Interview with Frank J. Kerr on 25 February 1976

Sullivan: 00:00

So this is talking with Frank Kerr, part three on 26th, February '76 at the University of Maryland. And would you just say again what you said about Westerhout’s reference to your trying to detect the galactic plane during the War?

Kerr: 00:21

Okay. Something about 1944, I guess, we're sort of trying to put together some radar type equipment with the Yagi and the 200 megahertz receiver, in those days, 200 megacycles. And it didn't really come to anything because of the pressure to do something else before the job was complete, although I certainly started to get the equipment together and [crosstalk].

Sullivan: 00:52

Never really got it on the air. Yeah.

Kerr: 00:55

And however, at about the same time Ruby Payne-Scott and Pawsey tried out something on the roof of the lab building that could detect I suppose again about 200 megahertz emission from the Sun. Now they got a signal, but again, I believe it wasn't carried very far. It was just--

Sullivan: 01:17

This was before they knew of any detections of the sun. They just--

Kerr: 01:20

No.

Sullivan: 01:22

You heard about Reber's or Hey’s?

Kerr: 01:25

I guess it was after Hey’s results.

Sullivan: 01:28

Well, I could have to try to ask Payne-Scott about that.

Kerr: 01:30

Actually, Hey and Southworth. At least their results both came through to us during the war, and they came through on the classified network.

Sullivan: 01:40

And I still haven't gotten a hold of those reports, but I'm going to dig them up somewhere I want to see what they say. Okay. So let's skip ahead now to your non-radar work, which I guess begins with neutral hydrogen, but you tell me.

Kerr: 01:55

Well, I was working on radar essentially until 1950 when I went to Harvard for a year. This was an idea of spending a year with some astronomers. And I guess I learned something useful in that time. And it happened that during that year, the first detection of the 21 centimeter line was made at Harvard. That's by Doc Ewen. And I was right there at the time. And so that was quite interesting. And actually van de Hulst was there too.

Sullivan: 02:38

Yeah. I've talked to him about all of that, so. Heard a lot about that.

Kerr: 02:42

And so we heard the news on the morning of March 25, 1951. And as they both together went from the observatory to the physics department, and they spoke to Purcell and Ewen. I saw the equipment again, we'd actually seen it before in a time that it wasn't doing anything. It wasn't receiving anything positive, I mean. And on that morning, Purcell was of course very pleased with the results, and he felt it wasn't really established well enough to publish straight away. And especially as van de Hulst and I were there, he suggested that we should send cables to our respective places to ask them to confirm it. Of course, the Dutch were just about there anyway, and so they were able to receive a signal also, a short time later, a few weeks later, perhaps two weeks later. Now in the case of the Australians, they had not started any actual work trying to find the hydrogen line, but they were a quite well-established place. So there was a lot of equipment around. And Christiansen and Hindman were given the job by Pawsey of trying to do that. And so at Potts Hill in a trailer using broadside array, I think it was, that had been used on solar work. In that trailer, they lashed together a 21-centimeter line receiver in six weeks, and they detected the line also. That's the reason for the joint publication by three places.

Sullivan: 04:50

And then Purcell held off until that detection.

Kerr: 04:54

There's an interesting sideline to this and something that has happened just recently. I got a letter from Bart Bok about a week or 10 days ago, and it was really in reply to a long one I'd sent to him on other matters. But he said that he'd heard that Purcell and Ewen were planning to run a 25th-anniversary celebration at Harvard this year, and he wondered if I had been invited to it yet. I have not by the way, but I don't know if it's really carried through very far just yet. But the interesting sideline point I was going to make was that Purcell was in a bit of a quandary as to who to invite to it from Holland. Because Oort has never admitted in print that Ewen and Purcell made the first discovery. So after 25 years, things are still slightly patchy there.

Sullivan: 05:57

Hopefully.

Kerr: 05:58

If you don't mind, I'll open this door so I [inaudible].

Sullivan: 06:01

Okay.

Kerr: 06:06

So that was March 1961. And I got back to Sydney, I suppose around September or so. And by that time, Christiansen and Hindman had carried out their first quite quick survey of they started Milky Way. Came out in the paper in the Australian Journal [of Scientific Research]. And at that time, or in that whole period, Christiansen's main interest had been in the sun. So he just wanted to divest himself of the 21-centimeter stuff and get back to the sun. And so I came into it largely because I'd been involved and I was interested in that anyway. And so I joined forces with Hindman and we started towards setting up with some rather better equipment. The first antenna, as I said-- I think it was a broadside array. Yes. So I think that antenna was really about 15 feet diameter, but there's a picture of it in the Christiansen and Hindman paper in the Australian Journal, 1951, anyway. So we set to, and had built for us a 36-foot dish. It was built by the people at the Lab. It was set up at Potts Hill, which was a place belonging to the Water Board in Sydney. It's where Christiansen already had his solar stuff and where the first prototype Mills Cross had been tried out. And so we set up a 36-foot dish there. That was a transit instrument. And it was sort of rough and ready in the way it was made, but it proved to be quite useful. And we had four channels, hadn't we? In our receiver.

Sullivan: 08:16

It was four times more than some other people had.

Kerr: 08:19

Yes, true. Of course, the Dutch, when they started, had one channel, but they tuned that right across the band slowly. We thought we'd improve a little bit and have four. And because it was a transit instrument, of course, all the observations were taken by just allowing the sky to drift past. So there were constant declination scans on these four channels, and then we'd move across the following day through a shift of three channel widths and so on until we crossed the whole band. And after we got this working, we probably looked at the Magellanic Clouds, to begin with.

Sullivan: 09:07

Well, that was your first thing to look at. I see.

Kerr: 09:09

And sure enough, we had a very nice surprise, especially in the Small Cloud. We found that the profile was much stronger in its high brightness temperature than we expected, considering that the Small Cloud at that time was supposed to have no dust in it. And so we assumed we've made a wonderful discovery of a place with a quite different gas-to-dust ratio.

Sullivan: 09:42

Were you expecting to detect probably both of them when you started out, or did you really have no idea?

Kerr: 09:49

I don't think we had too much idea, but we thought we should see it in the Large Cloud anyway because there is known to be dust there. Actually in both Clouds it was rather stronger than expected. And also we soon found that there's a lot of stuff in between the Clouds where there are no stars known to belong to the Clouds.

Sullivan: 10:11

Now, this association with dust, that really wasn't established at that time for 21-centimeter emission, but just on basic optical arguments about gas and dust going together or based on optical studies. Is that correct, or?

Kerr: 10:24

Well, it depends exactly what you mean by it not being established from your earliest studies at that time. It was not established in detail, I suppose, no. But I think everybody expected that, there was a basic expectation that the gas and dust would go together in approximate proportionality.

Sullivan: 10:49

Both confined to the plane, of course, and so forth. Yeah.

Kerr: 10:52

And there was never any surprise to anybody when the correlations between gas and dust were shown. I guess two or three years later, really. So this business of an apparently different gas-to-dust ratio in the Small Cloud was quite interesting. And of course, also the very large envelope of hydrogen all around the two and then apparent bridge across between the two Clouds. And then we also went on and in cooperation with de Vaucouleurs at Mount Stromlo, studied the kinematics and they showed that the Large Cloud was very different. It was rotating and we could get something about the mass of mass distribution--

Sullivan: 11:45

Further out than optically. It could be done, or?

Kerr: 11:48

Yeah. So, well, not so much further out, just it was better data because it was more smoothly distributed over the whole object and we had more kinematic--

Sullivan: 12:00

That was de Vaucouleurs and you I think in '57 or something like that that it was published. It was somewhat later than--

Kerr: 12:07

I think '54, '55, that sort of region. I guess about three papers, so maybe in '56, the last one. And it was more about the rotation was not so certain because we couldn't see the turnover properly. But I was given a rotation-type treatment, anyway, and got something out on [mass limits if nothing else?]. And then, let's see. I suppose around '54 or so, we finished our observing on the Clouds and really were going properly on the galaxy. And then right around the galactic plane with our business sort of cutting across on [inaudible] declination lines. And thus carried out the first real survey of the southern galactic plane region.

Sullivan: 13:12

Was this coordinated with the Dutch at all?

Kerr: 13:14

Well, it was distantly to begin with. The first real coordination occurred in '57, when I went over and spent a few months at Leiden.

Sullivan: 13:26

Yeah. We'll hear about that later I guess shortly.

Kerr: 13:29

But it's only rather distantly coordinated. Except that Oort was writing, I suppose, [inaudible] the Milky Way side should be finished. Because he had no interest in the Magellanic Clouds. He was interested to see [inaudible] worked out.

Sullivan: 13:52

And you were the only ones doing hydrogen line work in Australia. Is that right?

Kerr: 13:55

Yeah. That's right. And so, we got cracking on it. That was '54, '55. And I guess completed everything by '56. I can recall a special meeting we had in Sydney when Bart Bok first came out. He came out on a preliminary visit, really. He'd been invited to take over the directorship of Mt. Stromlo, and he came out on a short visit, I guess for a couple of weeks. And establish contact and work out what he thought needed to be done. And on his way through, he stopped off in Sydney and visited us at the Lab, and we went on to the Symposium. And I know I presented our first spiral diagram and our first evidence for the bending of the plane on both sides. And he was terribly enthusiastic about it.

Sullivan: 15:00

And both sides made the-- but not [inaudible] thinks of as the northern side?

Kerr: 15:06

Well, what I mean by that is, this was the first observational evidence for the bending on the southern side and [crosstalk]--

Sullivan: 15:17

Bending at two sides.

Kerr: 15:19

And the first interpretation of the two sides as a single phenomenon. At the time when it was observed in the [batch?] results, it was just a quaint phenomenon you couldn't do anything about. It needed the two sides for it.

Sullivan: 15:37

Now, in your survey, were there any different twists in the Dutch survey, or was it pretty straightforward as to how to carry out the survey and all the difficulties were in the interpretation?

Kerr: 15:48

Well, the principal difference was in the use of [inaudible] declination scans.

Sullivan: 15:54

But that was forced upon you more or less.

Kerr: 15:56

Yes. And so we had to put together a series of four channel scans and build those up into a common thing. Otherwise, I suppose we covered the same sort of country.

Sullivan: 16:19

Yeah.

Kerr: 16:20

And because we were doing constant declination scans [and if those lines?] were inclined to the galactic equator, which made it most likely more complicated.

Sullivan: 16:33

Yeah, pre-computer days. Now I'm a little bit hazy and almost embarrassed to admit I don’t know exactly where this stuff was published. I know about your paper in Monthly Notices, and Oort and Westerhout.

Kerr: 16:42

Well, It first results [inaudible]. There are two or three short papers. There's one that was published by Kerr, Hindman, and Carpenter. Martha Stahr Carpenter was with us.

Sullivan: 17:04

[Whole thing?] in Nature.

Kerr: 17:05

Yeah. That's the-- at first, I think it was rather similar to-- a [seminar?] presentation to that is [inaudible] [Bart Bok?], although the very first one of all-- because Bart was so enthusiastic, he took back, or I sent it to him after he went back, a paper about the twist in the plane that was in AAS meeting in the following Christmas. And Bernie Burke presented a paper at the same meeting because he had gone far enough south in his observations here in Washington [inaudible] recognize the symmetry involved.

Sullivan: 17:59

[inaudible].

Kerr: 18:00

The two sides-- in other words, this one with Patty Carpenter-- she's called Martha Stahr but her nickname was Patty. And then, the sort of archive thing is in the Australian Journal and published by Kerr, Hindman, and Gum.

Sullivan: 18:26

It was pre-- what year was it?

Kerr: 18:30

It would've been around '57. That's Colin Gum. Then Colin went on and worked out the principal plane in the galaxy from our results and the [inaudible] results. First of all, I should say, when I did-- in '57, I was at Leiden from the end of June and up to December, carried over all our raw data and did a lot of work, again, pre-computer days, in working out the spiral pattern according to the ideas that existed at that time. The principle difference between our two ways of working was that I considered the Dutch had over-restored the data, in the sense in which the word, restored, is used in radio astronomy, to try and get back [inaudible] finite resolution. And we in Sydney had gone through a long history of that from the Bolton and Westfold days that is--

Sullivan: 19:59

And Bracewell.

Kerr: 20:00

--and Bracewell and so on. And so I was in the [environment?] in which you then tried to put back too much. But they hadn't quite gone through all that. And so they had tried to restore for the finite bandwidth primarily, really slightly for the finite [inaudible].

Sullivan: 20:16

For the-- can't remember the name of the-- the edge of [inaudible] for the--

Kerr: 20:23

The tangential [crosstalk]-- Yes. Yes. They fitted models and so-- which were interesting, but they're only one possible case out of a continuum. And so a certain amount of arguing about that, but they accepted the idea that it could be done differently. So that map looks different on the two sides because of the different restoring mainly.

Sullivan: 20:53

Well, it was different methods, but I don't quite see what you mean by looking different on two sides, meaning that discontinuity in [crosstalk] or--?

Kerr: 21:00

It looks different in character.

Sullivan: 21:02

I see.

Kerr: 21:04

And many people have interpreted it as meaning that that's had more detailed observations [crosstalk]--

Sullivan: 21:14

I'll have to look at that again. Hadn't noticed that.

Kerr: 21:16

Yeah. And then--

Sullivan: 21:18

But let me ask you something. Why was that paper in Monthly Notices? It's a very interesting paper, but it's not-- it's a review paper more, a compilation sort of thing. Why was it not done up as a normal sort of journal paper?

Kerr: 21:33

Well, Oort had the invitation to write a review paper for them. That's the kind of stuff that was written very much in the Quarterly Journal in these days. And because he had that invitation, his stuff was put out in their [inaudible].

Sullivan: 22:00

He used it as a vehicle. And therefore, the meshing of it and all never got written up properly, so to speak, really, the way that map was produced.

Kerr: 22:11

Strictly speaking, yeah.

Sullivan: 22:13

As much as-- as much circulation as it's had.

Kerr: 22:15

Yes. That's true. In our own stuff on the southern observations only, we also didn't write in very much detail because we were giving sort of prior publication and things in Nature, that style of publication. And so it wasn't, as you say, ever written up in full detail.

Sullivan: 22:41

That's true. Another thing just popped in my head going back to Christiansen Hindman survey, to be frank, I was unimpressed with it from an interpretational point of view. I guess the point was that they missed completely what you could do with the kinematics.

Kerr: 22:59

Yes.

Sullivan: 23:00

They just plotted brightness versus longitude. Was this – Christiansen, of course it wasn't his game at all, I mean, and Hindman I guess, of course, well, it was new to everyone. I mean, was this all it was that they were novices and in terms of galactic structure, whereas you--.

Kerr: 23:09

Yes. They were completely out of it in galactic structure and they didn't really know anything about it and--

Sullivan: 23:30

Unfortunately, they didn't hook up with somebody that did, perhaps at Mt. Stromlo or something.

Kerr: 23:33

Yeah, I guess everybody was keen to get something out quickly. And at that time in radio astronomy there was a great tradition for publishing results, but sort of fairly raw without too much interpretation. Because most of early people [inaudible] were not astronomers.

Sullivan: 23:56

So skipping back to the survey, what would you say were the primary results of the survey? The downturn and then the interpretation of the warp of the galaxy, both sides? And what else was--?

Kerr: 24:11

Well, I guess the question of delineating the southern spiral structure for the first time. And the difference in the velocity patterns on the two sides of the sun’s center line is the other important thing. That too, it took a while to convince that that was real. I was skeptical.

Sullivan: 24:41

Of your observation?

Kerr: 24:42

As skeptical people. Well, at that time, perhaps still, they're skeptical of everybody else except for that.

Sullivan: 24:52

But are you referring to the northern and southern rotation curves?

Kerr: 24:55

Yes. Yes.

Sullivan: 24:56

Or that's one way to interpret it anyway.

Kerr: 24:57

Yes.

Sullivan: 24:58

All right.

Kerr: 25:01

But if you compare the places where the two sets of observations overlap, the agreement was pretty good. So it was clear that the result was probably okay.

Sullivan: 25:14

Yeah.

Kerr: 25:16

Now, however, the real proof of perhaps didn't come until a Parkes survey some years later in which the rotation curves on the two sides were done at the same place, the same techniques and everything.

Sullivan: 25:32

Yeah. One is always suspicious when they're separate sets of data and they give different answers.

Kerr: 25:37

Yeah. Perhaps that kind of attitude is stronger amongst optical people, because they've had their fingers burned pretty often in the past. I think on the whole radio people are more inclined to accept other people's results, at least they were in the old days. So that you assume that the results are going to match together unless somebody proves otherwise. Optical people perhaps take the other point of view. They need convincing, do it themselves. Two surveys go together.

Sullivan: 26:16

Now, was your total time pretty much devoted to this survey? I mean it is a gargantuan sort of thing.

Kerr: 26:22

It was during that period sort of. Well, a [inaudible] survey, [inaudible] galactic survey, essentially took most of at a time between '52 and '57. And then after I came back from Leiden in '58, or at the end of '57 or the first weeks of '58, I guess then I was getting rather much involved in the planning for the Parkes dish. And because of my interest in high frequency line, high frequencies as it was then, I was one of the few in the place that really supported Taffy Bowen and Joe Pawsey. And that was a period when he had his rows with Christiansen and Mills.

Sullivan: 27:29

You've told me about these.

Kerr: 27:30

And eventually. But I was keenly in favor of it. And thus was involved in the planning and spent a lot of time in assisting and preparing publicity and cases. Well, even in '56, actually, some of my time in '56 went into preparing a sort of propaganda booklet which we used to sell the idea to the government and the foundations over here. And then in the period '58 to '60, there's a lot of work. At the Sydney end, we had a sort of users committee and I was chairman of that.  And we spent a lot of time corresponding with the telescope designers who were in London and our representative over in London was Minnett, Harry Minnett. And we put a lot of effort into trying to make the telescope as good as possible for the potential users.

Sullivan: 28:43

Good interface, as we say nowadays.

Kerr: 28:45

And that, I believe, is one reason why the telescope has been successful for so long. Because we anticipated some things. For example, it was because of our suggestion and insistence from Sydney end that they changed over from analogue displays to digital display system.

Sullivan: 29:06

Which was unusual at that time. Yeah.

Kerr: 29:08

So probably the first time it was done, but that made a great difference in the convenience of operation of the system, and that meant that the control desk system has essentially lasted unchanged until now.

Sullivan: 29:25

Yeah, and before you did tell me about the development of the Parkes dish and so forth, so we don't need to repeat that. But I was wondering what you thought about what unique aspects were there-- Well, I just figured that the question I'd like to ask is why was the Australian government not willing to support it to the full extent when radio astronomy had been so successful in Australia? So you had to get American money?

Kerr: 30:00

Well, I guess because the amount of money involved was so high.

Sullivan: 30:03

For a small country.

Kerr: 30:05

According to the standards at that time, nobody had ever thought of spending that much money on a telescope or a single project.

Sullivan: 30:14

Was it much more than the Jodrell Bank [inaudible]?

Kerr: 30:16

No, it was probably only a little bit more. But the Jodrell Bank people were known to be in difficulty, financial difficulties, and no other comparable, and no other big telescope, optical or radio, at that time had ever been built at that sort of price, I think by any government.

Sullivan: 30:45

It had always been a foundation or something.

Kerr: 30:48

They've been foundations or private money building the 100 inch or 200 inch and so on. But it's not quite so simple as to say, I say, why didn't the Australian government spend it? I think at that time there was no tradition towards it, and so it was much harder to convince them at that time than ever would've been since.

Sullivan: 31:10

Yes.

Kerr: 31:11

And I guess also at that time there was quite a bit of contact with foundations in some other activities too. So it was quite reasonable.

Sullivan: 31:33

Yeah, sure.

Kerr: 31:34

Extension of the climate of the times.

Sullivan: 31:35

Well, during this period, were you able to do any scientific research? Were you pretty much working full-time on the dish and so forth?

Kerr: 31:48

I guess I didn't do very much new observing at that time, but, well, we were involved in the galactic coordinate business part of that time.

Sullivan: 32:02

That's right.

Kerr: 32:04

And a couple of other smaller discussion type papers, and the interpretation of the hydrogen line results and what they might mean, but nothing really large scale.

Sullivan: 32:19

Well, that was large scale, getting that dish going.

Kerr: 32:23

Yeah. And then when the Parkes dish started up, I spent a lot of the first year in a way attached to the telescope as one of its first users and “experts” in quotes. And got used to the system fairly quickly and cooperated with some other people in getting projects started. For example, I had some time on a flare star project. It was in the sense of being a friend of the telescope, helping somebody else get involved. And there were two or three other such projects that I was involved in as, well, a friendly outsider.

Sullivan: 33:19

Was this after Lovell had detected a couple?

Kerr: 33:22

The first star case was after Lovell, yes.

Sullivan: 33:25

Right. And who was the person that was doing this primarily?

Kerr: 33:30

That was Bruce Slee and Charlie Higgins, I think even way back--

Sullivan: 33:35

Oh yes. Slee and Higgins. I think I do, I remember.

Kerr: 33:38

And I was involved in the start of a project at Eric Hills on a continuum survey. Then gradually got involved in more 21 centimeter work, starting certainly by '62, perhaps late '61. And once the equipment was going, we sort of divided the field. And I was concentrating on the galaxy, Jim Hindman on the Small Cloud and Dick McGee on the Large Cloud.

Sullivan: 34:19

I see.

Kerr: 34:20

In fact, often the observational sessions were combined.

Sullivan: 34:25

Yeah.

Kerr: 34:26

And we'd go right around the 24 hours have two or three of us.

Sullivan: 34:35

Your interest it seems has been largely in surveys. Does that come about because of the nature of 21-centimeter work or just your own personal nature that you like? I mean, and some people think in terms of surveys, there are different styles.

Kerr: 34:50

Yeah. I suppose some of each. I've always been sort of unimpressed by the quicker, nasty papers that people try and get a quick result overnight and publish it straight away. And it may or may not be right. So I suppose it's partly my nature.

Sullivan: 35:15

And this Parkes survey began then very soon after the telescope got started. And for how long were you observing?

Kerr: 35:24

I guess the galactic Parkes is the longest of these three. They kept up until sometime in '66, not long before I came over here. And then in fact, when we came over here, we carried with us a lot of stuff that had only been half-digested up to that stage.

Sullivan: 35:52

Which I well remember, although I was never directly involved. Now, what would you say were the primary results from this Parkes survey that had not been known before?

Kerr: 36:05

Well, I guess that it could not do anything as dramatic as the discovery of the twisted edge of the galaxy or the different rotation curves. There's more a question of--  making more definite and believable the kind of things that had come out of our earlier survey. And then giving more detailed results for people to compare with other kinds of observations.

Sullivan: 36:39

When you talked about locating arms by the kinematical method and so forth. Now actually going back to the first survey. At that time, how much faith did you have in it that you really were tracing out real structure?

Kerr: 36:52

I suppose very early on people probably had a great deal of faith in it, everybody involved in it too. Though certainly we recognized that there was uncertainty because of the velocity dispersion that there was a 10-kilometer per second velocity dispersion on top of everything. So that all velocity, that the distance conversions were limited by that. And especially if you consider the region around the tangential points in which you're looking over a fairly large line of sight, and so that it gets smeared out by the distance through the galaxy, as well as being smeared out by the station. I guess that was recognized quite clearly, but that was disregarded as a smearing out of things. The question of really systematic, non-circular velocities was not thought of early, I'm sure, by anybody.

Sullivan: 38:03

Yeah. And what about the question of—what’s now called velocity crowding? I mean, interpreting bumps in your profile and temperature as really density concentrations?

Kerr: 38:20

Well, the phenomenon of velocity crowding was recognized right from the start. If you look at the equations in the first Dutch papers, the appropriate terms are there, that the brightness temperature depends inversely on the gradient of the velocity of distance. And so to that extent, it was certainly recognized, but nobody ever considered the possibility that the feature could be entirely due to velocity crowding. It could be sharp enough or the temperature increased through velocity crowding. But the possibility which people tend to talk of now, of an entire single feature being there only because of velocity crowding is certainly not [inaudible]. And of course, the density wave theory was still way in the future.

Sullivan: 39:23

Yeah. That's post my history anyway. Yeah.

Kerr: 39:26

I think one of the things people were very interested in at that time was looking at the tangential points as seen on 21 centimeters and comparing those with the steps in the continuum, which also gave tangential points, so to speak. And you could get similar evidence [into the closest?] spiral arms optically. And so that was one important thing in those days. In fact, I think it's discussed in that Monthly Notices [inaudible].

Sullivan: 40:06

Right. Mills's [inaudible] is the continuum in the primary source. Is that right?

Kerr: 40:11

That's about '58 or something.

Sullivan: 40:14

Yeah. Well, we're about up to '65 or so. Is there anything else that we've skipped over in your own personal field or any other comments you'd like to make about the development of radio astronomy?

Kerr: 40:30

Well, I guess the Magellanic Cloud work in the '60s from the Parkes station is interesting too.

Sullivan: 40:41

And I'll talk to them about that.

Kerr: 40:42

And how also at that time, sort of '64, '65, and so on. I said earlier I had been slightly connected with Eric Hills, the starting of the continuum survey, 21 centimeters. In ‘65, a continuum survey at 11 centimeters was started, and the first section of that was done by [Maxden?] Beard and myself within 10 degrees stretch of the galaxy. And that was a sort of a pilot study also in which we developed the techniques. I was in it as the astronomer, I guess, and he was in it as the engineer who was becoming expert in computing. And between us, we established what was probably the first really computerized continuum survey.

Sullivan: 41:59

I see.

Kerr: 42:00

Now that was only a 10 degrees strip and has been carried around. It has been carried around the whole region observable from Parkes since then in a series of strips and the whole thing is covered. And now they're doing a six-centimeter survey with Ray Haynes mainly involved, and it's more highly computerized still. In our survey we did not control the telescope by the computer, it's just computerized data reduction. But now, the computer controls the telescope as well. Also in that time period, I was interested in a continuum study of 11 centimeters of the Carina Nebula. That was one of the early ones where the comparison was made between radio and optical studies. In that kind of situation, you can use the comparison between radio and optical to see if a dark region in a nebula is due to foreground dust or whether it's lack of excitation. And Carina Nebula is interesting from this point of view because there are three dark regions running into it and the comparison of the radio and the optical showed that of these three, two were due to dust, and the third one was due to lack of excitation because the radio was present in the first two, but not in the third. Now that method has been carried much further by many people. I think this was one of the first--

Sullivan: 43:54

About what time was this?

Kerr: 43:56

About '64.

Sullivan: 43:59

What about the possibility of other spectral lines? You were always working with the hydrogen line. Did you ever think about looking for some other ones, or?

Kerr: 44:07

A small amount of thinking was done and I guess we kick ourselves now that we didn't do any more on it. And perhaps, well, we were conscious of a couple of papers on. There big one by Townes, and I think one by Shklovsky. And also a fellow called Yardley Beers was there.

Sullivan: 44:38

You told me about this compilation he made. I'm going to try to get a--

Kerr: 44:41

And spent a few months and--

Sullivan: 44:42

Copy of that.

Kerr: 44:43

He's got a compilation there. It was interesting, but nobody ever really followed it up too much, I'm afraid.

Sullivan: 44:51

No one ever looked for OH in Australia. I mean, there were a couple of attempts by Barrett.

Kerr: 44:59

Yes. We heard about those.