Interview with John G. Davies

Begin Tape 113A

Sullivan

This is continuing with J.G. Davies on 11 August, 1978. This question of -

Davies

Twelfth.

Sullivan

Twelfth, yes. This question of the origin of the meteors, could you go into that? How did the problem come up?

Davies

Well, it came from the optical observers, and there were two sets of optical observers who had made measurements of the velocities of meteors by various techniques, estimating the speed across the sky and the distances. One of these was Öpik, who first in Estonia and then in Northern Ireland, had a technique which indicated that many meteors were moving much too fast (?) the solar system and had hyperbolic orbits. Then there was Hoffmeister at Sonneberg from Eastern Germany who had the opposite view.

Sullivan

Were they using different techniques?

Davies

They had differing techniques, they both sounded good, but one had a locking mirror, and you saw the meteor path through and this sort of thing as you looked down - and optical effects, physiological effects, I suspect. There was no photography, direct photography wasn’t possible. And made this suspect. Now we therefore set out to measure the velocities, and if we could get directions as well, then this was even better, but initially only velocities with more directions. You had a narrow beam, the meteor had to be perpendicular to that beam, one but not two dimensions, coordinates for its direction. And using that technique, we could find no evidence for more than (?) observational errors over the limiting, parabolic velocities.

Sullivan

Which is what, 45?

Davies

42, relative to the sun, but then the earth has a velocity of 30, so -

Sullivan

Right, so you had to take that into consideration.

Davies

You get there if they are moving in opposite directions, but you have to set the (?) per second, but you knew the direction of the earth’s motion, and you knew the direction you were looking, so you could do some geometry on it, of course. When we had the three station system measuring actual directions as well as velocities, then of course, we could measure the orbits of individual meteors. And still, as my thesis was on -

Sullivan

Oh, I see, you did a thesis at Jodrell.

Davies

My thesis, was at Jodrell, was on meteors.

Sullivan

And when was that awarded?

Davies

1951-52, something like that, I don’t know. The conclusion certainly was that there was no evidence for a significant proportion of hyperbolic orbits – we measured a thousand or something like this, and none of those were any marginally beyond experiment errors.

Sullivan

Were you in contact with Öpik and Hoffmeister?

Davies

Yes, both of them. As far as one could communicate with Eastern Germany, of course. Öpik was a difficult character in some ways. Hoffmeister was a nice chap, I have gone over and have seen him, he’s dead now, but I met him over there. We got on, we had communication with both of these. We also had active communication with an amateur group in England led particularly by Prentice, who were making optical observations, and indeed they would often come to Jodrell and make simultaneous observations so we could relate the meteor echo with the particular visual characteristics, and this was very important.

Sullivan

Now what did Öpik and Hoffmeister think? Did they visit Jodrell themselves actually in these days?

Davies

Öpik certainly did, Hoffmeister never.

Sullivan

Did he sort of look around and “harrumph” and say, “Well, this is not astronomy,” or was he seriously trying to figure out exactly what you were measuring?

Davies

I think that Öpik was quite an old chap by then, and he’d had a very hard life. He’d lost all his records in getting out of the East, and he never really accepted that our measurements could be good. We must be missing it for one, and he searched for methods of saying why we were not seeing the many hyperbolic meteors which had to be, according to his theory.

Sullivan

Oh, I see, you were missing them.

Davies

We were missing them somehow. He didn’t say we weren’t making a good observation.

Sullivan

And did he publish this sort of argument also?

Davies

Yes, he must have, I couldn’t cite it though.

Sullivan

What about other optical astronomers, or I guess since you were just in meteor radar -

Davies

There was a conference in, must have been 1949, in Manchester. I guess It’s been published in Reports on Progress in Physics.

Sullivan

I see.

Davies

Which Öpik attended, I remember this. On meteors. I think you’ll find something there.

Sullivan

Ok, I’ll check that. Now, of course, you must have been educating yourself all this time in astronomy.

Davies

Oh yes, oh yes.

Sullivan

How did you do that? Just reading materials, or —

Davies

I suppose partly. We are, of course, part of the Physics Department in Manchester, and in those days under Blackett’s direction. He supported us very greatly and of course, the department was expanding rapidly after the War, which gave great opportunities. And it was not long after that, a year, I can’t remember exactly when, when the chair of astronomy was established there. Largely it was the idea that it would support the work going on at Jodrell Bank. And so we had in the early days, we had many lectures from Professor Kopal, who took up that chair -

Sullivan

Oh, yes.

Davies

(?)

Sullivan

Was he in the physics department actually?

Davies

He was an astronomer, oh yes. Originally in Czechoslovakia, then he’d been in the States for some time and he was first optical in that chair and still is, in fact. And he taught us basic astronomy – very well, too.

Sullivan

Now, as you look back, in the late forties, when there was a group, I guess, a staff of ten or something like that?

Davies

I suppose so, yes.

Sullivan

And then, of course, in the early fifties Hanbury-Brown came and others and there were more students, did the nature of the place change, would you say?

Davies

Oh yes, it must obviously, as it grew, and grew more permanent, it changed somewhat, but -

Sullivan

How would you characterize the important changes?

Davies

Well, in the early days if you wanted to do an experiment, or a student was going to write his thesis on a particular thing, you would spend the first year building the equipment, and then you’d do an experiment. As time goes on, of course, you get more and more of the equipment given to you, which has some advantages and some disadvantages as well. Some students never understand what the equipment does, but that’s an inevitable feature.

Sullivan

Was this process already beginning in the early fifties, are you saying, or was that somewhat later?

Davies

Yes, it was. Because even a meteor radar is a fairly complex thing, and parts of that were given. For example, the precise recording technique required for producing the diffraction patterns that I was interested in had to be developed, and so on.

Sullivan

A question which we haven’t touched on is the origin of the equipment that you did have in the late forties, was it all military surplus?

Davies

Yes, it was military surplus – you could go out and buy a hundred kilowatt transmitter for ten pounds. Provided you towed it back yourself. And the receiver which went with it, which was through the actual equipment, was five pounds. I remember those figures quite clearly. It stopped them from being thrown down old mine shafts.

Sullivan

And how long did this sort of situation continue before you finally had to - ?

Davies

A few years, three or four years I suppose, only you could go on buying surplus equipment from stores for some time after that for a very cheap rate. And a great deal of our early equipment was built on that sort of basis.

Sullivan

But there must have been quite a bit of modification that you had to do for your special purposes, or is that not true?

Davies

Only in the recording. Well, in the control, yes, we made crystal control, pulse generators for example, because the pulse repetition rate was important to us. And the recording devices were special, but the basic equipment, and the telescope, the aerial system you used was special, too. We built a 210-foot parabolic telescope in 1950 with our own hands.

Sullivan

Right. But before we get to that stage, I mean, the earlier meteor radars, were they just once again, just adopted from military sources?

Davies

Oh, yes.

Sullivan

What exactly were they? Just Yagi rays?

Davies

Yes, Yagi rays were what we used.

Sullivan

Okay, so what was it that made the group decide, apparently, that more needed to be done than just meteor radar astronomy? What, would you say, was the thrust? Were you thinking that “We’d solved the problems,” or - ?

Davies

No, no, really the meteors dropped out because it became less and less compatible to try to do active and passive work on the same site.

Sullivan

I see.

Davies

For a long time, the meteor systems, we had several radars going simultaneously – they all transmitted simultaneously. They were all coherent, of course, so as to not interfere with each other. They also produced suppression pulses which suppressed the radio astronomy receivers. And of course, as soon as one started to think about sensitivity in this process, it obviously wasn’t a very sensible thing to do.

Sullivan

Time sharing didn’t -

Davies

Time-sharing didn’t, it got less and less useful, and so we gave that up. But even after that, I went on and did some work, my later papers were purely theoretical calculations on perturbations of meteor orbits and on generation of some rather extraordinary meteor showers. The Giacobinid meteor shower, which produced an enormous number of meteors for about ten minutes in several years, the latest one being in 1946. We were able to show it must have actually come out of the parent comet within about three or four months in, I think, about 1892.

Sullivan

I see.

Davies

We traced it back to an event which must have happened -

Sullivan

And this is an analysis that you did in the late fifties?

Davies

Yes, with (?) who was my student.

Sullivan

But now you’re implying that they, more or less, made you turn your transmitters off, and so you had to turn to theory at a certain stage? Or interpretation?

Davies

Well, by that time we were mainly on radio astronomy, and it was a sort of a lingering interest.

Sullivan

Is this the late fifties we’re talking about now?

Davies

I guess so, yes, late fifties.

Sullivan

In fact, I just talked with John Evans up at Helsinki and he told me about this conflict between the active and the passive people.

Davies

Yes. It went on with the lunar and planetary radar later, rather than the meteors.

Sullivan

A bit longer, yes. So it was a matter, really, that you were transmitting pretty much every day?

Davies

Well, this was survey equipment, yes. And without going continuously, -

Sullivan

It wasn’t just a matter that it was just a few meteor showers during the year and you were -

Davies

Well, there were meteor showers when we did constant observations, but much of the observations were survey.

Sullivan

And, of course, you discovered many new one this way.

Davies

Yes.

Sullivan

That, I think, once again, I don’t really know that much about that field, I think is one of the most interesting aspects of the whole radar and meteor field – just the ability to see the other half of the sky.

Davies

Yes, I think that is a good part of the story.

Sullivan

Well, maybe I should ask you, that and of course, the business about the solar system origin of the meteors which -

Davies

That was probably the best, the most important thing. I mean, the fact that there were meteors in the other half was reasonably predictable.

Sullivan

Yes, but you like to know where they are.

Davies

It was nice to know, yes. And they were somewhat different in character from the night-time ones.

Sullivan

I didn’t know that. How is that?

Davies

Well, the night time streams were mainly fairly good and concentrated things, you got a few days regularly; the summer daytime streams, as we called them, was a continuous procession that lasted May through July – three months and one radiant came and another one went, it, sort of, moved across the sky with the sun. An enormous area of activity which was more diffuse than the night time showers, and much more long lasting.

Sullivan

And concentrated in those three months?

Davies

Concentrated in those three months. It had peaks in it, of course.

Sullivan

Why is that – this annual effect?

Davies

Well, all meteor showers are annual in that the earth’s orbit had to intersect the meteor.

Sullivan

No, but I mean, -

Davies

Why in the summer?

Sullivan

Yes, why in those three months?

Davies

I don’t think there is a good reason for it; I mean, there is no such thing as, no similar thing in the Southern Hemisphere, in the Southern Hemisphere’s summer.

Sullivan

I see. You mean in their daytime showers?

Davies

Yes, they had some daytime showers, but they don’t have an enormous concentration, as we did, in their summer months, when a reversed annual effect would be expected as the ecliptic rises and sets in the sky.

[break]

Sullivan

What other important results would you think came out of this meteor radar work either in astronomy or in ionospheric physics?

Davies

I think the physics of the formation of the meteor trail and its recombination was quite important, and Kaiser, who is now at Sheffield, was the chief worker in that field – in fact, he still is.

Sullivan

And is it a fair statement to say that these main two astronomical results, once they were established, that the field sort of died out because it wasn’t clear what further direction to go – in the late fifties, I’m talking about.

Davies

No, the field did go on, not with us. Whipple, in particular, continued both in radar and photographic work. The satellite program using cameras kept making good photographic observations. And that led to actual information about what the meteor was, the sort of particles of which it’s made, of which rather little information came from radio, more from the optical side.

Sullivan

Right, but do you agree that the field sort of peaked in the mid-fifties or -

Davies

I think so, yes. I mean, it may be partly a personal view because of - But I think it is less important now, but we had a good time then.

Sullivan

Okay, well, let’s go back to the development of Jodrell Bank. The decision to build something like, for instance, the 218 foot non-movable dish, was a decision like this arrived at from a consensus of the group, or was it, sort of, one of the sub-group leaders decided he wanted it and then would go to Lovell and make his arguments?

Davies

It was a small group in those days. Not all the students would be involved in that, Lovell and Hanbury, I think, basically.

Sullivan

And why was there a need felt to do other than meteor radar work, which was pretty exclusively what was done in the late forties?

Davies

I think it was a general interest in expanding into astronomy, using radio techniques in astronomy. It was always there; we started in the meteors, certainly, but we rapidly moved over.

Sullivan

You mean simply that you saw that this was going on and that interesting results were coming out of it?

Davies

Yes.

Sullivan

Do you have any thoughts on why the Jodrell Bank approach tended to be more one of the big dish, not exclusively, but more so than the Cambridge approach where interferometry played more of a role?

Davies

Well, I guess, its partly a personality matter, but also, of course, that nationally you couldn’t support two groups doing the same thing, and by choosing different techniques we became complementary groups.

Sullivan

Well, in fact, Professor Lovell made this remark to me that it would be silly, to say the least, for him and Ryle to argue in these national committees.

Davies

Yes, well that was always true, and they came to external agreements about what they were going to do before they went into a meeting.

Sullivan

And supporting each other – “This year you scratch my back, and I’ll scratch yours,” type of thing.

Davies

Yes.

Sullivan

You were never involved in the lunar radar work, is that correct?

Davies

No, no.

Sullivan

Always in the meteors. What, as you look back on the forties to fifties era, what is it that made the radar work – well, you made one point about the conflict with the passive people – but was that what really made it fade out at Jodrell? The primary reason? What other reasons might there be?

Davies

I think that was the primary reason. It may also be partly chance, with those principally concerned, either leaving or in my case, I wanted to swing over to the other side.

Sullivan

You mean John Evans leaving, and the lunar radar?

Davies

Yes, and Greenhow and Kaiser and so on. They all went on.

Sullivan

And what did your interest switch to, and when did that happen?

Davies

Well, I’ve always had a technical interest as well as an astronomical one. I’m not too sure. I was always concerned with the construction of our large telescopes – I was responsible for the control system of the Mark I, which was an analog computer, and then with the digital control for the Mark II – I think the first large instrument which had an online computer attached to it.

Sullivan

Now, when was that?

Davies

Well, the Mark I was completed in 1957 and Mark II in 1963. Some four or five years earlier in each case was when it started.

Sullivan

But the difference in the time, was that a matter that many computers had become available on the market so that one could think about doing this?

Davies

Yes, yes. And you see the analog computer was entirely valves, there weren’t transistors when we thought about that. And you couldn’t envisage using a valve, digital computer, for the reliability problem.

Sullivan

I see.

Davies

So the analog system used many fewer valves, and was adequate and accurate.

Sullivan

You mean the one they used to control the Mark I, for example.

Davies

Right.

Sullivan

Of course, Professor Lovell has written a book about the building of the big dish and we don’t need to go into most of the dates and all, but I would be interested in your comments on what were the unique aspects of this design, and what were the basic problems that had to be solved as the design and construction went along?

Davies

Of course, it was the first structure like that, it was made sort of completely tippable. The engineers regarded it as sort of a bridge problem, with the extra dimension of motion added to it.

Sullivan

Well, in fact, Husband, were a bridge building company, but they felt that it was quite do-able?

Davies

Oh, yes. And after all, it’s specification was to work at a wavelength of one meter; in fact, we now use it up to about six centimeters.

Sullivan

Meaning that you had quite a bit of tolerance.

Davies

We had quite a lot of tolerance. In fact, it would not work mechanically if you made it as sloppy as the astronomical tolerance allowed. So it’s a better instrument.

Sullivan

What were the other considerations that had to go into the design, as far as compromises and so forth? For instance, the feed, the situation where you had to put your life on the line a little bit to get up there, seems to me a little bit strange.

Davies

Yes. Well, I guess we hadn’t sort of visualized the problem too much in the early stages, there were various schemes involved and they’ve changed, of course. It has changed quite a lot in the course of time.

Sullivan

Well, in the present version of the telescope.

Davies

Yes.

Sullivan

(?)

Davies

Initially, of course, for long wavelength there was only going to be an open dipole there anyhow, which required very little attention once you had somebody put it there. Now you have to have parametric amplifiers and cooling systems and so on.

Sullivan

Well, that’s true.

Davies

The situation’s very different.

Sullivan

Once you were only thinking of just taking the signal down.

Davies

That’s right, by cable, at least to the base, to the apex of the dish.

Sullivan

This had been done with the 218 foot dish.

Davies

Yes, the same idea. Right.

Sullivan

What about in the pointing control? Was there any particular problems?

Davies

No, I don’t think so. It was done with a sort of analog device, using magslip resolvers which produced sine and cosine voltages which were then multiplied and added and so on to solve differential equations. Odd problems, but I think if you go along on the surface and this sort of thing, but they’re less difficult to solve that way, I think, than a mechanical analog, which can actually jam up.

Sullivan

For instance, like the NRL 50 foot dish.

Davies

Yes.

Sullivan

That brings up another point, about the azimuth-altitude mounting. Were you at all bothered by thins, seeing as, except for the NRL dish, all previous dishes of any size had been equatorially mounted – of course, there weren’t -

Davies

There was nothing of any size, you see.

Sullivan

Yes, Dwingeloo hadn’t even come along.

Davies

Yes, yes. When you got to that size, an equatorial mount was, and still is, quite impossible.

Sullivan

But did this not bother you at all in terms of the disadvantages of the polarization characteristics and possible tracking difficulties -

Davies

No, no. Polarization was a secondary issue probably in those days, and tracking did not seem to be a problem.

Sullivan

Right from the very beginning. Why was it then, I still have difficulty understanding why, for instance, the 140 foot people, which came along many years after your experience, really thought they had to have an equatorial mount.

Davies

I don’t know – you’ll have to ask them.

Sullivan

Well, I haven’t gotten a good answer.

Davies

They had more engineering difficulties with that, of course, than we did.

Sullivan

Right.

Davies

Because of that, because of the equatorial mounting.

Sullivan

You think that was the basic problem?

Davies

No, I think it’s some and I think the whole bearing problem which they had would not have occurred with an alt-az.

Sullivan

Okay, well are there any other aspects of, in particular, your astronomical career, prior to 1960 or so, that I’ve missed? I don’t have, unfortunately, a bibliography for you. Important point, or important points, about the development of radio astronomy in Great Britain that you would like to tell me?

Davies

No, I don’t think there was anything else. Nothing startling comes to mind.

Sullivan

One final question. In 19-- well, let’s start in the early fifties and then say later on in the fifties, what would you have called yourself, if your neighbor asked you what you did?

Davies

Astronomer.

Sullivan

An astronomer?

Davies

An astronomer, first.

Sullivan

Even in the early fifties?

Davies

Yes, in the early fifties.

Sullivan

That’s interesting, because most radio astronomers, as we now call them, wouldn’t have answered that at that time. Was this because you were working so much in a field related to optical astronomy, perhaps?

Davies

I don’t think so, no. I’m surprised at your comment, actually. Maybe it was, I don’t think it was true in England, let’s put it that way. The optical astronomers had accepted us and did right from the beginning, you know, which was a little remarkable.

Sullivan

Accepted you in which sense? Listened to you at RAS meetings?

Davies

Yes, right. As members of the RAS, we got very full, any paper we submitted, we were asked to read as well, and this sort of thing.

Sullivan

Which were the key people, would you say, in the optical astronomy side, in Great Britain who welcomed in this new field? Because in other countries, there was not always this close cooperation.

Davies

Well, I wouldn’t want to mention names, because I think all of them – I don’t recall.

Sullivan

You don’t remember anyone particular who was -

Davies

I don’t remember anyone being against it.

Sullivan

I see. Okay, well, thank you very much.

Davies

Not at all.

Sullivan

That ends the interview with J. G. Davies on 12 August 1978.

End Tape 113A