Interview with O. Bruce Slee
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The interview listed below was originally transcribed as part of Sullivan's research for his book, Cosmic Noise: A History of Early Radio Astronomy (Cambridge University Press, 2009). The original transcription was read and edited for clarity by Sullivan, retyped to digitize in 2016, then reviewed, edited/corrected, and posted to the Web in 2016 by Ellen N. Bouton. Places where we are uncertain about what was said are indicated with parentheses and question mark (?).
We are grateful for the 2011 Herbert C. Pollock Award from Dudley Observatory which funded digitization of the original cassette tapes, and for a 2012 grant from American Institute of Physics, Center for the History of Physics, which funded the work of posting these interviews to the Web. Please bear in mind that: 1) This material is a transcript of the spoken word rather than a literary product; 2) An interview must be read with the awareness that different people's memories about an event will often differ, and that memories can change with time for many reasons including subsequent experiences, interactions with others, and one's feelings about an event.
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Begin Tape 86A
Sullivan
This is talking with Bruce Slee on 1 March 1978 at Radiophysics in Sydney. Could you please tell me about, you said you were a radar operator in the War, and -
Slee
Yes, well, I was a radar mechanic in the War. I was stationed at a radar station in Darwin. One day in, oh – I think it was October or November, 1945 -
Sullivan
Just after the War was over.
Slee
Yes, just after the World War was over. We picked up strong signals from the direction of the sun as the sun was setting. I thought this was strange at the time, but I remembered that I’d seen some report that Radiophysics was interested in this kind of research. So I immediately sat down and wrote a report on what I’d seen, and sent it to Dr. Pawsey. And he wrote back and expressed quite a bit of interest in what I thought was a discovery. He set up an appointment later on to meet and (?) I was discharged; from then on, he offered me a job as a technical assistant at radio physics and -
Sullivan
I see.
Slee
That’s how I came to join the staff.
Sullivan
And that was 1946 when you joined the staff?
Slee
Yes, it was November, 1946 at (?) Cross.
Sullivan
Did you ever do any more observation on the sun with that radar on -
Slee
No, this was the only time. It was really active; the sun lies -
Sullivan
What frequency was that?
Slee
This was at 200 megahertz.
Sullivan
And I asked you before, but you don’t remember of any report circulating through from the New Zealand or Australian military at that time of solar interference?
Slee
No, the only report I’d seen was originated in Radiophysics, I think. It had been distributed around the radar stations.
Sullivan
But this was at the end of the War though?
Slee
Yes.
Sullivan
So you hadn’t seen Hey’s report?
Slee
No. I hadn’t at that stage.
Sullivan
That came out in 1942?
Slee
Right.
Sullivan
Okay. So you got here in 1946 at Radiophysics and what did you find?
Slee
Well, I found quite an intense activity and excitement; everybody was mainly in the solar field at that time: Ruby Payne-Scott, Dr. Pawsey, Lindsay McCready, John Bolton, Gordon Stanley, and I think Paul Wild had just arrived on the scene. Everybody was working at that time on solar research. They had stations over at George’s Heights on the harbor and one at Dover Heights. And the first two or three months or so, I was working with Ruby Payne-Scott, and Don Yabsley out of George’s Heights on solar, mainly technical field, getting receivers going and not doing much analysis.
Sullivan
Right. You were not trained as a scientist per se.
Slee
No, no. I was not trained at all. I was more interested in the engineering side when I came into it, the technical side. But at the same time, I began in 1947, the beginning to do a radio engineering diploma at Sydney Technical College and I continued there for five or six years.
Sullivan
Part time?
Slee
Yes. All this time, of course, I was a technical assistant and mainly was interested in keeping receivers going and repairing aerials and doing some observations, too. Quite a lot of observations at the time there. Early in 1947, about March or April I think, I went out and joined John Bolton and Gordon Stanley at Dover Heights; and from then on, I was mainly concerned with extra-terrestrial work on sources. They had, at this stage, just discovered the radiation from the discreet source in Cygnus; and they were busy doing experiments with sea interferometers up and down the coast, going to higher and higher cliffs, trying to get better and better resolution and mainly on Cygnus-A to try and locate its position and (?)
Sullivan
Right. How many different locations were there actually?
Slee
I think they tried at Dover Heights, of course, but there was only a 200-ft cliff from there and it meant a long reef, which was 300-400 ft. high. At Palm Beach, I think they tried there, and then late in 1947, they went across to New Zealand and they got a 1,000-ft high cliffs on both the east and west coasts of New Zealand.
Sullivan
I see. So they were much higher there.
Slee
Yes. And it was here that they located the source quite accurately and (?)
Sullivan
You didn’t go on that trip?
Slee
No, I stayed at Dover Heights and did some, carried on experiments we were doing at the time. We had some simultaneous work between here and New Zealand at the time. It was one of the first spaced-aerial experiments on Cygnus-A; and of course, we were interested in the time and intensity fluctuations of Cygnus-A, whether they were inherent in the source or ionospheric. And of course, we found that they were not correlated to (?)
Sullivan
Did that result come out pretty quickly once you began this analysis with, there was never really much doubt in your mind?
Slee
Oh, yes. It was quite (?) so after they returned from New Zealand, we were, the analysis had been completed and we were quite sure that it was ionospheric scintillation.
Sullivan
That’s interesting. This is 1947?
Slee
Yes, the end of 1947, early 1948.
Sullivan
And of course, you didn’t publish this until 1950 – this paper we’ve been looking at, Stanley and Slee.
Slee
Yes.
Sullivan
And yet, in the traditional history of this sort of thing, the two papers published in Nature by, who was it now, Lovell and Smith and then someone else, anyway -
Slee
(?) signals from Cygnus source.
Sullivan
Right, but I mean as far as establishing the ionospheric origin. There are a pair of papers in Nature in 1950 – one of the rare cooperations between Jodrell and Cambridge in which they did the same thing that you’re talking about, with a smaller baseline. And that’s usually given the credit for having established this, but you’re saying that three years before you -
Slee
Well, two years anyway.
Sullivan
You were pretty convinced that it was that way, but you didn’t publish it right away.
Slee
We were quite sure at the time, yes.
Sullivan
Do you remember particularly why?
Slee
I don’t know. I guess we didn’t consider it particularly important perhaps.
Sullivan
Well, in retrospect -
Slee
Yes, it does turn out. But it could have been -
Sullivan
Seems to be rather important.
Slee
(?) as important, yes.
Sullivan
But it didn’t seem, I’ll have to ask John Bolton that, also.
Slee
Of course, we continued on actually doing ionospheric work on scintillations from then on for several years and getting the seasonal and (diurnal?) characteristics of scintillation activity.
Sullivan
Right. I’m just puzzled why you didn’t just send a letter off to Nature about the main results.
Slee
It is rather strange. We would these days I’m sure.
Sullivan
Is it fair to say that Gordon Stanley was also at this time in a similar sort of job as you?
Slee
Well, he was rather higher up the scale; he was a technical officer and he’d finished his diploma at the City Technical College. Once you finished your diploma, you usually became a technical officer.
Sullivan
I see. And then John Bolton would be a research officer? Is that the right terminology?
Slee
He was a research officer at that stage, yes.
Sullivan
I see. Okay. Well, the first publication that you’re involved with is the famous Bolton, Stanley and Slee in Nature in which you suggest the identifications for Taurus, Virgo, and Centaurus-A. If you could tell me how this came about, and how you got hooked into the optical side. I’d be interested.
Slee
That came about as a result of the trip to New Zealand, really, because they also observed Taurus and Virgo and Centaurus as well as Cygnus over there and were able to locate the position of the source much more accurately than they could at Dover Heights.
Sullivan
Basically, because of the much higher cliff?
Slee
Yes, because of the higher resolution. And well, I just looked up the sky atlases and found that the position (?) had an accuracy of a few minutes of arc.
Sullivan
Like 8’ to 10’ or so.
Slee
Yes, and the galaxies happened to be located within error box and I suggested, we suggested these as optical identifications. (?) fairly unusual looking objects. I think that was about the only reason to say that, at the time, were possibly associated with radio source.
Sullivan
M87, of course, is not that unusual at a long exposure. It looks just like a normal elliptical galaxy, but it is a bright one – no doubt about that. The, were you in contact with, I’ve heard Harley Wood was leading you on to some of this optical information. Were you involved in any of that yourself?
Slee
No, I’m not really in touch.
Sullivan
John Bolton and mainly that would be talking to him?
Slee
I, really came in on that paper because I said, the equipment mainly on some of the analysis, but none of the interpretation at that stage would have been due to me.
Sullivan
Right. And were you involved at all in the corrections for refraction for the positions and all that?
Slee
Well, no, I didn’t really do much of that. John did most of that.
Sullivan
Okay. I’ll check with him. Because, as you know, there were some that didn’t turn out to be quite in the right position because I guess, in retrospect the -
Slee
I think Cygnus itself.
Sullivan
Right.
Slee
(?) to identify Cygnus with galaxy (?)
Sullivan
Since your main contribution at that time was with the receiver, let’s just look at this Stanley and Slee paper and in Section two you talk about receiver problems having to do with receiver stability and interference. You state that you almost had to observe in the wee hours of the morning. And even then, I guess, it was not ideal.
Slee
No, of course we had to use total power at that stage.
Sullivan
Well, you talk about the Dicke system here and you say that it’s (?) sensitivity. For some reason you weren’t willing to use it at that stage. Was that (?)
Slee
We had a pretty crude mechanical switch from the Dicke system; we didn’t have the electronic switching at that stage.
Sullivan
You didn’t actually use it, I don’t think. But you consider it here in this paper, that’s what I’m saying. So that was the main trouble with the switch?
Slee
Yes, power and mechanical difficulties with the switch that prohibited its use. It was generally inferior to the (?) system.
Sullivan
I see. Was this going to be switching in and out a disk of some kind?
Slee
Yes, that’s right.
Sullivan
But, in fact, the Dicke system was, of course, set up for microwaves primarily. Were there any differences that you had if you were going to use it at something like 100 or 200 megahertz? Would it work just as well?
Slee
Well, of course, we had to find some way of balancing the switching between a pretty hot sky and couldn’t use cold waves, so you had to have a hot wave (?)
Sullivan
Okay.
Slee
Bounce it against (?) keeping the hot lead stable.
Sullivan
That’s true. And of course, there’s less motivation to use a Dicke switch because of the signals are stronger basically – you’re not as subject to gain fluctuations. It’s not as critical a problem. Would you agree with that?
Slee
You’re limited more by the receiver, the noise background (?) receiver noise temperature, of course. There’s not that great an incentive to use the Dicke switch, really.
Sullivan
Let’s see what else you discussed in this paper. Well, one question that came to mind as I looked at this paper last night is, why did you not got to a more remote site to get rid of the interference problem?
Slee
I should think probably because of financial difficulties. Setting up a station outside well Sydney on a cliff somewhere probably would have been pretty expensive in those days to run.
Sullivan
Certainly not as convenient also. But it seems like -
Slee
I certainly wouldn’t have been able to get there (?)
Sullivan
Okay. Well, looking at this list of sources, there are 22 altogether, and they range down to 200 Janskys, as we say today, in intensity. Was this based on a complete sky survey? How were you sweeping the sky, so to speak? Did you try to do this in a methodical way?
Slee
Oh, well we’d leave the aerial fixed on the (well?) north and leave it there for a couple of nights. Then swing the beam further around the horizon and do another long run, just look for the interference patterns on the source, on the records.
Sullivan
Could you leave it unattended through the night or did you always -
Slee
We would usually be there; somebody used to be there. It was quite exciting in those days. You could expect to find a new source most every night.
Sullivan
You did it. And say twice, just for confirmation?
Slee
Confirmation, yes. You had to wait six months to get the data on a section of the sky, of course.
Sullivan
So you could get it in the wee-hours of the morning, you mean.
Slee
Yes, that’s right.
Sullivan
There’s another interesting column in this table; that’s the number of observations, where for Cygnus you have 320.
Slee
Yes, well, for those major sources, we looked at them almost as often as we could and we’d turn the aerials around just for a quarter of an hour or so each day just to look at them and then go back to the surveying.
Sullivan
And for the others, it’s more like ten or twenty typically. Still that’s one hell of a lot of observing going into this list.
Slee
We were interested mainly in the scintillation activity. Some of the records stronger, four or five stronger sources.
Sullivan
Right. Was the equipment such that, what I’m trying to get at is what fraction of the time did it operate? Was it breaking down a lot?
Slee
No, it was pretty reliable on the whole. We had a lot of blackouts in those days, which was one of the main troubles. After the War, we had a lot of coal shortages and strikes – for several years there, we often had blackouts.
Sullivan
You didn’t have your own generator?
Slee
No.
Sullivan
Once again, was that just a financial problem?
Slee
I don’t know why we didn’t go in for a generator. We could have quite easily; there wasn’t much power being consumed. But the equipment was pretty reliable and pretty simple, too. Just a straight superheterodyne with stabilized power supplies chart recorder, DC amplifier, chart recorder. And the aerials were rather simple things to, not much to go wrong with them. But normally we used to be, there used to be somebody out there most of the night in case there was a power failure and thing had to be reset.
Sullivan
And here’s another part of the paper where you talk about temporary sources, which may be a temporary source, interesting terminology – meaning time variable, I guess. That must have been pretty hard to ascertain. I mean the intensities that you got were probably trickier than the positions and the sizes, were they not? Or is that true? Getting accurate –
Slee
Yes, they were. Of course, you’re subject to typical interference patterns – to refraction which often adds scintillation which was quite severe at the low frequencies and it was rather difficult to estimate the fringe amplitudes on many occasions. For instance, on this kind of record, it would be pretty difficult.
Sullivan
What were you using as your basic calibration source?
Slee
Noise diodes, absolute calibration standard at that time.
Sullivan
And were you trying to calibrate the other sources versus one like Cygnus or Taurus?
Slee
No, we didn’t attempt to use sources themselves as a known (?) We relied exclusively on the noise diode intensity.
Sullivan
Okay. Moving on in this paper, we come to the spectra, which is the first time, I believe, that anyone put together some spectra of sources at frequencies between 40 and 160 megahertz.
Slee
Yes.
Sullivan
And can you tell me what you found and what you made of it?
Slee
Well, of course, we found that the only significant difference between the spectra, I think, was the Crab Nebula was flat and the others were much more steep, much steeper, I think, at the time we interpreted this, did we not, I’m not familiar with the paper now, in terms of the synchrotron -
Sullivan
No, no. This is before -
Slee
Before Shklovsky and company, was it?
Sullivan
Yes. This is before synchrotron days. I’ve forgotten exactly what your comment was on that.
Slee
We probably didn’t have any.
Sullivan
You say, “Taurus would be consistent with thermal radiation from an optically thin shell.” Which is correct, of course; it is consistent with that, but that’s all you say. And then you also have a spectrum of the North Galactic Pole and the region around the Galactic Center so that galactic background, throwing in some other observations by Hey and so forth, you showed had a steep spectrum also.
Slee
Yes, I’m not sure how closely it coincides with present day spectra.
Sullivan
No, I haven’t checked. Here you have over a factor of 4, in frequency it goes down by a factor of 25 in brightness temperature; so it should be 42.5, and 16-32, yeah that’s (?)
Slee
Towards the same (?)
Sullivan
Yes, it looks pretty good. Okay, and the final thing is indeed, the ionospheric fluctuations, and apparently you had observations from July 1947 through June 1949 that you reported in the paper.
Slee
That’s right. Cygnus, I think.
Sullivan
Right, this is all Cygnus-A. And you’ve already said you were quite convinced it was due to the ionosphere. There was one thing I wanted to check; you imply in the abstract that previously it had been felt -
End Tape 86A
Begin Tape 86B
Sullivan
Continuing with Bruce Slee on 1 March 1978. So apparently you were referring to the Hey, Parsons, and Phillips, 1946, where they suggested that it was intrinsic to the source.
Slee
Yes, I’m fairly certain that that would have been the case. I think that was about the only information we had at that time on -
Sullivan
There’s another interesting point here, though. You point out that Cygnus-A, and you had an upper limit for it at that time at 1½ arc minutes in size, twinkled because it was small just like the stars twinkle, and that some of the other sources which were extended were analogous to the planets. And I think that was the first time that people pointed out that that might be one reason for the variation in the scintillation indices, as we say now, of different sources.
Slee
Yes, that must have been, I think, a fairly novel idea at the time.
Sullivan
Were you working at all on this theory of the ionosphere, or was that once again mainly John Bolton?
Slee
I did most of the (?) analysis for the ionospheric work, which was published in a separate paper, rather later.
Sullivan
That’s right.
Slee
More statistical work and correlations and so on; most of it was done by me.
Sullivan
That was Bolton, Stanley, and Slee – Slee and Stanley – in 1953, “1947-1951 Low Altitude Scintillations for Four Radio Sources.” Well, just to finish this topic off, what did you find in that paper? What were the main results?
Slee
Well, we found that the scintillation behavior of the sources could be interpreted in terms of irregularities in the electron density in the ionosphere; mainly the main correlation we found was between sporadic E and scintillations, although there could have been some correlation with spread F for the peak which we obtained at midnight. We had two peaks in the apparent distribution; one at mid-day and one at midnight. These could be interpreted either as a seasonal effect because the source changed its time of rising through the year, twenty-four hours through the year, or in terms of a diurnal effect. We had no evidence either way.
Sullivan
I gather then that you, by this time, were becoming an ionospheric physicist essentially. You’re quite familiar with the literature.
Slee
Yes, I was fairly familiar with the literature at the time.
Sullivan
Let’s see what else. You find that the scintillation index was larger at the lower frequencies and at the lower altitudes as one might expect.
Slee
Yes.
Sullivan
This, now I’m not all that familiar with the ionospheric physics side of things. These were new results to the ionospheric physicists? Or were they mainly of interest to the radio astronomers trying to get rid of these effects?
Slee
I think they were essentially, as soon as we published the results, of course, the ionospheric physicists pointed out that some of their own results could be interpreted in terms of this small scale ionosphere scattering and fading which they got on space for some could be interpreted in terms of similar size blobs in the ionosphere, but it was not until we discovered this effect that such small scale blobs (?)
Sullivan
I see, I see. So that was mainly, perhaps the main result from an ionospheric point of view.
Slee
Yes.
Sullivan
Okay. Well, let’s take a break and we’ll resume later. [brief break] So in 1953, you and Bolton published what is fair to call, I think the definitive paper on the theory of the sea interferometer, and perhaps you could tell me what you see as the main advantages of the sea interferometer end the main disadvantages, relative to the Michelson interferometer which, of course, was being used at Cambridge at that time.
Slee
Well, one of the main advantages of the sea interferometer comes from the fact that you only need one aerial rather than two; you get the reflection in the sea as the additional element. It has another advantage in the fact that sources rise rapidly; coming, you might have a strong source below the horizon and a weak one preceding it. You got the weak one and then the strong one.
Sullivan
Right, there’s an occultation phenomenon.
Slee
Yes. So you’re able to detect weak sources in the presence of stronger sources, especially if they precede the stronger sources (?)
Sullivan
And if they’re rising anyway, as you were. If you could look both ways –
Slee
It’s a very cheap way of getting phase stability and reasonable resolution. You don’t need a high cliff and no long connection cables. You only need one receiver; you don’t need pre-amplifiers and so on. Its main disadvantage, of course, is the low frequency of the ionosphere and atmospheric effects, of course, can be severe, too. (?) in the atmosphere can rather wreck observations.
Sullivan
What about the fact that you can’t get a varied baseline. Did you find that much of a drawback?
Slee
Getting frequency, of course, you can’t vary the baseline, but if you assume structure remains the same, you can -
Sullivan
You’re making an assumption now.
Slee
That’s a very big assumption, yes. It’s rather difficult to vary the baseline on (?) around the country; different cliffs and that’s very inconvenient.
Sullivan
But you did do some of that, didn’t you?
Slee
Yes, that was done in the early days, trips to New Zealand and much of the Cygnus and Cygnus-A work and Crab Nebula, Virgo and Centaurus was done on trips to New Zealand.
Sullivan
For this mobile work, so to speak, were you using surplus radars that were designed for (?) or did you make up a trailer of -
Slee
We just made up a trailer of three or four (?) aerials which could be set on top and towed by truck – receivers inside and chart recorders – that was it.
Sullivan
And you just got your position from a map as to where each location was?
Slee
We used a surveyor’s map usually. (?) minute-of-arc kind of resolutions.
Sullivan
Let me ask about the technique from the beginning. What was its origin, really? Was it something that had been used as a radar technique in shipboard radars or - ?
Slee
What the sea interferometers?
Sullivan
Yes.
Slee
Well, it came from the Lloyd mirror experiment in optics really.
Sullivan
Right, but this is a long ways to go from that to an antenna on top of a cliff.
Slee
Of course, it was known from radar work during the War, that you got good reflection off the sea; and you form a lobe pattern and this is the basis of identifying the (?) aircraft flying into a radar beam waves of the (?) of the radar. And well, it was very obvious that it should work at source work, I think. Except that nobody up to that time had done it.
Sullivan
Right. So it was a direct, is it fair to say it was a direct outcome of military radar experience?
Slee
Yes. Of course, I used it on the sun at Dover Heights. That was the first experiment with the active sun by Pawsey and McCready.
Sullivan
Had these effects, refraction and so forth, been worked out for the military application also? Were there, sort of, standard tables, maybe not as accurate as you needed, but -
Slee
No, I don’t think. I think they had been worked out, but not as accurately as we needed the refraction corrections. The effect was, of course, anticipated.
Sullivan
What would you say, well, first of all, when were the last sea cliff measurements made? About what year?
Slee
Dover Heights, I think they were made about 1954 or 1955. I’d say -
Sullivan
That was -
Slee
1954?
Sullivan
That was producing this catalogue of 100 -
Slee
Yes. That was published in 1955, I think. Yes.
Sullivan
Can’t quite find it here now. Where are we? 1954, 104 Radio Sources.
Slee
Yes, well, it must have been early in 1954 that we stopped, I think, the sea interferometry. From then on, we were concerned with that 80-ft dish which - (break in the tape)
Sullivan
So at that point, the sea cliff interferometer was retired, so to speak, and I guess that you figured that flexibility just didn’t have enough to continue?
Slee
That’s true, yes.
Sullivan
To employ that technique, anyway.
Slee
At that time, the Mills Cross was in the offing at Fleurs, and had done the initial design and work on it; it would seem to be the instrument to take over the future survey work.
Sullivan
On the other hand, Bolton -
Slee
I think Reber at that time (?) island high resolution sea interferometry, I think he had a base of (?)
Sullivan
Oh, yes.
Slee
(?)
Sullivan
Oh yes, in Haleakala.
Slee
Yes, that’s right.
Sullivan
Reber - he never got much out of that. But he -
Slee
No, the atmospheric effects just ruined him.
Sullivan
But you’re right, he was another person who tried the sea interferometer. Just for my information, Bolton, however, of course, did not work in that group, so he wanted to continue radio source, or that’s when he went into rain physics, isn’t it?
Slee
That’s right.
Sullivan
Okay, that explains that. Anything else about the sea interferometer that I should know?
Slee
I don’t really think there’s anything important that we’ve missed about the sea interferometer.
Sullivan
You had to understand how the reflection coefficient changed with the sea state, of course, also, right?
Slee
Well, I don’t know that we knew too much about that. The effects of the waves on the -
Sullivan
Right.
Slee
(?) obvious on the record, but (?)
Sullivan
Was that something you just sort of lived with?
Slee
I think (?) the first few lobes this coefficient (?) That is what we normally used, the first dozen or so fringes as the source waves. We could reduce the source powers and so on from the ratio of the fringe (?) going to the (?) But otherwise, I don’t think we even considered the reflection coefficient in any quantitative way.
Sullivan
The change in height due to tides also had to be considered. Is that not correct?
Slee
Yes, that was considered in the (?) accurate source work in the New Zealand observations.
Sullivan
Did you just take standard tide tables or did you have actually something that measured the height?
Slee
No, I think they had to just take the standard tables and use those. They found them to be accurate enough.
Sullivan
So let’s talk about this survey that must have gone on for two or three years in which you ended up with 104 radio sources at 100 megahertz. Was this, indeed, covered a declination of +50° to -50°, so I guess you methodically covered this entire range.
Slee
Yes, that’s true. We used the aerial on the cliff, nine Yagi aerial, which was set up especially on the cliff edge for that. And we just turned the aerial around gradually from north to the south.
Sullivan
That seventeen-foot dish that I was showing you a slide of, that was used only at higher frequencies than 100 megahertz. What was the lowest frequency that had been used?
Slee
I think it was used, might have been used at 100, but certainly used up to 400 megahertz; I think mainly at the high frequencies, and we (?) the spectra, the height on the spectra, must have been obtained using that aerial.
Sullivan
What was your criteria for a source? How did something get into your catalog?
Slee
Well, it was obviously, the fringes had to be well above the noise level on the record, had to be repeatable at least twice, and the fringes had to last for a dozen or so fringes.
Sullivan
Were you concerned at all in terms of doing some calculations about what we now call confusion? To see whether this might be a problem?
Slee
No, I don’t think we were really concerned; we were only concerned with the number of sources per beam area and that’s remained very small. (?) unconcerned about (?) very strong sources out of the whole sky, so confusion was really a problem.
Sullivan
Right. And -
Slee
Of course, we didn’t know much about confusion problems anyway. In those days.
Sullivan
And can you remember about the distribution of these sources and what you made of that? Having a map now of these 104 sources?
Slee
I’m afraid I can’t remember anything specific about the distribution.
Sullivan
You had a remark here about a new concentration of faint sources in the southern galactic hemisphere. I’m afraid I haven’t checked the paper -
Slee
No, I don’t remember the circumstances of that remark at all. I really can’t answer that.
Sullivan
Okay, well, I can check that before I talk to John Bolton. Another question to ask is what sort of contact did you have, and awareness did you have of the work going on at Cambridge which was along similar lines in many respects?
Slee
Well, I think we didn’t have very much contact with Cambridge. I think we only read the papers they published and nobody had been over to England, I don’t think, in our group at that stage and seen what they were doing.
Sullivan
So you were operating pretty much independently, except for published papers.
Slee
That’s right.
Sullivan
Do you happen to remember how this survey agreed with the 1C survey of Ryle, Smith, and Elsmore?
Slee
No, I don’t remember that at all really. I would suspect that they didn’t agree too well at all. I remember the 1C survey was completely confusion-limited in many respects. I had, well, I suppose the strongest sources are the (?) had many more sources than we possibly detected on our system.
Sullivan
Well how it now, the 1C is 1950 with about 50 sources. The 2C is the one with the 2,000.
Slee
That’s right. That’s the one we (?) Mills Cross.
Sullivan
Right, which came out in 1955. So this was after your survey here. Okay. Well, let’s move on. What was the next thing you worked on once the sea cliff interferometer work was ended?
Slee
I think towards the end of the sea interferometer work the 80-ft dish was, which we dug in the ground in our lunch hours and so on, was coming into operation.
Sullivan
The hole-in-the-ground?
Slee
Yes.
Sullivan
What do you mean you dug it in your lunch hours?
Slee
Well, John Bolton and Gordon and I used to get out with wheelbarrows and dig out the sand during our lunch hours.
Sullivan
And then what were you doing during your normal day?
Slee
Just working with (?) equipment. Surveying, analysis. But we used to do a lot of things during our lunch hours. We used to plot (?) and keep the (?) hold the sand we used to put grass in and dig the trenches.
Sullivan
It sounds like it was more like an outdoor work hour than a lunch hour.
Slee
Yes. We did everything out there.
Sullivan
But at first it was not covered in concrete; it was just a hole, is that right?
Slee
It was just a hole initially, the original one, and then there was another one after that that was concrete.
Sullivan
And do you remember what the, where the idea for this dish came from? Was the one existing at Jodrell Bank at that time?
Slee
I think it was, yes, I think -
Sullivan
I think it was, yeah.
Slee
Yes, that was where the idea must have originated. This had a long focal length to swing the beam twenty or thirty degrees without too much distortion to the beam. I think it was then that we, I think Gordon Stanley started it off by using it for a search for the deuterium line (?) megahertz with negative results.
Sullivan
That’s right. Dick McGee has told me about that also.
Slee
And then we did a survey, I think at this stage, John had more or less left for the cloud physics section, and Dick and I, and I think perhaps Gordon was uninvolved in the early stages, did a survey on the Milky Way with the dish at 400 megahertz.
Sullivan
That’s right. That was 1955 that you published that. And what were the main results of that survey?
Slee
Oh, we discovered, I think the main result was that we discovered the Sagittarius A source in the Galactic Center. Plus, several other non-thermal concentrations along the plane. I think the main result was Sagittarius A.
Sullivan
You say, “non-thermal,” did you have spectra for some of these discreet sources?
Slee
Well, no. It just turned out subsequently that they were(?) sources. At the time we didn’t have the spectrum.
Sullivan
And the Sagittarius A result is, of course, quite interesting. Were you quite convinced that this was something to do with the Galactic Center or what did you make of this?
Slee
Well, we weren’t convinced, but I think we were fairly certain that this was essentially in the Galactic Center source. I think at the time the Andromeda Nebula (?) surveyed at Jodrell Bank, and a nucleus had been found in that source.
Sullivan
I’m not sure about that, no. I think it was just distributed, you know, definitely an extended source that more or less agreed with the optical image, but I don’t think there was any nuclear concentration. I may be wrong on that. But this brings up another related question – during this time, you must have gained quite a self-education, so to speak, in astronomy learning about our Galaxy. Was this just from reading journal articles or how did you go about doing this?
Slee
Mainly through just reading. We had no formal courses in astronomy. I didn’t get any anyway; I don’t think John did either.
Sullivan
There were no informal lectures within the Radiophysics where one person was studying one thing and talked about it to the others, or anything like this?
Slee
Not that I can remember, no. I think everybody did their own thing and just wrote it up and did the best they could.
Sullivan
Were there ever any literature journal club-type things in the Radiophysics Lab? For the review of current literature?
Slee
No. We had colloquia from time to time, that people presented on their own results, but I don’t think there was any organized attempt to review the literature and give a seminar. I rarely went into the laboratory in those days. I must have been at the laboratory only once or twice a year, actually.
Sullivan
Oh really, that infrequently?
Slee
Yes, I lived out at (?) close by and went straight out to the (?) perhaps a school in (?) on the way home, John and I, in the summer.
Sullivan
I guess that was true for a lot of people that spent very little time at the lab itself.
Slee
Yes, that’s right. That’s true.
Sullivan
Which once again, once again led to these small groups as really important unit as opposed to -
Slee
(?) important in keeping these groups together as an entity.
Sullivan
How did Pawsey control the -
Slee
Oh, just by going around very frequently and keeping his finger on the pulse, I think. I think he was the real cohesive force at that time.
Sullivan
In what sense do you mean that? He was head of the Radio Astronomy (?)
Slee
Yes. Well he kept and overall view of research going and suggested new line, I think, for research.
Sullivan
And was he free to and often assigning people from one group to another or was it mainly just in strong suggestions that these changes took place?
Slee
He was very forceful in changing people around. He tended to keep them together. But, no, there was very little (?) you know five or six years, 1947-53 say, there was very little interchange between groups.
Sullivan
And did that change somewhat after 1953? Was there more?
Slee
Yes, there was with Cygnus, Mills’ Cross going on and Potts Hill, the hydrogen line work out at Potts Hill – there was quite a bit of changing went on then. For instance, I left Dover Heights about 1955 or so and went to Fleurs to work with Bernie Mills on the Mills Cross. And Kevin Sheridan came to the group, too, about that time, the Mills Cross group.
Sullivan
Okay. Another question that comes to mind is John Bolton, up to this time, of course, had a number of successes, to say the least, in radio astronomy – why did he switch to rain physics?
Slee
Well, because the chief of the division was a very good cloud physicist and I think he made it attractive to John to leave radio astronomy and go into cloud physics (?) group sort of stirred up a bit (?) and he offered John some good inducements to go over and spend at least two or three years with the cloud physics group, which he did. And then he (?) after he left for the United States, California.
Sullivan
Right. Okay. What else was there with this 80-ft hole-in-the-ground, was this what you did the occultation of Taurus A with?
Slee
No, I didn’t.
Sullivan
What did you use for that?
Slee
Fleurs.
Sullivan
I’m sorry, yes. East-west arm of the Mill’s Cross, I have it right here.
Slee
(?) occultation of (?)
Sullivan
And what were the main results, you did this several years, I think.
Slee
Yes, well, we just deduced the variation of the scattered radiation as a function of separation from this angular separation from the sun for several years, and then interpreted that in terms of radio electron densities in the corona of the sun. That was the main object of that work.
Sullivan
And I suppose you were aware of the similar efforts that were going on at Cambridge and I think elsewhere also at that time.
Slee
I think mainly at Cambridge and Russia in the Soviet Union started about the same time, Vitkevich of Russia.
Sullivan
Right. He was the first one to suggest it perhaps.
Slee
Well, he claims he was, I think. I don’t know if he did or not. I think the Cambridge people started a couple of months before (?) did on that. In fact, it was, I think, I wasn’t too sure some of those results were sound check it with the east coast arm of the Mill’s Cross.
Sullivan
That would give you a fan beam. I noticed that the abstract says here that you had a pencil beam, and how was that achieved, also?
Slee
Well, the Mill’s Cross itself is a pencil beam.
Sullivan
You had an entire Mill’s Cross?
Slee
Yes.
Sullivan
And you had an interferometer, what was that?
Slee
That was a couple of (?) aerials out in (Perth?) which we could combine with the north-south arm of the cross as a switched Dicke System.
Sullivan
And what would be the advantage of, for instance, having this fan beam instead of the pencil beam?
Slee
Well, the fan beam is narrower than the pencil beam. As soon as you combine two aerials together in the Mill’s Cross system, the power response is proportional to the voltage response of each aerial.
Sullivan
Oh, that’s right.
Slee
You use an aerial fan beam in total power mode to get appreciably better resolution.
Sullivan
I must admit that point’s never hit me before, that you get better, yes, I see now. Okay. Now, there’s another little article here about Hydra A being monitored for 12 months.
Slee
That was work out at Dover Heights, actually, before I left the sea interferometer.
Sullivan
Working with which dish?
Slee
With the interferometer on the cliff, the 100 megahertz (?)
Sullivan
And did you use other antennas, also for the monitoring?
Slee
No, only used the one monitor for a year or so. (?) and continued that work out at Fleurs using the Mill’s Cross, using the east-west arm.
Sullivan
Was this purposeful monitoring program and was there any theoretical impetus – any reason why you were looking for it, or just why not?
Slee
Well, I started the, actually, the Mill’s Cross east-west observations, started in order to look for transient radio sources. Of course, I saw, in the east-west arm, you see the whole twenty-four hours of each day coming through the fan beam, keep a check on the daily intensities, and again Hydra seemed to be variable. That’s when I published that paper, as a result of those observations.
Sullivan
That’s what you say, more variable than that of other sources, so you were checking them relative to each other.
Slee
Again, at Dover Heights, with Taurus and Virgo and the other sources as control.
Sullivan
And this is at, what, 80 megahertz or so?
Slee
This is 80 at Mill’s Cross and 100 megahertz at Dover Heights.
Sullivan
Now, I think it turns out that Hydra is not that variable, is that correct?
Slee
Well, -
Sullivan
Or maybe it was then.
Slee
Apparently not.
Sullivan
What do you think was happening?
Slee
I suppose it was possibly ionospheric. It just happens that (?) years you view along the magnetic field lines, and I think that this maybe -
Sullivan
The Earth’s magnetic field.
Slee
Yes, and you (?) maybe (?) focusing fix and (?) reflection possibly must have given us a confusing picture at the low frequencies.
Sullivan
Is it somewhat smaller in the angular extent, so it might be more subject to -
Slee
Yes, it’s only a minute of arc at the most. It’s rather smaller than the other strong sources around it in the sky.
Sullivan
But nevertheless, that’s quite interesting because, of course, source variability in the sixties turned out to be a very important subfield.
Slee
It just happens to be the wrong wavelengths to detect it, that’s all.
Sullivan
Well, even yet later in the seventies, now we do have low frequencies, but not with the sort of sensitivity that you had then.
Slee
I use these records again to (?) sources that, correlations with geomagnetic activity and so on. This is the data from the east-west arm of the Mill’s Cross.
Sullivan
I see, and did you publish that in the late fifties?
Slee
Yes, it was published somewhere. It should be -
Sullivan
I don’t think I have that reference.
Slee
It was published -
Sullivan
It may not have made the radio astronomy bibliography if it was on the ionosphere.
Slee
No, it was ionospheric work. [pages turning]
Sullivan
Australian Journal of Physics, 1952, okay.
Slee
I was also one of the first people who looked at satellite scintillation.
Sullivan
Yes, I was just noticing that paper. First of all, which satellite was 1958 alpha?
Slee
That was the first American satellite.
Sullivan
So that was Vanguard? No, no. What was that? Not Explorer? I think it was Vanguard. Well, anyway, it was small.
Slee
Yes, very small.
Sullivan
And you looked at its scintillations and found also approximately seven second modulation according to the abstract, what was that?
Slee
That must have been the Faraday rotation (?) got in there that I interpreted (?) set the time.
Sullivan
Why did you get this periodicity?
Slee
Because of the rotation of the satellite; it was a polarized radio aerial and it was rectangular, it was probably (?) satellite rotation (?) Faraday rotation (?) aerials (?) polarizing the ground.
Sullivan
I see.
Slee
(?) which effect it is now, I’ve forgotten the details.
Sullivan
Were you using just a rigid up interferometer for looking at this satellite?
Slee
Yes, I had a special tin dipole, I think, interferometer on the ground.
Sullivan
Let’s see now, I just noticed that you and Bolton gave this Hydra A variation paper at the Jodrell Bank 1955 Symposium. Did you yourself go to that?
Slee
No, John was there.
Sullivan
Just out of interest, when was the first time you went to a meeting outside of Australia?
Slee
Not until I went to England in 1964.
Sullivan
Oh, I see.
Slee
Had the URSI here in 1950.
Sullivan
1952. Did you go to that?
Slee
Yes.
Sullivan
Do you have any recollections of the radio astronomy activities in that?
Slee
Well, of course, I put some time on a meeting on the people from overseas at Cambridge and so on. Nothing particularly strikes me. Of course, at that time, there was a lot of talk about the angular search which was going on in the initial measurements at Cambridge and Bernie Mills was making (?) sources. I think that was one of the highlights of the meeting.
Sullivan
And the Cygnus A identification (?)
Slee
Nothing strikes me as being particularly important.
Sullivan
Was there during this period, relative to Cambridge, always sort of a sense of competition?
Slee
There was subdued a sense of competition, I think, I don’t think it was very rampant, not as far as I remember.
Sullivan
Well, I’m just asking from your point of view.
Slee
Other people have claimed there is.
Sullivan
Okay. You had a paper with Westfold, Bolton, and Stanley in 1954 in which you talked about large radio sources, greater than degree in size.
Slee
Yes.
Sullivan
One of these being, of course, Centaurus A. What in the world did you make of such a large source connected with a few arc minute size galaxy? Were you really sure that -
Slee
I don’t think we came to any conclusions in the paper about that, did we? The possible mechanisms of radio emissions?
Sullivan
No, I’m trying to get a feel for what you thought of it though. Were you thinking that it was an explosion or something out of which the galaxy condensed, or did you have any ideas along those lines?
Slee
Well, I think the explosion idea is probably the main ejection of gas and (?) from the galaxy is probably the main feeling we had.
Sullivan
Of course this was colliding galaxy days and so this explosion would have been triggered by the collision of the galaxies.
Slee
That would be the main feeling, I think, that I would have had at that time.
Sullivan
All right. The next thing is the Mills and Slee paper in 1957. The first installment of the large survey, and perhaps if you could tell me about how you got involved with Bernie Mills and his cross and the survey and what the goals of the whole project were.
Slee
Well, I’d been responsible for taking much of the data to ensure the operation of the Cross and getting the with us, and we decided to, or Bernie decided it would be a good idea to do a preliminary assessment of the records and get some feel before we started the main analysis. We used records we had taken during the testing phase of the Cross. We (?) switching, beam switching system working, we just had a single beam kind of data to look at. We went quickly through the records and measured the intensities -
Sullivan
You had the 2C survey.
Slee
Yes. Of course, we measured the intensities and positions of the sources we could see on these records, did the statistics of the log-n/log-s curves.
Sullivan
Once again, let me ask you, what did you define as a source?
Slee
Well, an obvious bump on the record which appeared to fit the size of the beam, carried on at least two successive (?) runs of the declination runs in the sky. We would shift the beam slightly each night. (?) We would know the (?) so that it would have to be discrete and stand out above the noise level.
Sullivan
It could be larger than the beam, could it not, if it were extended?
Slee
Well, on the same order. I mean (?) of course, but we certainly weren’t restricted to point sources. It had to be an obvious bump which was consistent with having passed through the aerial beam, and three times the aerial beam would be about the maximum kind of source size that you consider.
Sullivan
And if it were larger than that, you would take it as a - receiver?
Slee
Irregularity. Bernie talks a little bit about background (?) galaxy, galactic structure -
Sullivan
As opposed to discreet sources? I see. So those would not be catalogued?
Slee
No, if they were we’d just made a note usually.
Sullivan
Now here you were more concerned about confusion problems, I think, is that fair to say? Did you work at all on that sort of analysis or was that mainly Bernie Mills that - ?
Slee
Oh, it was mainly Bernie Mills’ work on that confusion analysis and what we expected confusion (?) I was concerned mainly with getting the results at that stage and doing the record, actual record analysis. I didn’t do much interpretive work then.
Sullivan
I see. So is it fair to say that the tone of the paper which is very much, not so much to present your results as to say that Cambridge ones are all wrong, was mainly Bernie’s?
Slee
I think so, yes.
Sullivan
Although did you concur in all this? Or would you have done it differently?
Slee
No, I think I concurred all right; I went through the analysis and checked it after Bernie produced his figures, and I think I agreed that (?) hardly would determine the paper.
Sullivan
Was there any, here it is, what do I want to say? What was your feeling about the work from the Cambridge group? Did you feel that they did not understand how to analyze this data or that they were, I mean, how did you feel that they had gone wrong? And why?
Slee
Well, we thought that the interpretation of interferometer records was far too enthusiastic. I mean, we thought they ignored the problems inherent in many sources, (?) and haven’t worked out correctly their confusion (?) That was my conclusion, I think.
Sullivan
Right. Which the Mills Cross technique was not so subject to.
Slee
Susceptible to such, we had our own problems with side lobes, of course, but we considered them adequately. Strong sources in the side lobes, we thought we knew where all the side lobes were appearing and to ignore those sources.
Sullivan
It would be interesting for me to know how much analysis did it take, say for one day’s strip chart records, did it take an hour to go through it? What was the ratio of time?
Slee
Gosh, Eric Hill and I did the main analysis of the records. (?) typical record (?) beam switching technique going. This is a source coming through here, and we used to switch between four (?) positions on the (?) and then come back to the original. And you had to do tracing (?) trace all these, each beam separately first, and then disperse the tracings vertically. And these little tracings that we worked.
Sullivan
So you had a girl or two assisting you in this?
Slee
Yes, we had one girl doing tracings. Eric and I would come along and look at the tracings and measure up the source positions and intensities, decide which were real sources and which were side lobes.
Sullivan
Was much of this done unattended?
Slee
Yes, most of this was done unattended. Not binocular recording was done totally unattended. We had to (?) -
Sullivan
And would this be an example of -
Slee
An extended source, I think.
Sullivan
Would this get catalogued? This extended thing here?
Slee
I think it probably would be, yes. Side lobe of Centaurus A this is (?) 13-30. I think that would have been a genuine extended source. There’s a side lobe there.
Sullivan
Gone negative, yes.
Slee
That’s probably Centaurus A; see this is 13 hours, 13:20. That would be Centaurus A.
Sullivan
How far away did these side lobes from a strong source like Centaurus bother you?
Slee
Oh well, you could, almost thirty-forty degrees of that. Of course, you have your east-west had a very wide beam north-south. Something like forty degrees.
Sullivan
Right.
Slee
So whenever a strong source transited, you would expect that. Either positive or negative side lobes.
Sullivan
You said that Bernie Mills did most of the analysis. Nevertheless let me ask you about whether you have any comment on one statement in here in the conclusions, it says: “An analysis of our results shows that there is no clear evidence for any effect of cosmological -
End Tape 86B
Begin Tape 87A
Sullivan
This is continuing with Bruce Slee on 1 March 1978. As I was saying, note: “for any effect of cosmological importance in the source counts.” Now, when I read that to Bernie Mills and I said to him, “But you did get a definite log-n/log-s which was much more consistent with a steady state universe, and so how can you say there’s no cosmological importance to the counts that you have?” And do you have any comment on that point? Or were you really not wondering about the cosmological aspects of the survey?
Slee
Well, I think Bernie was interpreting the cosmological implications in terms of the Big Bang Theory, wasn’t he?
Sullivan
Right.
Slee
And he was expecting, so I think he was really saying that there were, there’s no evidence for any definite kind of evolution of the universe.
Sullivan
Well, I agree with you, but that’s a very important cosmological -
Slee
I agree.
Sullivan
Now, what he said -
Slee
Probably at the time, I didn’t recognize it, but I do now.
Sullivan
What he said a couple of years ago was that it was not clear to him that these sources were far enough away that they could tell you about anything cosmological to begin with. Of course, in any kind of universe, the nearby sources give you a 1.5 sort of slope, and so he wasn’t clear that this could tell you about one universe from another. But I don’t know, it seems a little ambiguous to me. He did come up with a much higher space density of sources, making various assumptions, than Ryle and Scheuer did, about a thousand times. Which, of course, would then mean that the sources were much closer on the whole.
Slee
No, I’m inclined to think that it was a result of some cosmological significance.
Sullivan
Was it played up in the Australian press in a similar fashion to how the 2C results were played up in the British press? And maybe down here also. The results of this survey? In terms of -
Slee
Well, there were quite a few newspaper articles about it, but I don’t think it was extensively covered.
Sullivan
But was the tone of what you were telling the reporters that steady state might be right after all, in spite of the results of the Cambridge survey?
Slee
What about the tone?
Sullivan
Was that the tone of what you were saying?
Slee
Yes.
Sullivan
That it could not be definitely excluded as the Cambridge people said.
Slee
Yes, that’s true.
Sullivan
I’m going into this, of course, because it is one of the more interesting controversies in the development of radio astronomy. You get a statement like at Princeton, the abstract – “It is found that the two surveys are almost completely discordant.”
Slee
[laughter] Couldn’t get a more definite statement than that.
Sullivan
No, indeed. It’s refreshing to see a statement like that. Usually people waffle much more in scientific papers. Well, that was just the first part of the survey, as you said, and then, I guess it took two or three or four more years to do the entire survey.
Slee
Yes.
Sullivan
Were there any changes that you made while you were making this survey, in procedures as you learned, or was it pretty much all -
Slee
No, I think there wasn’t any basic change in the way we did the surveys. We had this beam switching technique which produced (?), but (?) much more quickly.
Sullivan
And you just kept grinding away putting out the sources?
Slee
Yes. It was about three years, I think, before we had written all three catalogues.
Sullivan
Right. There was one in 1958, one in 1960 and I think there was still one after 1960. Now in the 1960 paper, the abstract says, once again, that you have a log-n/log-s with a slope of 1.5 which “is the expected slope for a uniform distribution in a static Euclidian universe.” Now that doesn’t say that you believe that there is a static Euclidian universe, but once, again, that would seem to me to be implying that you were saying that the radio sources are telling you about the structure of the universe.
Slee
Yes, I agree.
Sullivan
And I’d be interested, have you read Edge and Mulkay’s version of this controversy in their book?
Slee
No, I haven’t read it.
Sullivan
Well, they have various opinions on what caused the differences here and then how they were finally resolved. They basically concluded both sides made errors in their surveys. The Cambridge errors being somewhat more grievous, shall we say? But how do you view the whole thing in terms of the two different approaches? Was it a different philosophical approach or was it simply a matter that the two groups happened to end up with two different techniques and it could have been the other way around?
Slee
Well, I think it was a different philosophic approach. I don’t think we would have drawn the conclusions that they did from the data; we would have been must more cautious, I think, about planning with the log-n/log-s curve, sloped up readily, low fluxing and -
Sullivan
Perhaps wouldn’t have listed anywhere near so many sources to being with?
Slee
Sure. I think we would have been very suspicious of the weak end of the distribution.
Sullivan
Did you have any special techniques to take care of the weak end of your distribution? In terms of making sure your lower cut-off of (?) sources were very high?
Slee
No, we didn’t have any special techniques. Well, I think you can see on our plots that we plot the log-n/s points that at the low end of the frequency (?) I think we realized at that point that we reached the limit fairly high flux level, and the results were not meaningful below that flux unit. I think the Cambridge people continued theirs down to a much lower flux level, 4 or 5 flux units.
Sullivan
Yes, I think in retrospect, in my analysis of it, that you underestimated your confusion limit a little bit, also. So you think that’s a fair statement?
Slee
Yes, Bernie did.
Sullivan
Not as badly as Cambridge, but nonetheless, somewhat. It didn’t affect the overall conclusions significantly. Was this during this period of the survey, was this a thing of constant conversation and analysis and so forth? As to what did all this data meant? Or were you mainly concerned with working with these strip charts and getting -
Slee
No, mainly of getting the results first, I think. We didn’t speculate too much about that, there were one or two special projects which, looking at HII regions and things like that, which were done as we were getting the results out.
Sullivan
Just as a sideline? As a matter of fact, here’s a survey of the ten-degree Milky Way strip, Hill, Slee and Mills, 1958. Is that what you were referring to in the HII regions?
Slee
That’s one of them. Other people involved, Kevin Sheridan and Alex Little, and so on. Special (?) HII regions and the Orion Nebula and so on.
Sullivan
You also took time out to look, with Shain, at Comet Arend-Rdaud
Slee
Yes, negative result.
Sullivan
Right. Which, however, was fifty times less than Kraus’ detection, which indeed, that seems to be spurious now. There are other people who did not confirm his results. Was that using the Shain’s Mills Cross?
Slee
And (?), wasn’t it?
Sullivan
Oh, I see, yes both of them – 20 and 85 megahertz, right. They were right parallel of each other, is that correct?
Slee
Yes, that’s correct. One just outside the other.
Sullivan
There were no particular problems with them interfering with each other?
Slee
Not really. His was a very open thing, very effective in far different wavelengths, quite an open type construction.
Sullivan
Well, when this Mills Cross survey was completed, then what was the next step for yourself?
Slee
Well, I’d become interested in the continued, Shain had started some Jupiter work, at Fleurs 19.7 megahertz, which he kept doing in between his survey work, galactic survey. And I became interested then in Jupiter work, to some extent, and I just, just a moment, before we get onto that, towards the last two or three years of the survey, we began building up an interferometer, a spaced interferometer, using one arm of the Mills Cross, the north-south arm, and an east-west arm space developed 20 kilometers away. This was never published as a separate thing, but you’ll notice in the last couple of catalogues, we refer to the angular size of some of our sources. In footnotes, and so on; this came from that. We brought out our short east-west arm, 20 kilometers away, had a radio link which -
Sullivan
I see; I wasn’t aware of that.
Slee
(?) and we combined the data with the North Star then. So we went over the whole sky with this interferometer, just looking at the stronger sources with the other arm wasn’t as large as the (?), so the effective area wasn’t as good, but we (?) a place, (?) on many of the sources, which were put in as foot notes in the last two catalogues. So that occupied us for another year or so, that little project by itself. I was involved in that to some extent. And about the same time, I started looking at Jupiter on a long baseline, using this same radio link, which we were using on this cosmic thing, using that on Jupiter. We had the (?) Cross (?) aerials, space (?) and radio link back to Fleurs.
Sullivan
Was this in conjunction with Alex Shain, now?
Slee
No, he’d died at that stage. And Charlie Higgins (?)
Sullivan
Was he the one that got you interested in Jupiter, would you say? Or how did you, it seems rather different from (?)
Slee
Yes. I don’t know quite how I became interested. (?) was doing a bit of work on Jupiter at high frequencies at Fleurs, started at Parkes in about 1962, I believe.
Sullivan
So what results came out of that?
Slee
We were able to place the first upper limits on angular size of the Jupiter source that showed that it was really much smaller than a disk object, and that at a few seconds of arc of radio size. And I carried on that work, trying to refine it the next two years, 1960-63, using various baselines to actually try to measure the size of the source. We set up a station on the south coast, about 150 kilometers south of Sydney. We had various (?), used Fleurs and we used at New Castle, on the mountain, to get the line of sight for the radio link. We set our aerial at each of those we waited for Jupiter storms and measured the (?) amplitudes. I found that the source seemed to be resolved at the longer spacings and this (?) interstellar (?) In fact, we were only measuring Jupiter source last (?)
Sullivan
Did you realize that at the time?
Slee
No. Only when the scintillation work on QSOs began to realize that (?) that we were dealing with a scattering medium between us and Jupiter.
Sullivan
Let me go back to the radio source size work. Were you at all surprised by, presumably you were finding many very small sources, was this at all surprising?
Slee
Well, I don’t think I was very surprised.
Sullivan
What sort of upper limits – what was the smallest - ?
Slee
Those, I mean, we were talking about ten arc seconds, I suppose, that was about our best resolution we could get on the interferometer.
Sullivan
Well, that’s about as good as anyone was doing at that time, was it not? A paper comes to mind, by Palmer, Thompson and Morris in 1957, in which Jodrell got some (?) ten arc seconds limits for what we now know as a couple of quasars and so forth. Were you at all influenced by that paper? To see how many of these sources?
Slee
Well, I think we were, yes. They must have started the work on building the interferometer about that time, the first interferometer. (?) I forgot to mention, we had that initial interferometer which was initiated by Bernie Mills and the group, and then Peter Scheuer came out for a couple of years and we extended the work. He had several spacings east-west and north-south, I worked with Peter Scheuer on it for a couple of years. That was about the same; I was doing the Jupiter work about the same time.
Sullivan
This was 1960?
Slee
1959 to ’62 – about that time. That work was never published either for some reason, Peter Scheuer took all the records back to England with him and -
Sullivan
Never said a word.
Slee
But some of that work is still really useful. Never going to see all that now, to that resolution in the southern sky.
Sullivan
With different position angles.
Slee
Well, we had east-west and north-south, but we could get down to two or three seconds of arc.
Sullivan
I hadn’t realized it hadn’t been published.
Slee
(?)
Sullivan
I have talked to Scheuer and he told me about that; I didn’t realize it wasn’t published.
Slee
What did he say about it?
Sullivan
Well I’m afraid I can’t remember. I do remember when he came down here.
Slee
Well, I started the Jupiter work, I was using the same radio link and the same aerials, I was doing some (?) scattering work with the same equipment.
Sullivan
This visit of Scheuer is interesting from another point of view, namely that there was some animosity between the Cambridge and Sydney groups. Certainly rivalry, and yet, here you had someone coming into the enemy camp, so to speak.
Slee
Yes, it was funny.
Sullivan
How was that arranged?
Slee
I don’t know how it came about. I can’t remember the details.
Sullivan
Was there a bit of a truce move, do you think? A peace offering?
Slee
It could have been.
Sullivan
But no one has ever worked at Cambridge for a year or two from Radiophysics, is that correct?
Slee
No, I can’t think of anyone.
Sullivan
I can’t think of anyone myself. Very interesting. Well, thank you very much. It’s been very interesting. This finishes talking with Bruce Slee on 1st March 1978
End Tape 87A