Interview with Cornell H. Mayer on 30 September 1971
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The interview listed below was either transcribed as part of Sullivan's research for his book, Cosmic Noise: A History of Early Radio Astronomy (Cambridge University Press, 2009) or was transcribed in the NRAO Archives by Sierra Smith in 2012-2013. The transcription may have been read and edited for clarity by Sullivan, and may have also been read and edited by the interviewee. Any notes added in the reading/editing process by Sullivan, the interviewee, or others who read the transcript have been included in brackets. If the interview was transcribed for Sullivan, the original typescript of the interview is available in the NRAO Archives. Sullivan's notes about each interview are available on the individual interviewee's Web page. During processing, full names of institutions and people were added in brackets and if especially long the interview was split into parts reflecting the sides of the original audio cassette tapes. We are grateful for the 2011 Herbert C. Pollock Award from Dudley Observatory which funded digitization of the original cassette tapes, and for a 2012 grant from American Institute of Physics, Center for the History of Physics, which funded the work of posting these interviews to the Web.
Please bear in mind that: 1) This material is a transcript of the spoken word rather than a literary product; 2) An interview must be read with the awareness that different people's memories about an event will often differ, and that memories can change with time for many reasons including subsequent experiences, interactions with others, and one's feelings about an event.
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Sullivan
Now we start with Connie Mayer the same day [30 September 1971] at NRL [Naval Research Laboratory]. So tell me about the beginning of radio astronomy at NRL.
Mayer
I don't know what date things got started, but probably around 1946, and the first things that were done or attempted were [John P.] Hagen's attempted measurements of the Sun and Moon. I believe most of it was at 8 millimeters wavelength, and the early stuff was done with a 10 foot dish at that wavelength.
Sullivan
This is the 10 footer that’s still up there in the building?
Mayer
No. But one of those 10 footers came about that time, I mean early, not in 1946 I think- I don't remember dates. Certainly, one of those came early on a simple mounting. But anyway, those were the first things that were done and somewhere around 1948, [Fred T.] Haddock started doing things in radio astronomy.
Sullivan
What was the branch called then? It wasn't the Radio Astronomy Branch.
Mayer
Let's see, it was originally called Centimeter Wave Research and by that time the name had been changed, I think, to Radio Frequency Research.
Sullivan
And these were all former radar people from the war?
Mayer
Basically radar- what the branch did in the war was some work on radar systems, some work on testing and fooling around with operational systems, both in contractor tests and in operational type tests. And some work in development of special radars, submarine radars, and Doppler radars for getting actual ground speed tor aircraft. A large amount of the work was on components, and a lot of work was done in developing wave guide components and antenna components for centimeter wavelengths.
Sullivan
How did the connection with radio astronomy come about? Was it a personal interest of Hagen's or something like that?
Mayer
Yes, a personal interest. Anyway, that's how it got started. Somewhere along the line [J. E.] Gibson started working with Hagen on the 8 millimeter stuff and then somewhere around 1948, Haddock started doing some things, but nothing experimental. He was doing literature searches and learning about radio astronomy and doing some pseudo-theoretical things.
Sullivan
Did he publish any of that theoretical stuff?
Mayer
No, it wasn't that kind of theoretical stuff really. It was more like...
Sullivan
Feasibility stuff?
Mayer
Well, yes, that's why I hesitated to call it theoretical, but I don't know what else you'd call it. Just trying to see what sorts of things you could do. And of course, at that time people still thought everything was thermal radiation and so forth. But I guess in about, up until 1949 or 1948 everything was done with simple receivers. It wasn't very satisfactory at all, too much gain drift and so forth. In about 1948 Hagen assigned a guy named John [Dalke?], who was working here to build a Dicke radiometer, a copy of the radiometer that Dicke had used for the atmosphere measurements. And he did put one together, which didn't work, and about the same time, Hagen asked me to put together a total power radiometer for an eclipse measurement, which I did. It was essentially the same as the ones he’d been using- this was at 3 cm- the ones he'd been using at 8 millimeters- just a mixer and an IF followed by a DC amplifier and recorder. But it didn't work satisfactorily at all, I didn't think. By that time, [Dalke?] had given up on the Dicke thing, so I took over the Dicke thing and put together a 3 cm Dicke radiometer, which did work.
Sullivan
This was about what time?
Mayer
About ‘48. And that was used by Hagen for an eclipse measurement [Sullivan: May 1947] from a destroyer off the coast of Brazil.
Sullivan
Was this published in any form - NRL reports?
Mayer
I can’t remember. If it was published, it was in some not very legitimate way.
Sullivan
Was this the first radio observation of an eclipse? Do you know that? First that you know of anyway?
Mayer
I don't know that.
Sullivan
Might well be though.
Mayer
It was certainly one of the first. Well anyway, when this Dicke radiometer did work quite well, we started out right away to build a second one because Hagen wanted us to look at the Sun.
End of Tape 4A
Sullivan Tape 4B
Mayer
Then we put a 10 foot dish on the roof of the Building One. And that radiometer was used for several years to look at the Sun and the Moon. Numerous lunar eclipses were observed, and the Sun was observed fairly extensively. None of this was ever published.
Sullivan
What was the reason for the lack of publishing? It just wasn't in their tradition?
Mayer
Probably partly that. And probably partly that they were just expecting too much and we didn't publish just routine results, which probably should have been done but wasn't. Nothing happened that we could interpret as exciting or remarkable, so it just didn't get published. But part of it was just habit, too. Well, anyway, somewhere along about there, the Sun was being looked at in an attempt to measure atmospheric absorption at 3 cm. During the measurement, a flare occurred, probably a nice burst at 3 cm, which was the first burst observed at wavelengths that short. That was published.
Sullivan
This was what year now?
Mayer
I think it was about 1949, somewhere around there. [Sullivan: July 1948]
Sullivan
And where was it published?
Mayer
Physical Review Letters.
Sullivan
By whom?
Mayer
First author was a guy named [M.] Schulkin.
Sullivan
Sch?
Mayer
S-c-h-u-l-k-i-n. Well, anyway, somewhere throughout this whole period, too, Hagen and Haddock- I'm not sure which one got the idea first- started pushing the 50 foot dish. And as I remember one of the ideas for building it, the dish, or at least one of the justifications for building, it was for moon radar. And it got built somewhere along 1949. I think it was erected in about 1950. But it didn't really get started to be used for any significant radio astronomy two or three years later. In that intervening period- we skipped the 50 foot dish for a couple of years.
Sullivan
What was the reason for this delay? No suitable receivers?
Mayer
I'm not quite sure. Part of it, certainly, was that we were doing these other things that I was going to skip back to, and part of it was that it went through quite a long test and alignment period. And then it went through quite a long period where Hagen was trying to use it at 8 mm, which was all unsuccessful for a number of reasons, some of which maybe we'd better not mention
Sullivan
Was the surface partly to blame? Or is it that good?
Mayer
I think the surface was undoubtedly partly to blame. Well, what Haddock and [Russell M.] Sloanaker and I privately concluded later was that we didn't think they knew where they were pointing well enough. But they did point at the Sun and get some results on the Sun.
Sullivan
This is a former 16 inch gun mount, correct?
Mayer
Not 16 inch, it was a twin 5 inch anti-aircraft gun. Two 5 inch guns on one mount.
Sullivan
And what was the supposed pointing accuracy? What were the specs? I guess it must have met specs, or it wouldn't have been accepted.
Mayer
I don't think that's right at all. It wasn't a matter of accepting it. Again I wasn't in on this so I don't know the true facts, but I assume the reason for putting it on a gun mount in the first place was to save money, not having to build a mount. And I don't know what the aiming specs were for the gun mount as a gun mount, but I suppose they were pretty good. I don't happen to know what they were. But, of course, the way it was hooked up to point the dish was considerably different from that. That, we can get into a little later.
Sullivan
That was sort of a limitation, wasn't it, for that dish?
Mayer
Sure. But anyway, in the years, there were three major eclipse expeditions: To Attu in 1950, Khartoum in 1952, and [?] Sweden in 1954; and these were major efforts for a group of like four people. They certainly kept myself and to a large extent, Haddock, and to quite a large extent, Hagen, and to quite a large extent a couple of other people pretty well occupied full time, just getting ready for these things. You know, the logistics were terrible, going to places like that, you had to carry everything.
Sullivan
Now what was the purpose of these?
Mayer
The purpose was to try to get the radio brightness distribution on the Sun and the real specific thing you can point to is to prove limb brightening but the real underlying thing, of course, was to test out or help develop models of the chromosphere. This is what Hagen did for his thesis, was these chromospheric models. And of course, he had a very strong drive to get the experimental data to confirm or test out or whatever you want to call it.
Sullivan
What school is this?
Mayer
Georgetown. And so anyway- I don't remember now- there were different people brought in on different parts of things, but through that whole period, there was only like two or three or four people working on radio astronomy full time. There was some effort by some other people on a limited part-time component basis, but it was mainly just that kind of group, so these eclipse efforts were a full time job.
Sullivan
That's maybe why the 50 foot languished a little bit?
Mayer
That's one of the reasons. Well, anyway, somewhere in that period also, the hydrogen line was picked up and Hagen right away got interested in that and he ordered a hydrogen line receiver from [Harold Irving "Doc"] Ewen. And I don't remember dates...
Sullivan
You say order now, does that mean Ewen already had his company?
Mayer
I guess so, I'm not quite sure about that, but that's about the time the company came into being. But whether he had his company or not, he got it sold - two or three radiometers.
Sullivan
Right.
Mayer
I don't remember again the date this thing arrived, but it was probably somewhere around 1952 or 1953. But at that time Hagen brought McClain in to get that hydrogen line system going. McClain had zero interest in radio astronomy; in fact, he didn't even want to do it. He didn’t want to do this but Hagen had him do it. So really the first thing of any significance that happened to the 50 foot was that Haddock and Sloanaker and I finally got Hagen to let us put a radiometer in it. This was a 9 cm radiometer. He let us have a week.
Sullivan
What was it doing otherwise?
Mayer
Nothing.
Sullivan
Just a week off. What you were doing otherwise?
Mayer
He let us have a week on the antenna- I think it was a week. It might have been two weeks.
Sullivan
But I'm wondering why he was so stingy? Because he thought you should be working on other things?
Mayer
This shouldn't be on tape, but he didn't want anybody else to use it. It was the competition.
Sullivan
I see.
Mayer
I mean, that's my opinion, and I think it's right.
Sullivan
So you got a week on the antenna?
Mayer
We got a week on the antenna, and the first thing we looked for was H II regions. And we found 15 of them or something like that. And we also looked at the then-known strong radio sources, things like Cygnus A and Cas A and so forth at this wavelength. Previous measurements, I think, the shortest wavelength had been on some of those sources like Cas A, possibly 20 cm. But I’m not sure of that either. It might have been at a much lower frequency, but certainly nobody had found the H II regions. Anyway, after that week or two, whatever it was, the 21 cm continuum radiometer was put in and they looked at all these same sources at 21 cm. Different group now- this was [Edward F.] McClain and Hagen. And also looking at the strong radio sources, they found some additional H II regions. Then again I guess at about that same time, without looking at dates I don’t know, they got the line system working.
Sullivan
Well, before we go on to the line system, can I just clarify, first of all, had these H II regions been detected at lower frequencies before?
Mayer
No.
Sullivan
So that was the first there. What was the impetus to look at H II regions? Was it partly of these feasibility things that Haddock was doing?
Mayer
I suppose so. It was just an obvious thing to look at short wavelengths. It was known that they should be thermal sources.
Sullivan
Yeah, 10,000° roughly. And so I guess that when you combined the 9 and the 21 cm observations, this also helped prove they were thermal, or did you?
Mayer
They were at the time but yes, taking the two results separately and looking at them, it was true.
Sullivan
Yes.
Mayer
Anyway, as far as I can remember right at this same time, the line system got working. And about the first thing that happened was that they saw the absorption in front of Cas A, I don't remember what the first source was.
Sullivan
Yes, I think it was Cas. Let me ask just one more question. Was this H II region stuff published?
Mayer
Yes.
Sullivan
In ApJ?
Mayer
In two papers, the first one was in Astrophysical Journal and the second was in Nature. Now the 9 centimeter- the 21 cm was also published somewhere, I don't remember where.
Sullivan
This would be in 1953 or so?
Mayer
1954.
Sullivan
So the line observations didn't involve you. That was Hagen and...
Mayer
No, that was Hagen and McClain originally.
Sullivan
Lilley was in there somehow.
Mayer
Yes. A little later. No, Hagen and McClain actually found the absorption. And along about that time, Lilley came and then some of the remainder of the work was done by Hagen, Lilley, and McClain.
Sullivan
I see.
Mayer
But there was a lot of confusion about the absorption. To start out with- let me see if I can remember what the confusion was- in other words, it took them a long time to straighten out that this was absorption by neutral hydrogen in front of the source. That seems odd that they would have thought anything else. But I believe they had some other idea, and I can't even imagine at the moment what the other idea could be.
Sullivan
Someone has told me- I don't know if it was you or not- that they were confused. They thought the source was blocking the hydrogen or something like that.
Mayer
Yes, it was something like that. But as I say, it’s kind of hard to imagine.
Sullivan
I haven't gone back - they say if you read the first paper by Hagen and McClain you can ferret out that confusion.
Mayer
I think that's right.
Sullivan
Then [A. Edward] Lilley came along and they had the equation of radiative transfer and it's properly worked out.
Mayer
Yes, but I think there's some confusion as to who straightened it out. It may have been Lilley, I don't remember, but he was awfully confused about it, too. I can remember that for sure. He wasn't at all clear on it.
Sullivan
This is basically because they were not spectroscopists, I suppose?
Mayer
Well, Lilley was as much a radio spectroscopist as there was then. He'd just come out of Harvard.
Sullivan
I guess that's true, too.
Mayer
That was one of the two or three places in the world that was doing that sort of thing. He did his thesis on it. I don't know.
Sullivan
I'll have to ask Lilley about that.
Mayer
As I say, at the present time I can't imagine what the confusion was or why, but there was an awful lot of confusion. There was an awful lot of confusion about how to interpret the measurements and what they meant. I remember an awful lot of questions. Anyway, there was another eclipse in there, too, the 1954 one. And actually while we were on the 1954 eclipse, Haddock put a 3 cm radiometer in the 50 foot and didn't get any results at all. Again, I have never been clear why. I don't know what they were doing wrong; they were doing something wrong.
Sullivan
These eclipses were at what frequency now?
Mayer
Various frequencies. The Attu eclipse was at 8 mm, 3 cm, 10 cm, and [Grote] Reber was along at 61 cm or something like that.
Sullivan
This was using just the 10 foot dish?
Mayer
No, there were special equipments that were built. Actually for the Attu eclipse, that's not the right picture. I can show you the pictures if you're interested, but maybe you want to turn your tape off.
Sullivan
Yes, we could do it afterwards.
Mayer
All right. There were equipments that were built especially for the eclipse. And as you can see, that was one of two that was built after the Attu eclipse and was used at Khartoum and Sweden. I built that one, 100% from scratch, even the waveguide components- that was the 9 cm one. And I built the trailer mounting and everything for the 8 mm one, and Gibson and Hagen built the receiver for the 8 mm. Not for Attu but for both the Khartoum and Sweden eclipse trips, they had a big cylindrical paraboloid for the 8 mm measurement which had a fan beam, narrow in one dimension and broad in the other dimension. The narrow dimension was lined up with the path of the Moon so it could get more of a strip scan and eliminate some of the ambiguity from the sector.
Sullivan
Did this confirm the limb brightening?
Mayer
Yes, it did as much as you can confirm it from that kind of measurement. The trouble is that you don't get a singular result from a single measurement. You have to have more than one station. You have to have a station on the path of totality and one or two preferably on either side in order to eliminate the redundancies. So the solutions made on the assumptions, say, of circular symmetry did give sharp bright rings. And we tried more sophisticated models on the 9 cm at least, more oval type brightness distributions and they then gave bright edges. At least in the equatorial plane.
Sullivan
So I guess the best reference for this would be Hagen's thesis?
Mayer
No. I don't think so. Again, I don't remember dates, but I'm sure that thesis came before some of these later eclipses.
Sullivan
Oh, I see.
Mayer
Just to summarize the results of the eclipse measurements, the first one off Brazil was pretty much unsuccessful; we had the antenna on the mast of a destroyer which was bobbing in the sea and they had a hard time keeping it pointed at the Sun. The Attu eclipse [Sullivan: 1950], the equipments all worked, but a typhoon arrived the day before the eclipse and the whole day of the eclipse there was a typhoon. We took data anyway in the typhoon, but obviously it wasn't first class data.
Sullivan
During the typhoon you took data on the eclipse?
Mayer
That's right - we've got pictures showing us all wrapped, standing out there taking data.
Sullivan
Now where is this?
Mayer
We did eclipse curves, but they were ragged.
Sullivan
Right, where is Attu?
Mayer
That's the farthest out of the Aleutian Islands, about 500 miles from Siberia.
Sullivan
That must have been discouraging - to go all that way for a typhoon.
Mayer
During the Khartoum eclipse [Sullivan: 1952], the equipment worked and the weather was beautiful, but the Sun didn't cooperate. There were large active regions on both limbs and, of course, the limbs were the critical points in the eclipse curve. Of course, you could get some information on bright regions. But to get the kind of information that was being looked for on the quiet Sun, those had to be subtracted out and, of course, it's one of those things that's not possible to do really. And so, in Sweden the equipment worked and the weather was reasonably good. There was no rain or anything although there were some clouds. They didn't seem to bother the measurements very much. The Sun cooperated perfectly starting a month and a half before the eclipse date, there was absolutely no solar activity and that extended to several weeks after the eclipse. So it was probably one of the quietest periods the Sun has ever undergone. And that was excellent data and the results of that experiment were limited entirely by the ability to reduce that kind of data. You could do what you could do with it.
Sullivan
So where was this published, this eclipse data?
Mayer
Well, different places. I think the main publications are in that Jodrell Bank Symposium.
Sullivan
The 1955 one. So actually the only optical eclipse that you've seen was in Khartoum?
Mayer
The only one that was visible. Yes and I didn't go to Khartoum.
Sullivan
Oh. So you've never seen one even though...
Mayer
The only one I've seen is last year in Virginia Beach. [Sullivan: March 1970]
Sullivan
You've been to all these eclipses and this is the only one that you've seen!
Mayer
Anyway that's about the story on the eclipses.
Sullivan
So back to 21 cm line. We talked about the first. Then Lilley came along and they did some mere further work.
Mayer
That's all pretty well published, I think, and that work began with the discovery of the absorption and they did some more things with it, and it ended with the Cygnus A red shift. Which totally discouraged McClain and I guess discouraged Lilley.
Sullivan
I'm not sure I'm familiar with this.
Mayer
Well, this was an experiment that they did. You know, one of the vexing problems in radio astronomy has been to have to rely on optical red shifts. So one of the things that people have always been trying to do ever since you had lines anyway, is measure red shifts in the radio region.
Sullivan
Right.
Mayer
And one of the most intriguing objects around in the ‘50s was Cygnus A, which [Walter] Baade and [Rudolph] Minkowski claimed were colliding galaxies at that time and so forth, and they claimed that these colliding galaxies were what was then considered to be a tremendous distance, which I don't remember, but you can look it up. At that time, that was the greatest distance of anything. Now it's nothing. So it would be a great thing to find a red shifted hydrogen line, which would confirm the optical red shift and help confirm the identification and so forth, and they did an experiment in which they found a red shifted line in the proper place. But then pretty quickly some of these other people like Rod [Rodney D.] Davies tried the same experiment and got negative results. So then Lilley and McClain felt compelled to do another experiment and confirm it. The second experiment got negative results, too. So it's one of those things.
Sullivan
Did they ever publish their positive thing?
Mayer
Yes. The absorption thing.
Sullivan
Where?
Mayer
I don't know. It's in the file I think.
Sullivan
One of the astronomical journals?
Mayer
Yes, it's one of those unfortunate things where it not only was announced and published but a lot of fuss was made over it and all of these...
Sullivan
Press releases?
Mayer
Famous astronomers got all excited about it and gave it a lot of lip service, like Baade and so forth.
Sullivan
Was this an emission feature they had?
Mayer
Absorption.
Sullivan
Absorption, I see. At a few thousand kilometers per second red shift.
Mayer
I don't remember what the red shift was; it was where it was supposed to be from the object. Well, anyway, that bombed out. And nothing much after that was done on hydrogen line.
Sullivan
Did they ever publish a refutation of ...
Mayer
I don't think so.
Sullivan
Did Davies publish his?
Mayer
Yes. I think it was Davies, and maybe other people did it, too. I can’t remember.
Sullivan
Let me ask you a question on the 50 foot while I think of it. That was the largest dish used for regular astronomy when it was erected, wasn't it?
Mayer
Yes. I think it was the largest steerable paraboloid, but in any case it was certainly the largest steerable paraboloid used for short wavelengths, for many years.
Sullivan
Yes. Do you know which was the largest when it was built?
Mayer
No, I don't, but it may have been. Probably was.
Sullivan
No, no. I was saying which did it displace from being the largest in the world?
Mayer
Oh. I don't know. But during that period, there weren't really any large dishes.
Sullivan
I guess the 60 footer at Agassiz, but that wasn't usable at such short wavelengths, was it?
Mayer
No, and they didn't have it then.
Sullivan
Yes, they didn't have it until 1956.
Mayer
They had a 30 foot or something.
Sullivan
28 foot I think it was, something like that.
Mayer
The 60 foot I don't think they got until about 1955 or 1956, somewhere in there. Yes, they had this 28 foot which I think essentially [David S.] Heeschen and Lilley erected and put together, and maybe there were others, too- that group of graduate students.
Sullivan
Right. I'm a little puzzled why there weren't other astronomers trying to get to the 50 foot. It wasn't being used much. Or hadn't this tradition of outside astronomers working at NRL been set up?
Mayer
No, there certainly was no tradition of outside people working at NRL - there still isn't, really, a tradition of it.
Sullivan
Oh, I think there is.
Mayer
Well there has been for radio astronomy and a few other places.
Sullivan
I mean in radio astronomy.
Mayer
Oh, yes. In radio astronomy.
Sullivan
But I guess that didn't really begin until the Townes maser and all that. That's what started all that off. Well, before the Townes maser, I guess Venus comes before that, right?
Mayer
Yes, but the other thing I wanted to mention was that during all this period, too, a lot of work was devoted to radiometer development and technique development. And I think personally, that is what really paid off in the end. I mean for a number of years, nothing much came of it, but then that's what made it possible to do the measurements that were done later on the 50 foot.
Sullivan
Yes.
Mayer
For example, development of such things as Ferrite switches and methods for using gas tubes for calibration, absolute calibration of gas tubes - that was all done here.
Sullivan
Well, now, in fact you personally were responsible, you were the one who worked on the Ferrite switch, were you not?
Mayer
Yes, and some of the gas tube work and Sees and Corbett and some of the gas tube work and particularly the absolute calibrations. They, in fact, did calibrations for the Bureau of Standards as I remember.
Sullivan
And what was the switch a new concept or was this something you adapted from some other...
Mayer
It was adapted; it was a new concept, but not new here. And I can't remember for sure where the concept first came into being, but I think it was in Holland that the Ferrite materials were developed, and again, I'm not absolutely sure, but I'm fairly sure that the concept of the isolator and circulator using the Ferrite components in wave guide was initially proposed and demonstrated by a guy named Hogan at Bell Labs. He published a paper in Bell System Technical Journal describing the isolator and circulator, which I saw and thought it was immediately obvious that this should be used in radiometers.
Sullivan
I see.
Mayer
As you see, principally for this reason, that up until then, the toughest problem was calibration. The schemes for calibration a were using hot lobes and that sort of thing, which the usual procedure was to unbolt the feed and bolt on a hot lobe, well not only did that take a long time and introduce errors but there was a big systematic error in this whole procedure because the impedance of the source was not the same as the impedance of the horn or when you had to put two sources, like a hot lobe and an ambient lobe to get the calibration spread...
Sullivan
30 September ’71 at NRL. Ok, we're talking about Ferrite switches.
Mayer
But even if you really broke your back to match everything, standing wave ratio of 1.02, or something like that, over the band of the receiver, it still is virtually impossible to get away from errors of 5° or 10° from your source.
Sullivan
Yes.
Mayer
And of course, the isolator, but even better, the circulator knocked that error way down. By a factor of ten or a hundred.
Sullivan
About what time was this that you saw this article and started working on it?
Mayer
About 1950, ’52, somewhere in there.
Sullivan
Oh, that early?
Mayer
Yes. In fact, the applicator, well then the obvious thing to do with the circulator is to instead of using a fixed magnet to switch it, and use it to replace the ferrite switch, which would give both the advantage of the impedance isolation, getting rid of this calibration error, but would also get rid of the dipper disk - almost always been used up until that time.
Sullivan
Right.
Mayer
Certainly it had always been used at short wavelengths or some artificial replacement for it. But that had all sorts of advantages, you could switch between two antennas or you could switch between anything you wanted to. That led to the development of this 3 cm radiometer which was used on the 50 foot in ‘56 and that radiometer was actually in development for two or three years but was held up by these eclipses and stuff. The ferrite switching stuff was actually done, I think, by 1952 or 1953 and just sat there for two or three years. Anyway, in 1956 we- this was I guess Haddock left somewhere in 1955 or something like that- and well, again, for various reasons, with Haddock leaving and with Hagen finally being saturated with eclipses, this made it possible for me to work full time on this radiometer and get it in the 50 foot. And immediately in putting that radiometer in, the first thing we did was look at Venus, and we asked for a month's time, because we wanted to look for phase effect.
Sullivan
Now...
Mayer
In other words we thought the sunlit side of Venus should be hotter than the dark side, and we wanted to see if we could measure the surface temperature of Venus. And also to see if the sunlit side was hotter than the dark side. The sort of thing you did on the Moon, you see, previously.
Sullivan
Right, but Venus had never been observed at radio wavelengths?
Mayer
No.
Sullivan
So this was just your idea that it should be observable?
Mayer
Yes, based on the infrared temperature of 300°.
Sullivan
And with, I guess, reasonably low noise at that time, 3 cm receiver. I'm just trying to get a feel; I guess the main thing was the large dish usable at short wavelengths that enabled you to do it.
Mayer
It worked out that the antenna temperature was of the order of 2° or 3° and just to do something like that and it would be observable. As I say, we asked for, I guess we actually asked for two or three months time, but they gave us one month, so we started out about a month before inferior conjunction, our time was up right at inferior conjunction. And the first day, we did pick up Venus, and it was not only farther from conjunction, but also farther from the Earth. It was- I've forgotten now, but probably 1° or less on antenna temperature. So right away it was apparent that if it was thermal radiation from Venus It wasn't 300°, it was 600°. The very first day that was apparent.
Sullivan
Really, you had no doubt about the alleged signal, shall we say, that time, you mean?
Mayer
We didn't have any real doubt, of course we had all sorts of doubts because everybody told us and all the books told us that this was impossible. And so we had all sorts of doubts. We had no doubts about our equipment because that equipment was very thoroughly designed, Every individual component had been thoroughly tested. Overall system was thoroughly tested the calibrations very well checked, the thermal sources, we felt very assured about what we were measuring, but we couldn't feel very sure about Venus being at 600° because all the real smart astronomers said this couldn't be so.
Sullivan
Yes.
Mayer
And so, well, in fact, [Wilt?] had worked out that there would be a greenhouse effect assuming there was carbon dioxide as they thought there was, but he set an absolute upper limit of 400° for the possible temperature. So even with that assist from [Wilt?] on the greenhouse, it was still impossible. Anyway, we continued to measure Venus up to inferior conjunction, and we saw this downtrend in the brightness temperature as it got toward inferior conjunction. And of course, as Venus got closer, the antenna temperature went up like it was supposed to and so forth. About that time, we got tossed off of the dish. And we couldn't follow it through on the other side of inferior conjunction.
Sullivan
But you said the brightness temperature was falling?
Mayer
The antenna temperature was going up, as it should.
Sullivan
Right.
Mayer
But of course, not as fast as it should if the brightness temperature was falling.
Sullivan
Right.
Mayer
Anyway, we couldn't do anymore, we got kicked out. Then we begged and pleaded that we be allowed to put the 9 cm radiometer on to check to see if another thermal spectrum. So Hagen gave us two days on a weekend about a month later. So we worked all night in a thunderstorm to mount that huge radiometer which is in a box about this big and weighed a ton up on the back of the 50 foot dish, run 10 cm waveguide this big all the way up to the focus. The next day measured Venus. That measurement wasn't awfully good because it was still too close to the Sun at that wavelength and we had some side lobe troubles. But he gave us one day a month later to try it again, and we went through the whole procedure again. And this time we got some fairly marginal measurement at 9 cm, which could have been improved, of course, with a few days time, but...
Sullivan
Yes.
Mayer
But it did indicate a thermal spectrum.
Sullivan
Was the dish being used 100% of the time now or was this, once again, that he just wasn't willing to give you time?
Mayer
Oh yes, it was being used - mainly for the hydrogen line. I think that may have been about the time that Lilley and Barrett were looking for OH, and they were screaming their heads off that we shouldn't waste time on the valuable antenna looking at Venus. In fact, we had a terrible time getting on the antenna at all for that reason.
Sullivan
Now do you know if that experiment came out - they just didn't have enough sensitivity to find OH?
Mayer
I never understood why they didn't find it. When asked, their answer was that they didn't know the frequency well enough, but I've never understood that answer. Maybe that's right, but it seems to me that, well…
Sullivan
Let's see now, the Venus stuff was published most certainly, and that was in ApJ?
Mayer
Yes.
Sullivan
Now what about the phase effect?
Mayer
That came later, but before that another thing that we had in mind to do at 3 cm was to try to detect polarization on the Crab Nebula. And we wanted to have some kind of comparison source anyway, for the Venus measurements. So we looked at the Crab Nebula and Venus all day long every day during this two month period - all the way across the sky. Of course, this inferior conjunction was in June- 23rd I think. So Venus and Taurus were practically in the same part of the sky - all through the whole experiment. But anyway, we looked at both Venus and the Crab Nebula all day excepting right before [?] one to the other. So we had this data on the Crab Nebula, linearly polarized feed all day long, [paralaxic?] angle at that declination rotated like 120°, I think it was. And after the first month, we rotated the whole radiometer 90° so we could fill out the other part of the curve and verify if it really was a polarization effect or whether it was some other kind of systematic effect during the day. And those curves, in fact, did show that for one, I can't remember which one now, but I guess horizontal polarization during the day that the thing looked like this. The vertical polarization went down like this. As it should for polarization.
Sullivan
So what percentage was it approximately?
Mayer
Hmm, yes I remember, 8%, I think.
Sullivan
And was this the first radio astronomical polarization detected? And I guess it was [Iosef Samuelovich] Shklovskii that first proposed synchrotron radiation. No?
Mayer
No.
Sullivan
Had that been proposed -did you have any idea of where this polarization was coming from?
Mayer
Oh sure. Oh sure. That was why we looked for it.
Sullivan
Then who was it then?
Mayer
Well, synchrotron radiation as an explanation for celestial radio sources was first proposed by [Karl Otto] Kiepenheuer for the galactic radiation and by [N.] Herlofson and [Hannes] Alfvén for radio sources. Discrete sources.
Sullivan
Can you tell me approximately where and when these proposals were made?
Mayer
I can give you the references. In fact if you look at our polarization paper, they’re in there.
Sullivan
Okay, fine.
Mayer
And this was in about 1950.
Sullivan
And they were saying that this was for Cygnus A also for the extragalactic?
Mayer
I don't remember whether they specified particular sources; they were just suggesting this as a possible mechanism for explaining this radiation, which by this time everybody agreed couldn't be thermal. So there were these two independent suggestions of synchrotron radiation. And somewhere along in that same period of time but I think even the Russians admit later a whole bunch of Russians proposed things like this, notably I guess [Vitaly L.] Ginzburg and maybe Pikel’ner and a bunch of guys proposed synchrotron radiation, and maybe independently, maybe they didn't even know about this outside of Russia, I don't know. What Shklovskii did as far as I know, anyway, he's not the first guy that proposed synchrotron radiation for radio sources at all. Not even in Russia. By my understanding, what he did was to propose that not only the radio radiation from the Crab Nebula was synchrotron radiation but also the optical, and that was done about 1953, that proposal.
Sullivan
I see.
Mayer
And as a follow-up on that proposal of his, a couple of Russians looked for optical polarization and found it.
Sullivan
And found it?
Mayer
Yes.
Sullivan
Before your radio polarization?
Mayer
Yes.
Sullivan
So you did have that to go on, at least?
Mayer
Yes.
Sullivan
So that optical polarization was pretty strong proof, well, not proof, but weight on the side of synchrotron in the radio...
Mayer
On the optical, yes.
Sullivan
The radio, just about clinched it for radio.
Mayer
Yes. And that they were, in fact, the same process.
Sullivan
Right.
Mayer
And also, I guess independently, [Jan Hendrik] Oort claims independently, Oort and [?] looked for optical polarization and I think they didn't know about the Russian results, which in fact though had already been gotten. And they found polarization, actually made a polarization map, a crude one, optically. And then according to Oort, Baade was over there and he showed Baade and this and Baade went back and took these famous photographs with the 200 inch, which show the different sheets of polarization, which showed the polarization very definitely and then [Lodewijk] Woltjer of course took Baade's photographs and analyzed them and got these very high resolution polarization pictures by analyzing Baade's photographs.
Sullivan
Now I suppose this polarization measurement, maybe the Venus, too, is an example of the earlier equipment work that paid off in the late ‘50s.
Mayer
That's right. So anyway, as a result of that what we thought was a definite detection of polarization, but we wanted to confirm it better, so then we built a rotating feed radiometer, and I don't remember when but I guess the next year, and we confirmed it with the rotating teed and got better data and stuff and published it. And then somewhere along in those same years, I don't remember where, we also looked at Mars and Jupiter and we, of course, looked in this period, we looked at the strong radio sources and got what appears to be good data and flux as anybody ever had, but we didn't ever present it that way or publish it that way.
Sullivan
In any of these projects you haven't really mention other people as competitors or anything; was NRL just pretty much on its own or did you feel pressure from anyone else?
Mayer
There weren't any competitors at these wavelengths because we had the only 50 foot dish.
Sullivan
That must have been a nice position to be in.
Mayer
Yes. And your other question about weren't astronomers clamoring to come to NRL and look at stuff, I don't think they were although even if they were, I might not have known about it, because they probably would have come to Hagen.
Sullivan
Yeah.
Mayer
But I don't think in general that astronomers were clamoring to do anything with any radio astronomy stuff; they were still taking a strictly hands-off attitude.
Sullivan
Yeah, yeah.
Mayer
And looking down their noses.
Sullivan
And there were very few people that you could really call radio astronomers at that time.
Mayer
That's right. In fact, the Venus measurement, the only real astronomer who paid much attention to it and certainly the only one who gave us any support, was [Gerard] Kuiper. And guys like [Donald H.] Menzel just poo-pooed it and said they didn't know what we were doing wrong, but we must be doing something wrong. And did we really know what we were measuring, did we really know what we were doing- all that kind of nonsense, you know. But Kuiper was not only right away receptive to believing that people other than astronomers could do things, too, but he also was not so blind to the possibility that maybe they didn't know all about Venus and maybe it could be 600°. And he somewhere along in there started Carl Sagan working on this, who was his graduate student in Chicago.
Sullivan
I see.
Mayer
And Sagan was trying to explain the high temperature by greenhouse effect basically.
Sullivan
In general, was there trouble in publishing radio astronomy papers in things like the Astrophysical Journal in the early 1950s?
Mayer
Not as far as I know.
Sullivan
So they were accepting to that extent?
Mayer
My impression would be that there may have been some trouble but we certainly never encountered any real trouble. Maybe radio astronomers thought there would be trouble and didn't really try sometimes when they should have.
Sullivan
Yes. But there's still, you've hinted a lack of acceptance by most of the optical astronomers.
Mayer
Well, a lack of enthusiasm and acceptance. And there's always been a great reluctance for astronomers to accept NRL on any perspective.
Sullivan
Why do you think that is?
Mayer
It's partly snobbery and partly that universities don't like competition from government installations.
Sullivan
That's interesting. Do you think that applies for the Naval Observatory also?
Mayer
Yes. As far as research is concerned, they're perfectly happy to have them do ephemerides so they can use them. I think so. I don't have any information on that, of course, but I think so. I think it's still true today.
Sullivan
Well they certainly look upon an academic post as being a more favorable or exalted position or what have you than a civil service post. There's no doubt there's snobbery to that extent.
Mayer
Yes. I think that's always been the feeling - only second grade people would work with government, that sort of thing. If you're any good, you'd be at Harvard.
Sullivan
Yes. Well, that covers up to the 84 foot. Did you work on the 84 foot at all?
Mayer
No, or very little. Worked some on it and we tried to make some polarization measurements, well, we did make some polarization measurements at 10 cm. Well, that leads into all this follow-up work on the planets and the polarization. I mean we looked for even in the first measurements, we obviously looked for polarization on the other strong radio sources not just the Crab.
Sullivan
Yes.
Mayer
And... that may not be entirely true. I don't think we did look at Cygnus until 1961. I don't remember why that was. But anyway, all these things led to other things. For example, we couldn't understand why we didn't see polarization in Cas A; you obviously should. And there were only two possibilities: one was that the magnetic field- well, three I guess, now synchrotron radiation could be a possibility- the magnetic field was entirely disordered or it was symmetrical. And that was the basis for the experiments a few years ago with the 140 foot, map of polarization of Cas A.
Sullivan
I see.
Mayer
To find out - was it disordered or was it ordered? It turned out to be ordered. And so on.
Sullivan
At what point did the Radio Astronomy Branch become such devoted to radio astronomy almost?
Mayer
Oh yeah, well, there was something like 1954, ’53 or ‘54, it became the Radio Astronomy Branch and it still wasn't entirely devoted to radio astronomy, but it was called then Radio Astronomy Branch. And at about that time, Hagen became Division Superintendent. And what was the Division called then? I don't remember.
Sullivan
A and A?
Mayer
Well, I think he renamed it A and A [Sullivan: Atmosphere and Astrophysics]. I don't remember what it was called before.
Sullivan
Who became the branch head when Hagen moved up?
Mayer
A guy named [Sullivan: Warren] Ferris who had been Assistant Branch Head - he's the guy that Hagen got from RCA, he was a middle-aged fellow and I was never quite clear why he got in or why he came here - he had no interest in anything that was being done. He's a tube man. And he certainly had no interest in radio astronomy. But he had been Assistant Branch Read for a long time and also obviously, again, you don't have to repeat this, but obviously Hagen had in mind that as Division Head, he was still going to run this branch, because he was still interested in radio astronomy.
Sullivan
Yes.
Mayer
But anyway, Hagen only remembered Division Head for something like a head, and then he took on this post as head of Vanguard at which time Newell became Division Head. And Newell was Division Head then for two or three years until he left with the crowd that went to NASA.
Sullivan
And that's when Friedman took over? And who followed Ferris as Branch Head?
Mayer
Well, Ferris, I know, only remained as Branch Head for a year or two, he found the situation untenable. He went to University of South Carolina and McClain became Branch Head and that was in about 1956 or somewhere around there.
Sullivan
Had McClain acquired an interest in radio astronomy?
Mayer
Oh yes. I guess I skipped that - I said...
Sullivan
You said he started off with zero.
Mayer
When I said he was not the least interested, in fact he didn't want to do this at all - he was working in the Doppler navigation system, which he was interested in. But when they pointed the thing at these radio sources, he got mildly interested, I think. But then when they found this hydrogen line absorption thing, he became very interested. I converted him. But anyway, to answer your question, for a few years, along in that period, probably still only about half the branch was working on radio astronomy. It would have been at least until these people left or came or something - it would have been a group, in the ‘55, say, ‘56 era, it would have been Hagen and Haddock and McClain and Sloanaker and McCullough and Gibson and I've forgotten some, but that's basically it. And then a few other guys like Corbett.
Sullivan
There's another thing that we haven't mentioned is the maser collaboration.
Mayer
I haven't gotten that far yet.
Sullivan
We're still...
Mayer
We're about there. Anyway, what you should also have somewhere in your records is that shortly after the detection of Venus, Gibson and McEwan, who was a technician at that time here- Scotty, maybe you've even heard about him, I don't know. They measured Venus at 9 mm and they found the lower 400° temperature at 9 mm. So actually, if you're wanting to accept the very marginal 10 cm result, the spectrum of Venus essentially as it’s known today was found here in about 1956, ‘57.
Sullivan
Was that published - the 9 mm?
Mayer
Yes. That in the Paris Symposium if I remember correctly. Then that was extended further by Grant, I think, who measured Venus at 4 mm using the 10 foot and got still lower temperature, 300° or something. Anyway, the spectrum of Venus was very well delineated at NRL. And of course, about 1957 or 1958, NRAO got their first 85 foot and Drake right away went on Venus at 10 cm.
Sullivan
Yes, that was 1958. That was the first time you had any competition. So is the next step…
Mayer
Well the Townes maser, that was a collaboration or set up, I guess, initially in talks between McClain and Townes. Townes had graduate students building masers and he wanted to apply them to radio astronomy and the 50 foot dish was the best place to do it. So he contacted McClain and we worked with him first of all on the 3 cm measure on the 50 foot and next I guess it was the 21 cm measure that I know Penzias built and that was on the 84 foot. And then I guess next was Bill Rose who built a 10 cm maser and that was used on the 84 foot. I don't think I've forgotten any.
Sullivan
Was there anything particularly troublesome in adapting these things as radiometers?
Mayer
No. Not really, I mean there were troubles, of course, but nothing basic.
Sullivan
Nothing so they had to operate upside down or things like that?
Mayer
Operate what?
Sullivan
Upside down and out in the elements.
Mayer
Oh, no. [?] problem. Of course, an alt-azimuth mount is not such a bad problem, but just mounted at 45° so you could cope with the zenith down to the horizon.
Sullivan
Let's see. The other thing that comes to my mind that you've been involved in is you know, very recent, namely the Townes collaboration with the water and ammonia lines.
Mayer
Yes.
Sullivan
Of course I know some of that myself, but I was just wondering if you would talk about just how that collaboration was set up. The way I know is simply that Townes was looking for a bigger telescope, and since he'd worked with NRL before, it was natural for him to give you a call.
Mayer
Yes. Well, let's see, as best I can remember it, he called and said they'd detected ammonia, and that he thought it would be really good to look at it with higher resolution and so forth. So we were planning to try to get something together and do this and a couple of weeks later he called and said they'd found this water - which looked a lot more interesting...