not have the sensitivity to go into a second order of investigation. For instance, with a 3 minute beam you can map Cassiopeia but there are not very many elements. And after you’ve mapped Cassiopeia and Taurus, there are no other sources accessible to the instrument. There’s just not enough collecting area. We also added outrigger antennas and got down to 50 seconds of arc, which for a time, I think, probably held the record for resolution of any radio telescope. I know that there is no radio telescope even to this day that can make Sun maps of the kind that we made. There is no 100 meter, 10 cm dish that can make some maps on a day to day basis. Of course at Bonn they can make an occasional Sun map which is comparable.

Sullivan

There is nothing that is devoted to it in any sense. Let me got back to 1958 at the Paris Symposium. Of course you edited the proceedings of that meeting. It seems to me that was a rather interesting and perhaps critical meeting in the history of radio astronomy. What thoughts do you have on that?

Bracewell

Yes. Well it was a great meeting and it was probably the last meeting at which all the radio astronomers could talk to one another and cross the boundaries from topic to topic. Since then, of course, there have been many radio astronomy sessions with radio astronomers presence but with a tendency to emphasize instrumental aspects. The Paris Symposium was definitely of the scientific kind. No undue emphasis on instruments. It was truly scientific.

Sullivan

Do you have any particular memories of sessions or papers there?

Bracewell

Well I do remember that it was agreed that all the discussion would be published. And consequently some careful organizing was required. And as the person entrusted with editing the thing, I saw that I had better be the person that got the discussion. My experience with organizing the URSI assembly in Sydney stood me in good stead here. So I had people posted at the four corners of the room with slips of paper. Something you’ve seen…

Sullivan

That’s probably the first time that was done. It’s almost always…

Bracewell

Well, I couldn’t claim to have invented it. It’s often done now because it works. And I appointed a whole group of people right there at the meeting. I had found out how to appoint people. You just go up to them and you say, “Between 2pm and 5pm, you will be in charge of collecting the pieces of paper that will be handed to you by four people who will appear mysteriously in the room.” I would make the four appear, you see. I would say to them, “All you’ve got to do is stand in the corner.” But I told this one other guy, “You’ve got to collect all those pieces of paper. And furthermore, you’ve got to spend the rest of that night chasing down the guys who didn’t give their pieces of paper in. And I don’t want to see you until you’ve got every paper from that session. And then I want the lot on the last day. And there will be no opportunity to add or subtract.” And if you appoint enough people – of course, if the fellow says, ‘I won’t do it,” you get someone else. It’s really very simple. They always say they’ll do it. Some are better than others.

Sullivan

Were there recordings also?

Bracewell

No. I have all those slips of paper, the manuscript writing of the people, many of whom are no longer with us. [Note added 2014: The discussion slips are now with the Bracewell papers in the NRAO Archives.] So if you find an interesting quote in the book and you would like to have the piece of paper and frame it…

Sullivan

I might just take you up on that. Do you remember if there was much editing for whatever reason?

Bracewell

The editing was incredible.

Sullivan

No, I mean of these remarks.

Bracewell

Well, in a few cases I think I might have recirculated that discussion because it clashes.

Sullivan

It didn’t make sense or…

Bracewell

Well, people stand up and say something, then they hear what the other man says and then they write down what they would have said. And consequently when you get these two pieces of paper they just don’t make sense. But my feeling was that we didn’t need a verbal record of exactly what was said. The purpose of the discussion, of course, was to illuminate what was said. So if people wanted to change it we just updated it as much as possible.

Sullivan

Another interesting paper of yours I’d like to ask you about is the one in 1960 in Nature on extraterrestrial communication [Note added 2014: Bracewell, R.N. Communications from superior galactic communities. Nature, 186, 670, 1960], which I think may be number two after Morrison and Cocconi. [Note added 2014: Cocconi, Giuseppe; Morrison, Philip. Searching for Interstellar Communications. Nature 184, 844, 1959] It’s certainly amongst the first few. Were you basically inspired by Morrison and Cocconi to do this?

Bracewell

Yes.

Sullivan

Or had you been thinking about these issues beforehand?

Bracewell

I don’t recall that. All I recall is that I read their paper and began talking to people about these fascinating thoughts. And I thought that was a pretty good paper. I found out a few things. I discovered that there is a relationship between how far away the nearest community is and how long they’re likely to survive. And that idea has been so difficult to grasp that people reading the paper generally haven’t noticed that. Everybody who read it notices that there is a reference to Van der Pol and long delay echoes. But the discovery that distance to the nearest advance community is connected to the average longevity is a very striking result. And it slowly filtered into the literature, which is now quite extensive. But it was there all the time.

Sullivan

Did you feel any social pressure that maybe you really shouldn’t publish this sort of thing? You know that this was going out on a real limb.

Bracewell

People, strange to say have asked me that from time to time. No, I didn’t.

Sullivan

It seemed to you like a perfectly acceptable topic for Nature?

Bracewell

Yes, but some people reading it obviously thought they wouldn’t have published it. There are a number of people who conveyed that impression to me. No, it seemed to me that it was a perfectly bone fide topic. But no, I must tell you that I had had some previous contact with this because I was in Berkeley with Su Shu Huang in 1954 and this is six years later. Now, Su Shu had written papers on the habitable zone so I already knew this was a reputable subject. And Struve was there, and he had been very interested, and later encouraged Frank Drake in what he was doing with Project Ozma. And I went to Green Bank when Struve was Director there, probably in 1960, and gave a talk on my Nature paper. And I know Frank Drake and [Sebastian] Von Hoerner were there, and I don’t know who else. So I guess that this didn’t come out of a clear blue sky but clearly the Cocconi-Morrison paper stimulated my paper.

Sullivan

Just a couple more questions here. You took a tour of the Soviet Union in ’61, I believe,or just before then. You reported on it in Sky and Telescope. [Note added 2014: Swenson, G.W., Jr.; Bracewell, R.N. Some Russian radio telescopes. Sky & Tel. 22, 77, 1961] What was your impression of radio astronomy in the Soviet Union at that time?

Bracewell

Well, we visited the enormous structure that [Viktor] Vitkevich had going at the time, which was never completed, huge towers and a great cylinder which could be tilted. A great idea. Why it slowed down and never produced, I’m just not up to date on. But the Vitkevich unfortunately died and he wasn’t regarded as very important by the other Russian radio astronomers. So perhaps he ran into some funding problem. We also saw the great 20 or 25 meter millimeter wave dish at Serpukhov, very interesting mechanical thing. It looked something like the interior of a submarine. It was obviously built by naval engineers. I’m not sure I’m right about that. It was technically very interesting. And George Swenson, of course, was mechanically inclined…

Sullivan

He was with you on this trip?

Bracewell

The two of us went together. He thought of it as a matter of fact. And we spoke to the engineer, whose name escapes me for the moment, which it shouldn’t, and he spoke German and Russian. And I could read German, but if they spoke it at me fast, it wasn’t too good. And I certainly didn’t know the German words for gear teeth, things like that. As a matter of fact, I think I do know that but I think I know what a (Verzahnungen?) is. But in any case, there were lots of technical words, mechanical terms I certainly wouldn’t know the German for. So we had very interesting exercise in communication. And when they tell you in the university that there are three modes of communication: writing, speaking, and drawing, we don’t pay much attention to drawing. But, by golly, when the other two close down, drawing is most helpful. So we had lots of good discussions, found out a lot of things. Then we went and saw the fantastic installation at Leningrad and Pulkovo with all the multiple plane mirrors, which we thought was crazy. And when they built an even bigger one, RATAN, more recently, I thought that was even crazier. So I was very impressed by the magnitude of the mechanically undertakings. But on the whole, we thought the Russian were stronger on giant mechanical things than they were at the underlying science. On the other hand we went and visited [Josef S.] Shklovskii and [Vitaly L.] Ginzburg and these people were right at the heart of the theoretical side. But they were quite disconnected from these other people who obviously had large sums of money. I never really understood the funding situation there.

Sullivan

I would agree with you. What do you think it is that the Russian don’t come out with any useful data from their instruments?

Bracewell

I think that they have several places running in parallel. It’s a much bigger country than Australia, which can only afford to do one thing. And if astronomy isn’t competing very well with botany, well they’ll cut astronomy. But in the Soviet Union they can have many projects going in one and the same field, and clearly all these places somewhat independent, some of them totally independent. They fed back to the government through channels had no relationships at all. And they’d managed in different locations for various reasons to start a whole lot of project and they were very diverse in their quality. Some were just not really very inspired but they’d managed to, locally at least, get the financial support. Others were very good, just all over the shop as you might expect.

End of Tape 132A

Begin Tape 132B

Sullivan

So you were saying that the situation that you saw in the Soviet Union in 1961 is not unlike what was in the U.S. 10 or 15 years ago?

Bracewell

Yes, we had dozens and dozens of radio astronomy projects, all supported in diverse ways and of varying merit.

Sullivan

It just wasn’t efficient use of funds.

Bracewell

I wouldn’t like to argue about the efficiency or not because if you have a program that doesn’t seem to be as good as what is going on at the University of Michigan, is that inefficient? You’ve got no way of saying what’s happening in Florida and how that will feed into other values in the country. There is no one wise enough to say.

Sullivan

No but, of course, you can’t do everything. You have to make decisions.

Bracewell

Well, it depends on who makes the decision. You see, if the local chamber of commerce will fund a radio astronomy venture in Florida, that sort decision doesn’t arise.

Sullivan

But that wasn’t really the case in the U.S. 10 or 15 years ago. It was ONR [Office of Naval Research] and NSF [National Science Foundation] pretty much.

Bracewell

And about six others at least.

Sullivan

Oh really?

Bracewell

Well let’s start naming them: the Carnegie Foundation, the Ford Foundation gave out lots of money including giving money to Australia…

Sullivan

Well I know that but did they actually fund anyone in the U.S.?

Bracewell

I suppose so. I wouldn’t care to say. There is the Army Signal Corps.

Sullivan

Who did they fund?

Bracewell

Well I’m just talking about 10 or 15 years ago.

Sullivan

Yeah but who did they fund?

Bracewell

Well, they got the first Moon echoes.

Sullivan

That’s ’46 now. They didn’t stay in the game.

Bracewell

Yes they did. You could still apply to the Signal Corps for cash for all sorts of assorted things. I’m sure you’ll find there are some radio astronomers getting money from there. There was, of course, the Air Force Office of Scientific Research. But there were also the Air Force Cambridge Research Labs [AFCRL]. Now you could also get money from Sacramento Peak, which got its money from AFCRL but nevertheless it was a quite different procedure. Now if I had to scratch my head… and there was the Research Corporation. I got money from them myself. So did Reber.

Sullivan

Reber still does.

Bracewell

Now we are up to at least six or seven and I’m sure there were 12 or 15 if you went and counted them.

Sullivan

In 1962 was published your review article on radio astronomy techniques in the Handbuch. [Bracewell, R.N. Radio astronomy techniques. Handbuch der Physik 54, 42, 1962.]

Bracewell

That was my best selling reprint. I blackmailed those chaps, they were three years late printing that. They got my article in on the deadline and then they waited for another several years until the other articles came in. So I blackmailed them, and the result was that I got 500 free reprints. It’s a thick reprint. It’s a book.

Sullivan

Do you still have it?

Bracewell

Do I still have any?

Sullivan

Yes.

Bracewell

I may have one.

Sullivan

I’d love to have one if you have a spare.

Bracewell

Each year from Manchester, I would get applications, individual hand-written letters from about 15 research students who wanted one. And I’ve sent them everywhere.

Sullivan

But I wanted to ask you, it brings up the question of techniques in radio astronomy and so forth. And another theme I would like to look into in my overall study is the relationship between the technology and the science. How do you see that relationship? Do you think that it is sort of a willy nilly thing, whatever could be done did get done…

Bracewell

No, I’ve got quite a systematic view on that, which is shared by lots of people. For instance, there was a committee which Jesse Greenstein chaired that brought out a report on astronomy. And in that, it points out that there are two ways of going about astronomical research.

Sullivan

This is the 1970 committee?

Bracewell

That sounds about right. I’m just thinking of the National Academy of Sciences’ Newsletter. No, I’m thinking about their buff colored 4 or 6 page newsletter that comes out every now and again. And I remember it had an excerpt from the Greenstein Report reproducing this material. I’m now going to have to paraphrase for you. There are two things you can do: One is to sit down and theorize about what might be there and then design observations, a crucial experiment perhaps, to decide if this is the case or not. The other thing you can do is look at what phase space has been explored by instruments, what bandwidths, what frequency coverage, what wavelength, whatever. And then imagine an instrument which would explore things which would not have been observed by existing instruments. Now you build that instrument, and in the expectation that you will discover something. There are two different modes of going about it. Now there are people who do not know about the other mode. And you discover the existence of these people in reviews of your proposals that you get back from NSF, where someone will say, “This man hasn’t said what he’s going to discover.” So you realized that there are people who are unaware of and certainly don’t subscribe to this other way of doing it. Now the Greenstein Report says that 90% of all discoveries in astronomy have been made by building a new instrument regardless or in the absence of an idea of what you will discover. Now that is astounding news to a lot of people. I believe it because I’ve seen all through my life both in ionospheric and in radio astronomy and some other things I’ve had experience with, that’s been inevitably the case. You push the instrument beyond what you had before, and nature will provide you with occupancy of that new space you are observing. If you expand your instrument to observe polarization, you will discover polarization. It will be a discovery because it was not measureable when the instrument that did not have polarization.

Sullivan

So you have a philosophy that nature will take up all these degrees of freedom that are possible in essence?

Bracewell

I’m persuaded to that by experience. I’ve applied this once or twice. When the 3k radiation was discovered it was reported as isotropic. Well, of course it was 3 ± 1 degrees. I said to myself, either this is going to be a new branch of science or not. If it proves to be perfectly isotropic then there is only one number to measure. When that’s been measured, and of course, as a function of frequency, that will be the end. If it is to be a new branch of science then there will be structure to be observed on the sky. So I began to imagine what the structure might be. I thought you might see a lacy network. You might see cracks between the parts of the universe as it broke up, or you might find three great lumps.

No one would ever do the theory of a universe that broke up into three lumps. They will do the theory of an isotropic universe, or they will do the theory of a universe with homogenous turbulence, that’s to say with an infinite number of things. Something that’s Gaussian, that sounds like a good theory. Or they might do something with a dipole or a quadrupole moment. But if the universe broke up into something like a pyramid with four points, no one would ever do the theory of that. That is the sort of thing one discovers. And if you were to look at the sky and find there were three great big lumps there with cracks running between them, everyone would say, "Great." Then they’d do the correct theory.

Sullivan

And say, "We should have known it all along."

Bracewell

Alright. So I said, "Let’s have a go at this." So we did two things. I had one 60 foot dish and I thought of a very ingenious instrument that could be put at the focus, and look for variation from three degrees. So we did that. Ned Conklin had just joined me as a young student and he did the observations. And he hated to do it because for the first few weeks he couldn’t see anything. And I kept telling him, "Ned, this has got too much thermal instability here." So we’d bring all the equipment inside and we turned lamps on at hourly intervals during the night. We’d turn the lamp on for an hour and then turn it off. Then we’d look at the record to see if this modulation got through. So gradually this instrument became more and more stable. But still we didn’t see anything. It was a null experiment. Well some of the best experiments are null experiments. The outcome of that was that we were able to show that 3 millidegrees, 3 milliKelvins, I’d never heard of a milliKelvins, 3 milliKelvins was the biggest that the departure could be from isotropy in the strip of sky that we observed. For some years nobody could beat that. And it hasn’t been beaten by much now. But it’s been quite impressive how much it fit into cosmology. All sorts of people use it. The next thing we did was to say, "Well, that was too bad. We didn’t find all these cracks and things. That was too bad. But let’s have a look for the absolute velocity of the Earth through the cosmic sea of photons." And we were the first to find what is now known as the great cosine in the sky with an amplitude of about 3 milliK, about the same as before, about 1 part in 1,000.

Sullivan

About 300 kilometers a second.

Bracewell

About.

Sullivan

With what kind of reliability?

Bracewell

Well we don’t know what the plus or minus would be on that. It’s probably 20% or so, you see. But we do know now because it’s been confirmed. Now the history of that is kind of interesting. That was done about 1968, I suppose, more than ten years ago. And the outcome was that we measured the velocity component parallel to the Earth’s equator. We did not measure the component parallel to the Earth’s axis because we used the rotation of the Earth to do it. Now the instrument was very clever. It consists of a pair of electromagnetic horns inclined about 45 degrees to the vertical, comparing what’s happening in the east with what’s happening in the west. And at intervals of a few minutes we interchanged the two horns. Now the horns are made as identical as possible. The T junction between them is made absolutely symmetrical and tested and reversed and all sorts of things done to it. And then on top of that we’d just rotate the whole set up. Well that proved to be a very clever thing to do and revealed this sinusoid. It also revealed a bump where the Galaxy went overhead. And so for that reason, but really more for another reason, I wasn’t sure that this result was right. The other reason is, suppose there is a gradient of temperature in the atmosphere, suppose when you look towards the east it’s hotter than when you look towards the west, which it might well be. We were on top of a mountain at 14,000 feet but nevertheless there is a sea in one direction and the continent in the other direction. Now supposed there is 3 millidegrees resulting from that. Oh, boy, you see. You’d have to repeat this on the other coast. So we didn’t advertise that much. That was duly published in Nature [Conklin, E.K. Nature 222, 971, 1969] and Ned Conklin reported on it at an IAU Symposium in Stockholm and that was duly written up and of course that’s available in his thesis. But we did not go around shrieking that we’d discovered the absolute velocity of the Earth. However, about seven or eight years later, with vastly improved instrumentation, Berkeley using U2s and Princeton using balloons repeated this. And in right ascension and in velocity they bracket us. Our result agreed better with Princeton than Berkeley agreed with Princeton. And we agreed better with Berkeley than Princeton agreed with Berkeley. Neither of those chaps, they’re about two standard deviations apart, and we agreed within one standard deviation with both of them. So I’m convinced now that that was the first detection and a reasonably accurate measurement of the absolute velocity of the Earth. Whether it’s with respect to what, I don’t know but there it is.

Sullivan

But you bring this up as an example of just do it, and see what’s out there…

Bracewell

Absolutely right, there’s something there.

Sullivan

One final thing is I’d like to hear your version briefly of the famous polarization of Centaurus A on the 210 foot story.

Bracewell

Well we had been observing…

Sullivan

Who is we now?

Bracewell

Now who would we be? There is a paper of which the authors are Cudaback, Little, and Bracewell. [Little, A.G.; Cudaback, D.D.; Bracewell, R.N. Structure of the Central Component of Centaurus A. Proc. Natl. Acad. Sci. 52, 690, 1964] That’s David Cudaback, now at Berkeley. [Alec] Little you know. We wrote a paper based on observation with the east-west arm of the solar cross at Stanford. And we measured the separation of the components of Centaurus A at 5 minutes of arc. That would be a precision measurement, about 5.0. It was a precise value. And we also knew that those two components were of different widths, a couple of minutes of arc in one case and one minute of arc and I forget the decimals, in the other case, but distinctly different and of distinctly different central intensities, not so very different in flux density. So it was very hard information. We knew which one was which. Now I had that information with me when I went to Parkes, and the resolving power of the Parkes dish with the receiver which was then available at 10 cm was about 5 minutes of arc. The beam width – you’d have to check this – was about 5 minutes.

Sullivan

No, that’d right.

Bracewell

So at first sight it doesn’t sound as though you can do this. You’ve got two things 5 minutes apart. But, we also knew from looking at the picture of Centaurus A that these components were not likely to be on an east-west line but were going to be either up and down on this diagonal or on the other diagonal. We didn’t know which but from the symmetry of the gadget you could see it would surely be one or the other. So I knew that was going to be some diagonal thing here. Trouble with the way the dish was set up, if you did ordinary TV type scans they were not compatible. You do one scan and the next scan had a zero error that was not right. So as soon as I found that I said, "What we’ll do is this. We will do an unusual thing. We’ll scan diagonally. We’ll get both drive motors going together and we will scan up the diagonals, so we will go through one source and then through the other on the same scan, so we won’t have this loss of time while all this happened you see." Now the facility for rotating the horn had just been installed. And as you will of heard, I was the first person to make good use of that ability which that instrument had. However I was a bone fide guest observer and the facility was there; so naturally I wanted to turn this knob. So I took laborious scans on three nights doing this work entirely on my own. All this observation was done with only myself and the man who drove the telescope. They wouldn’t let you touch it there. And Tom Cousins, who was down in the next floor, controlling the receiver which was still a bit sensitive. He had built it but he made sure the gain stayed constant, watching a monitoring meter and so on. So I scanned up this thing and did these diagonal scans. And because of hysteresis in the drive, I had to scan horizontally, turn on the north-south drive. It would go up this way. Turn the north-south drive off and go that way. Then back up. And then determined what the hysteresis would do, I did staggered diagonal scans like that. They were a very unusual thing, never been done since. But it was just what was needed to go through these two components in quick succession and see what was happening to the polarization. So immediately I’ve got 15% polarization. Now that was staggering because for years I’d been watching what Connie Mayer did measuring 1% polarization in this, and the half polarization in that. And polarization had become a very tedious thing which one didn’t want to launch into lightly. And all of a sudden we discover that if you’ve got the resolving power, you’ve got the polarization. It revolutionized polarization. So that’s the story of what happened.

Sullivan

Anything else you feel should be covered up through ’62 or…

Bracewell

That’s the whole story of my life.

Sullivan

The whole story. Thank you very much.

End of Interview

Citation

Papers of Woodruff T. Sullivan III, “Interview with Ronald N. Bracewell ,” NRAO Archives, accessed January 17, 2021, https://www.nrao.edu/archives/items/show/908.