[Cover of Sullivan's book 2009, Cosmic Noise]
Sullivan's Cosmic Noise, Cambridge University Press, 2009


NATIONAL RADIO ASTRONOMY OBSERVATORY ARCHIVES

Papers of Woodruff T. Sullivan III: Tapes Series

Interview with O. Bruce Slee
At CSIRO Radiophysics
1 March 1978
Interview time: 85 minutes
Originally transcribed by Pamela M. Jernegan (1979), retyped to digitize by Candice Waller (2016)

Note: 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.

Click start to listen to the audio for tape 86A of the 1978 interview.

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 Ė 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 Iíd seen some report that Radiophysics was interested in this kind of research. So I immediately sat down and wrote a report on what Iíd 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

Thatís 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 donít remember of any report circulating through from the New Zealand or Australian military at that time of solar interference?

Slee

No, the only report Iíd 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 hadnít seen Heyís report?

Slee

No. I hadnít 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 Georgeís 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 Georgeís 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 didnít 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

Thatís interesting. This is 1947?

Slee

Yes, the end of 1947, early 1948.

Sullivan

And of course, you didnít publish this until 1950 Ė this paper weíve 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 Ė one of the rare cooperations between Jodrell and Cambridge in which they did the same thing that youíre talking about, with a smaller baseline. And thatís usually given the credit for having established this, but youíre saying that three years before you -

Slee

Well, two years anyway.

Sullivan

You were pretty convinced that it was that way, but you didnít publish it right away.

Slee

We were quite sure at the time, yes.

Sullivan

Do you remember particularly why?

Slee

I donít know. I guess we didnít 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 didnít seem, Iíll 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. Iím just puzzled why you didnít just send a letter off to Nature about the main results.

Slee

It is rather strange. We would these days Iím 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 heíd 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 youíre 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. Iíd 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 8í to 10í 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 Ė no doubt about that. The, were you in contact with, Iíve heard Harley Wood was leading you on to some of this optical information. Were you involved in any of that yourself?

Slee

No, Iím 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 didnít really do much of that. John did most of that.

Sullivan

Okay. Iíll check with him. Because, as you know, there were some that didnít 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, letís 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 itís (?) sensitivity. For some reason you werenít willing to use it at that stage. Was that (?)

Slee

We had a pretty crude mechanical switch from the Dicke system; we didnít have the electronic switching at that stage.

Sullivan

You didnít actually use it, I donít think. But you consider it here in this paper, thatís what Iím 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, thatís 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 couldnít use cold waves, so you had to have a hot wave (?)

Sullivan

Okay.

Slee

Bounce it against (?) keeping the hot lead stable.

Sullivan

Thatís true. And of course, thereís less motivation to use a Dicke switch because of the signals are stronger basically Ė youíre not as subject to gain fluctuations. Itís not as critical a problem. Would you agree with that?

Slee

Youíre limited more by the receiver, the noise background (?) receiver noise temperature, of course. Thereís not that great an incentive to use the Dicke switch, really.

Sullivan

Letís 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 wouldnít 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 weíd 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, thatís right.

Sullivan

Thereís another interesting column in this table; thatís 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 weíd 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, itís more like ten or twenty typically. Still thatís 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 Iím 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 Ė for several years there, we often had blackouts.

Sullivan

You didnít have your own generator?

Slee

No.

Sullivan

Once again, was that just a financial problem?

Slee

I donít know why we didnít go in for a generator. We could have quite easily; there wasnít 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 hereís another part of the paper where you talk about temporary sources, which may be a temporary source, interesting terminology Ė 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 Ė

Slee

Yes, they were. Of course, youíre subject to typical interference patterns Ė 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 didnít 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, Iím 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. Iíve forgotten exactly what your comment was on that.

Slee

We probably didnít have any.

Sullivan

You say, ďTaurus would be consistent with thermal radiation from an optically thin shell.Ē Which is correct, of course; it is consistent with that, but thatís 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, Iím not sure how closely it coincides with present day spectra.

Sullivan

No, I havenít 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 thatís (?)

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

Thatís right. Cygnus, I think.

Sullivan

Right, this is all Cygnus-A. And youíve 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

Click start to listen to the audio for tape 86B of the 1978 interview.

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, Iím fairly certain that that would have been the case. I think that was about the only information we had at that time on -

Sullivan

Thereís 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

Thatís right.

Slee

More statistical work and correlations and so on; most of it was done by me.

Sullivan

That was Bolton, Stanley, and Slee Ė Slee and Stanley Ė in 1953, ď1947-1951 Low Altitude Scintillations for Four Radio Sources.Ē 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. Youíre quite familiar with the literature.

Slee

Yes, I was fairly familiar with the literature at the time.

Sullivan

Letís 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 Iím 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, letís take a break and weíll 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, thereís an occultation phenomenon.

Slee

Yes. So youíre able to detect weak sources in the presence of stronger sources, especially if they precede the stronger sources (?)

Sullivan

And if theyíre rising anyway, as you were. If you could look both ways Ė

Slee

Itís a very cheap way of getting phase stability and reasonable resolution. You donít need a high cliff and no long connection cables. You only need one receiver; you donít 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 canít get a varied baseline. Did you find that much of a drawback?

Slee

Getting frequency, of course, you canít vary the baseline, but if you assume structure remains the same, you can -

Sullivan

Youíre making an assumption now.

Slee

Thatís a very big assumption, yes. Itís rather difficult to vary the baseline on (?) around the country; different cliffs and thatís very inconvenient.

Sullivan

But you did do some of that, didnít 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 Ė receivers inside and chart recorders Ė that was it.

Sullivan

And you just got your position from a map as to where each location was?

Slee

We used a surveyorís 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 donít 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. Iíd 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

Canít 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 didnít have enough to continue?

Slee

Thatís 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, thatís right.

Sullivan

Reber - he never got much out of that. But he -

Slee

No, the atmospheric effects just ruined him.

Sullivan

But youíre 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 thatís when he went into rain physics, isnít it?

Slee

Thatís right.

Sullivan

Okay, that explains that. Anything else about the sea interferometer that I should know?

Slee

I donít really think thereís anything important that weíve 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 donít 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 donít 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 letís 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 +50į to -50į, so I guess you methodically covered this entire range.

Slee

Yes, thatís 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 donít think we were really concerned; we were only concerned with the number of sources per beam area and thatís 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 didnít 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

Iím afraid I canít remember anything specific about the distribution.

Sullivan

You had a remark here about a new concentration of faint sources in the southern galactic hemisphere. Iím afraid I havenít checked the paper -

Slee

No, I donít remember the circumstances of that remark at all. I really canít 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 didnít have very much contact with Cambridge. I think we only read the papers they published and nobody had been over to England, I donít 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

Thatís right.

Sullivan

Do you happen to remember how this survey agreed with the 1C survey of Ryle, Smith, and Elsmore?

Slee

No, I donít remember that at all really. I would suspect that they didnít 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

Thatís right. Thatís the one we (?) Mills Cross.

Sullivan

Right, which came out in 1955. So this was after your survey here. Okay. Well, letís 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

Thatís 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

Thatís 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, ďnon-thermal,Ē 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 didnít 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 werenít 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

Iím 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 donít think there was any nuclear concentration. I may be wrong on that. But this brings up another related question Ė 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 didnít get any anyway; I donít 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 donít 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, thatís right. Thatís 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, Millsí Cross going on and Potts Hill, the hydrogen line work out at Potts Hill Ė 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 Ė 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 didnít.

Sullivan

What did you use for that?

Slee

Fleurs.

Sullivan

Iím sorry, yes. East-west arm of the Millís 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 donít 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 wasnít too sure some of those results were sound check it with the east coast arm of the Millís 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 Millís Cross itself is a pencil beam.

Sullivan

You had an entire Millís 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 Millís Cross system, the power response is proportional to the voltage response of each aerial.

Sullivan

Oh, thatís right.

Slee

You use an aerial fan beam in total power mode to get appreciably better resolution.

Sullivan

I must admit that pointís never hit me before, that you get better, yes, I see now. Okay. Now, thereís 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 Millís Cross, using the east-west arm.

Sullivan

Was this purposeful monitoring program and was there any theoretical impetus Ė any reason why you were looking for it, or just why not?

Slee

Well, I started the, actually, the Millís 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. Thatís when I published that paper, as a result of those observations.

Sullivan

Thatís 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 Millís 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 Earthís 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, itís only a minute of arc at the most. Itís rather smaller than the other strong sources around it in the sky.

Sullivan

But nevertheless, thatís 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, thatís 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 Millís Cross.

Sullivan

I see, and did you publish that in the late fifties?

Slee

Yes, it was published somewhere. It should be -

Sullivan

I donít 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, Iíve 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

Letís 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 donít think it was very rampant, not as far as I remember.

Sullivan

Well, Iím 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 donít think we came to any conclusions in the paper about that, did we? The possible mechanisms of radio emissions?

Sullivan

No, Iím 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, Iíd 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 werenít 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 weíd 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 Millsí 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 didnít 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 Bernieís?

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 havenít 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 dayís 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. Thereís a side lobe there.

Sullivan

Gone negative, yes.

Slee

Thatís 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: ďAn analysis of our results shows that there is no clear evidence for any effect of cosmological -

End Tape 86B

Click start to listen to the audio for tape 87A of the 1978 interview.

Begin Tape 87A

Sullivan

This is continuing with Bruce Slee on 1 March 1978. As I was saying, note: ďfor any effect of cosmological importance in the source counts.Ē Now, when I read that to Bernie Mills and I said to him, ďBut 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 thereís no cosmological importance to the counts that you have?Ē 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, wasnít he?

Sullivan

Right.

Slee

And he was expecting, so I think he was really saying that there were, thereís no evidence for any definite kind of evolution of the universe.

Sullivan

Well, I agree with you, but thatís a very important cosmological -

Slee

I agree.

Sullivan

Now, what he said -

Slee

Probably at the time, I didnít 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 wasnít clear that this could tell you about one universe from another. But I donít 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, Iím 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 donít 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, thatís true.

Sullivan

Iím 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 Ė ďIt is found that the two surveys are almost completely discordant.Ē

Slee

[laughter] Couldnít get a more definite statement than that.

Sullivan

No, indeed. Itís 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 wasnít 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 ďis the expected slope for a uniform distribution in a static Euclidian universe.Ē Now that doesnít 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 Iíd be interested, have you read Edge and Mulkayís version of this controversy in their book?

Slee

No, I havenít 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 donít 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 wouldnít 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 didnít 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 thatís a fair statement?

Slee

Yes, Bernie did.

Sullivan

Not as badly as Cambridge, but nonetheless, somewhat. It didnít 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 didnít 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, hereís 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

Thatís 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 Krausí detection, which indeed, that seems to be spurious now. There are other people who did not confirm his results. Was that using the Shainís Mills Cross?

Slee

And (?), wasnít it?

Sullivan

Oh, I see, yes both of them Ė 20 and 85 megahertz, right. They were right parallel of each other, is that correct?

Slee

Yes, thatís 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, Iíd 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 youíll 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 wasnít 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 wasnít as large as the (?), so the effective area wasnít 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, heíd 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 donít 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 donít think I was very surprised.

Sullivan

What sort of upper limits Ė 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, thatís 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 í62 Ė 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 hadnít realized it hadnít been published.

Slee

(?)

Sullivan

I have talked to Scheuer and he told me about that; I didnít realize it wasnít published.

Slee

What did he say about it?

Sullivan

Well Iím afraid I canít 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 donít know how it came about. I canít 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 canít think of anyone.

Sullivan

I canít think of anyone myself. Very interesting. Well, thank you very much. Itís been very interesting. This finishes talking with Bruce Slee on 1st March 1978

End Tape 87A


Modified on Tuesday, 27-Sep-2016 16:53:36 EDT by Ellen Bouton, Archivist (Questions or feedback)