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Oral History Transcript — Dr. W. John Cocke

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Interview with Dr. W. John Cocke
By Spencer Weart and Joan Warnow Blewett
Telephone interview
February 19, 1975

open tab View abstract

Dr. W. John Cocke; February 19, 1975

ABSTRACT: Deals with the events leading up to and the discovery of the Crab Nebula Pulsar. Comments on his education at Cornell University and switch to astrophysics. Teams up with Michael Disney at Steward Observatory for their first observation on a 36-inch telescope. Discovery of the Vela Supernova remnant pulsar convinces them to concentrate on the Crab Nebula rather than white dwarfs. Discussion of preparations, of observations, and of the discovery. Reaction to the discovery, effect on future work. Also mentioned are: Robert McAllister, Don Taylor, and Dr. Weyman.

Transcript

Cocke:

Ok, Iíve got a seven inch reel on here. The record meter is still as always within the green range. So I think we're in pretty good shape.

Warnow:

I donít care too much about our recording except to have a record of the whole thing intact, you know.

Cocke:

Right. Will do. Will do. Ok.

Weart:

Because the transcriber will go crazy trying to figure what the questions were otherwise.

Cocke:

Right, sure. Yes, no doubt.

Warnow:

Ok. We settled that much of it and I want you to know that I did go back and check our version of the moment of discovery tape you had and it does begin with observation 13.

Cocke:

Right, you did, huh? Ok, thatís where it should -- well, yes. Actually, I have, I discovered a transcript of that recording which was done by the BBC.

Warnow:

Right. I did see it in that Crab Nebular film. Right.

Cocke:

Yes, right. Theyíve written the whole thing down for us. I can send you guys a copy of that, if you want it.

Warnow:

I certainly would appreciate it because we tried to have it transcribed here and itís such a frightening thing to do.

Cocke:

You have, right. Ok, why donít I do that? Iíll send you a xerox copy. Unfortunately, the copy Iíve got is already a xerox copy. So --

Warnow:

Thatís good enough. The other thing you were going to do is take a look at some of your note book observations for that evening and send a clear xerox from that, if you can or if there is a way of taking a photograph of certain pages that would be very good too.

Cocke:

Ok. Yes, I think a xerox would probably be all right there.

Warnow:

Ok.

Weart:

Ok, great because that would be very nice to include in the package too, of course.

Cocke:

Yeah, Ok, sure. Thatís a thought.

Warnow:

I havenít heard from Disney yet but I havenít given up because itís too soon.

Cocke:

Oh, sure. Oh, heíll love it, Iím sure heíll be very cooperative.

Warnow:

Ok, hope so. Spencer Weart is the astrophysicist in the group here and I know I have certain things here I know I want included but I think Spencer will be asking more of the technical questions, ok?

Cocke:

Alright, fine. Fine. Uh huh.

Weart:

Why donít I just get started? You know I used to be in solar physics actually and 1 can remember it very well -- letís see, I think I was in Colorado at the time as a matter of fact and I remember the rumor going around about these young guys who had scooped everybody around with the 36 inch telescope and were uneasy about it and so on.

Cocke:

Yeah, right, that was certainly the case.

Weart:

I am certain you must have had some reaction yourself on that?

Cocke:

How do you mean?

Weart:

I donít know, did people kid you about trying to do what other people had tried to do with a large telescope and had failed?

Cocke:

Uh huh. Well, the problem really was that this was the first time that weíd ever used a large telescope, a largish telescope. This was only a 36 inch. And the operation that we were doing itself was quite complicated electronically, and so, Disney and I were virtually unfamiliar with telescopes and with electronics.

Weart:

You know, I know very little about your background. You were an astronomy graduate student at the time? How did you come to get interested in astronomy?

Cocke:

Well, physics -- not at the time. I had gotten my degree from Cornell in Ď64, and Iíd studied, Iíd majored in theoretical physics with a minor in astrophysics, so I did know a fair amount of astrophysics, but that wasnít really yet my bread and butter. Iíd always been interested in it. I remember, when I was a young kid, my great-aunt had given me a book on astronomy, and that interest had carried through until, you know, over the years, until finally, having gotten my degree in physics, I thought: well, Iíll just go ahead and see what I can do in astronomy itself. So I switched over.

Weart:

You switched careers?

Cocke:

Well, itís not as drastic as it sounds, because really, astronomy today is in large part applied physics, so if your physics isnít in good shape, then you can do astronomy.

Weart:

So what did you do? You just applied for a job in Astronomy? You were about Post-Doctoral type at that time?

Cocke:

Yeah. What I had done was to -- I had been working in gravitation theory, Einsteinís theory, and to go from there into astrophysics and into astronomy, is itself not a very big step, because people had at that time been trying to connect general relativity with astrophysics, and particularly with the theory of quasi-stellar objects.

Weart:

So you were already interested in small mass objects from a theoretical stand point?

Cocke:

Right, yes. Yes.

Weart:

Was this how you happen to get interested in pulsars?

Cocke:

Well, everyone was interested in them, I suppose, when they were discovered. It immediately became a very, very popular thing to try and work on.

Weart:

Pulsars?

Cocke:

Yeah, right.

Warnow:

How did you get out to California?

Cocke:

California, Well yes. Stewartís in Arizona.

Warnow:

I knew that, I somehow had the impression of all of you coming from Cal Tech or something like that. How did you all get together?

Cocke:

We were all -- well, we were brought together, more or less, by the observatory. Don Taylor was already here, and Disney had come over from London, I think, University College, with the intent of working on, letís see, star formation, as I remember it -- star formation and generally galactic dynamics, I believe. Yes, I met both him and Don Taylor, Stewart --

Weart:

How did you get to know Disney?

Cocke:

Oh, it was a fairly easy thing to do. Disneyís a very outgoing type, and as it turned out, we both arrived in Tucson at about the same time, in the middle of August, in Ď68, I guess that was, and we were both staying at the same motel, as it happened, before -- you know, while we were looking for a more permanent place to live. And so as I recall, my wife and I met him and his wife at the swimming pool, at the motel, and started talking about what we were doing in Tucson, and it turned out that we were both astronomers and were both going to be at Stewart Observatory. So we met at a motel swimming pool, really, rather than at the observatory.

Weart:

He was more of direct line astronomer?

Cocke:

Well, he was still a theoretician himself, being interested in the theory of star formation. He, as I said, himself had had no experience at all, at working with the telescope.

Weart:

And neither had you, of course?

Cocke:

Right, I hadnít either.

Warnow:

So he was a theoretical physicist and you were a theoretical physicist and somehow Stewart Observatory wanted you both?

Cocke:

Right, yes. Yes.

Weart:

So you were a theorist so to speak?

Cocke:

Yes, as a theorist, but already as an astrophysicist. I had -- afterÖ

Weart:

Did you have any trouble with that? Did they just accept you when you said you wanted to do Astrophysics?

Cocke:

Well, Iíd already done some, you see, because going from gravitation theory into astrophysics had already been done by me a couple of years before then.

Weart:

I see and they just accepted that as your qualifications?

Cocke:

Right. Sure. Sure. Yes.

Weart:

How did you get the job, by the way? Iím always curious about these things.

Cocke:

Oh well, these things, jobs like this, job openings are passed around, or they used to be passed around more by word of mouth, from professor to professor, right, someone the person whoís trying to find applicants for the job opening will call up friends of his in various quarters, in various corners of the earth, and ask if they know of anyone who would be interested or whoíd be good and be qualified for the particular opening that they have. Now, --

Warnow:

I wanted to ask you a question? First of all I want us all to remember that we are not trying to cut each other off, we should literally leave 10 seconds of time between each questions and answer. I remember the editor; the tape editor suggested that so that he can make excerpts more easily.

Weart:

I am sorry Joan.

Warnow:

The other thing is who did you do your Ph.D. thesis with at Cornell?

Cocke:

I did my thesis with Phil Morrison. Yes, right.

Weart:

He is quite a fellow, isnít he?

Cocke:

Oh, he is, yeah, Phil is really an extraordinarily -- well, how shall I say? Articulate and very, very learned and a very broad person.

Weart:

What were your relations with him like?

Cocke:

Well, he -- it was a little difficult at the time, I remember. He was in the process of moving to MIT, and so was -- so trying to do a thesis with him was, oh, well, it was a bit of a long distance thing. I was actually involved in writing my thesis at the time when he had actually completed the move to MIT. This was in 1964, spring.

Weart:

By the way you didnít have anything to do with the Outing Club by any chance?

Cocke:

The Cornell Outing Club? Oh, you were? Well, Iíll be darned, Spence. Gee. Well, Spencer, I didnít really-- no, I didnít, in fact.

Weart:

The graduate student just didnít have the time.

Cocke:

Well, yeah, thatís often the case. I found, though, that as a graduate student, I had more spare time than most of my undergraduate friends did. Yeah. The undergraduates there had a really hard time of it, as I remember. Itís a very tough school for undergraduates.

Weart:

Gee. Did you think so?

Cocke:

Yes.

Weart:

Well, we really ought to get back to the pulsar.

Cocke:

Oh yes.

Warnow:

I sort of wondered if you kept in contact with Morrison afterwards. While you were working on this while you were at Stewart, before the actual night of discovery.

Cocke:

Ah, with the pulsar thing. No. This is the sort of thing that -- well, letís see, I had actually lost track of Phil, or lost contact with him, I should say, over the years since getting my degree. And I donít recall having any conversations with him about the proposed observations.

Weart:

Letís get back then, you were, you met Dr. Disney there and how did your talk turn to doing optical searches for pulsar? Did it start out that way or did it start out with well we should do some observations?

Cocke:

It started out from both directions, as I remember. We had both thought that it would be a good thing to get experience at the telescope, just as a thing in itself. And we had also thought from time to time about doing something really relative to pulsars. And what we had proposed trying was, to search for optical pulsations from white dwarfs. At the time, white dwarfs were still very, very good candidates for being what pulsars were. And we had thought that, well, since optical pulsations had not yet been discovered from non-radio pulsars, we had thought that perhaps there were white dwarfs that didnít have any radio pulsations, but that did have optical pulsations. So what we were going to do. What we proposed to do first was to search known white dwarfs for optical pulsations.

Weart:

Were you serious about going into observation work or did you just think that this is something that you might try your hand out a little bit?

Cocke:

Well, we werenít sure. This was a tentative first step, and itís hard to know when youíre going into something like that whether you really want to stick with it.

Weart:

I see. You didnít know whether you wanted to become an observational type or not?

Cocke:

Right. Right. Right.

Weart:

Have you decided yet by the way? What you doing now, are you doing observational or theoretical?

Cocke:

No. Iím doing mostly theoretical work at the moment.

Weart:

But a little observation too?

Cocke:

Yeah, every now and then I -- well, I suppose the last observational work that I did was still with the pulsar. Last, about a year and a half ago, I guess, we did some work to establish differences -- well, differences in the shape of the crab pulsar light curve, with respect to color. That is, the pulse seen in blue light does turn out to be slightly different from the pulse seen in red light. Ok.

Weart:

Right, I remember that in fact. So then you decided to look for white dwarfs and you applied for pulsar at Tucson?

Cocke:

Right, we did.

Warnow:

Is this all, by the pool by the way? I am getting a glimpse of you meeting at the pool and having this whole conversation about setting up a project right away, is that wrong?

Cocke:

No, no, it didnít happen that way. As it turned out, this -- we started talking about this, as I remember, probably, oh, in I suppose September or early October, something like that.

Warnow:

Uh Huh.

Cocke:

Well, as it turned out, people had already done observations of this type on white dwarfs. After digging around a bit in the literature, we discovered that, and so, --

Weart:

Only you mentioned in this article that you put out, you know this thing it mentioned that you heard about this thing from R. J. Weyman?

Cocke:

Weyman, yeah, uh huh. Right. Weyman is now chairman of our department here. At the time, we were talking with Weyman simply because heís a very good general all around astronomer and astrophysicist. Heís been with Stewart ever since Iíve been here. So, we discovered from Weyman and from digging around in the literature that quite a bit of work had been done already on this sort of thing, with negative results. So we were a bit discouraged. Then it turned out that a pulsar was discovered, not the Crab Pulsar yet, but one in the middle of the Vela Supernova remnant, which had a period much, much shorter than any of the other known pulsars, and it pretty well convinced people, and convinced us too, that pulsars were indeed not white dwarfs, but rather neutron stars. And then finally, I think maybe a month later the discovery of the radio pulses from -- of the Crab Nebula pulsar, from the general direction of the Crab Nebula, was announced.

Weart:

Did you just read about that in the literature or did you just hear about that?

Cocke:

Well, I remember -- letís see where did we hear about this? I suppose it came over on these international astronomical union telegram things, you know, these circulars that the IAU sends out? They come out, you know, on a rather irregular basis, average once every couple of weeks or so, announcing discoveries of various sorts. And itís very likely that this discovery by [???] and [???] at the, oh, National Radio Astronomy Observatory in Greenback, West Virginia, was announced.

Weart:

I see by this time you were well into astronomy so that you were watching the bulletin board, however, for these things.

Cocke:

Oh, right, yes. The discovery of the Vela pulsar generated quite a bit of excitement, and then, following that, the discovery of the Crab Nebula pulsar really raised things to quite a pitch.

Weart:

There was a lot of talk at Stewart about it?

Cocke:

Yeah, there was, uh huh, sure. Well, everywhere, all -- I suppose most of the astronomers all over the world were talking about it at one time or another.

Weart:

How did this affect you there at Stewart? How did you know that there was this kind of atmosphere? Where did you see it?

Cocke:

Well, you could -- I can only imagine that. Oh, you mean, how did we feel about that sort of atmosphere directly at Stewart? Yes, well people were talking about it, wondering what in the world these things were, and why, and everyone was being rather astounded at the apparent connection with the Crab Nebula. Well, this was what really pinned it down for us, because what we then did was, we went to do a rather more thorough study of the Crab Nebula ourselves, to see if we could pinpoint where, within the Nebula, the pulsar might be. And we found that a star in the center of the Crab Nebula, which had been known as Bottaís Star, was indeed a very peculiar object in its own right. It had a continuous spectrum in the optical, and no absorption or emission lines of any sort, and had been presumed by Botta and by McKowsky to be the core left over from the supernova explosion that produced the Crab Nebula. So we felt, well, thatís a likely place to start. So, the radio telescopes at that time didnít tell us, couldnít tell us, really where this thing was, except that it was in the general direction of the Crab Nebula, because the resolution at that point, the radio resolution was very, very poor. So we had to go to the Nebula itself, and ask what peculiar -- ok, Joan.

Warnow:

I am a little confused so I am going to break in. The radio telescope couldnít tell you where the pulsar NP0532 was but you could locate Bottaís star? Ok. Letís keep that straight.

Cocke:

Right. Right, sure. Yeah. Right, yeah. So what we did was -- we said, well, why donít we make some observations of Bottaís star itself, to see whether or not it might be pulsing at the same period that the radio pulsar had been discovered to pulse at.

Weart:

And we, this is still you and Disney? And where were you when you talked this over?

Cocke:

Yes, this was still me and Disney. Yes.

Weart:

Did you have adjoining offices or did you or were you still in the same motel or what?

Cocke:

We were -- this was at Stewart, now. Letís see, Disneyís office was, as I remember, right next to mine, in fact, so we had ample opportunity to get together there.

Warnow:

Lets have, a time fix on this? When did you hear about the discovery by Bell and Hughish of that strong pulse flux? I am sorry, not of the flux but about that point radio source?

Cocke:

Well, yes. Now, the point radio source in the Crab Nebula -- thatís a different object. Well, actually, itís the same object. See --

Warnow:

I know but in the little write up you made Maglishís Journal

Weart:

Oh that is already known Joan -- that was back in 1967.

Warnow:

Yeah, I would like to know how that fit in though to this whole story on the tape.

Cocke:

Well, yes, at the time it was just another peculiar object, associated with the Crab Nebula. And as it turned out, that so-called peculiar low frequency radio source, as itís known as, is really the low frequency pulses from the Crab pulsar that had been smeared out and scattered by interstellar scattering.

Warnow:

Uh huh?

Cocke:

Ok -- because as you look at the Crab Pulsar at lower and lower frequencies, the pulses get more and more washed out and smeared, and finally, you reach a point where , I would say, below 100 megahertz, where you can no longer really see pulses at all.

Weart:

I see so this was one more thing that you turned up in your literature search -- another weird thing in the crab?

Cocke:

Right. Yes. Yes. Now Ė

Warnow:

And you want to make a connection between all of these points?

Cocke:

Yeah, there are all sorts of things floating back and forth here; the thing is this so-called low frequency radio source hadnít been pinpointed by the radio astronomers yet, as to its location. They had a fairly large aero box associated with it, which was much, much smaller at that time than the aero box associated with the pulsar, but still it covered a sizable part of the Crab Nebula.

Weart:

Including Bottaís star?

Cocke:

Yes, right, it was centered on Bottaís Star. So this said, well, this made us think that this peculiar radio source was also associated with the pulsar, and hopefully with Bottaís Star. Ok.

Weart:

Ok. Now how did D. J. Taylor get brought into this?

Cocke:

Well, in our conversations with Weyman, he suggested, as I remember, that we get together with Taylor, because Don Taylor was by far the most adept person at the observatory, with instrumentation, and with electronics. And --

Weart:

I see, Weyman as sort of playing the role of your guide here, is he a little older than you?

Cocke:

Oh, yes. Yes. He was at that time sort of the head theoretical force in the observatory.

Weart:

I see so he was the sort of person you went to for advice about anything that happens to be going on.

Cocke:

Right, yes. Yes. Sure. So, anyway, he brought Don Taylor and Mike Disney and me together. And we talked with Taylor, and as it turned out, some of the instrumentation that Taylor had developed was very easy to convert over into the sort of configuration that we used to discover the pulsar. So, getting together with Don Taylor was a -- was a very fortunate and natural thing to do.

Weart:

What did he develop?

Cocke:

He was working to develop an area scanner, for, letís see -- they had a number of projects going. I think one of the projects involved doing area scans of the planet Venus even, for I think f or NASA. I canít remember what the other things were, except that generally, to be able to put together an area scanner like this, was a good thing, to be able to map out, oh, galaxies, quasi-stellar objects and things like that.

Weart:

And he had this CAT? What is that?

Cocke:

Yes, the CAT was a small computer. CAT stands for Computer of Average Transience. Itís really just a signal [???] device. Really no more than a sophisticated multi-scalar, as used often by nuclear physicists.

Weart:

In fact these things were actually developed for nuclear physics research werenít they?

Cocke:

Yes, right, for nuclear physics and also I think for biology.

Weart:

I see, so you approached him and invited him to join your research?

Cocke:

Sure, yes, uh huh.

Weart:

What did he feel about it? Did he feel optimistic? Did he think you had a good idea or what?

Cocke:

Oh yes, he thought that was a good thing to do. None of us really were very optimistic. We looked upon it more as an, idea -- well, as an opportunity to, as I said, get to know how to work the telescope, and generally to get into astronomy a bit, observational astronomy, and get a better feel for what actually went on at the telescope.

Weart:

And also along the way you also learned about Taylorís electronics? Cocke Right, yes, definitely. Definitely.

Weart:

Did that take some doing? Here you are, youíve been doing theoretical work all the time and now here you are youíve been faced with some rather sophisticated electronics.

Cocke:

Yeah, that was a bit of a mess. It would, even --

Weart:

Did this thing -- was this thing a pulse counter or how did it take the multiplier out correctly?

Cocke:

Yes, it was -- well, no. Letís see if I can remember properly. The apparatus that we use today for this kind of work is a pulse counting apparatus, which directly counts, multiplies pulses and then distributes them, and. then the multichannel analyzer, the CAT, distributes them into the various bins according to where, you know, according to what time it is, so as to build the light curve [???]. Right, so as to build the light curve up. But, at that time, we were using a device called a -- 00 -- a current frequency converter, right, yes, uh huh -- yeah, it --

Weart:

A current frequency converter, and then the CAT went ahead and digitized the frequency I suppose?

Cocke:

Yes, actually, the frequency was digitized already, coming out of the current frequency converter, it was in the shape of square pulses. And so, the current coming into the current frequency converter, from the photo multiplier, was conversed into a string of pulses.

Weart:

Right, I see and for your photo multiplier you used one of these good old lP2ls and that was Taylorís too? Did you cool it or anything like that?

Cocke:

Yes, right, uh huh, right. Yes, we cooled it with dry ice.

Weart:

You know usually when somebody starts working with one of those things they run into a lot of problems with shorts and so on. Did you have any problems that way, leakage currents? Moisture?

Cocke:

No, we didnít. The photo multiplier had already been de-bugged for us by -- well, really, I suppose ten years of use by astronomers, on --

Weart:

I see so you were really using some very standard equipment around the observatory?

Cocke:

Yes, the photo multiplier itself, and the current frequency converter, were already pretty thoroughly tested out. So we didnít have any trouble on that score.

Warnow:

What did you see when you looked at the CAT screen ad this comes up a good deal on the tape. I think itís important to have you describe the kind of things you were looking at whether itís now or later when we are talking.

Cocke:

Yeah, I can do that. This, what you see on the CATís screen is a representation of what is in the, at the time, in the memory in the computer. You see sequentially, well, each little memory counter, as it were, is represented on the screen by a dot. And the height of the dot above the baseline is proportional to the number of counts that are in that address in the memory. Ok. So you see, really, itís sort of a diagrammatic representation of the number of counts, in each of the elements in the memory.

Weart:

What did it look like on the nights that you were observing?

Cocke:

Well, --

Weart:

What did the set appear like? I am trying to picture; here is the observatory, etc. What did the whole set up appear like?

Cocke:

Yes. Well, the general setup for the electronics was, several instruments stacked one on top of the other. We had counters, and frequency synthesizer, and then this CAT, and then this associated interface equipment, all, piled up on a desk, as I remember. We -- the CAT was sitting right in the middle of things, and on the screen of the CAT -- the CATís screen is a circular screen about, oh, Iíd say about five inches in diameter. It looks very much like an oscilloscope screen, except that it is circular or square, I canít remember now. Yeah, I think it is circular. Anyway, what there is then on this screen is a display, which looks as I say very much like an oscilloscope screen.

Weart:

A wiggly line?

Cocke:

Yes, right, only instead of being a real wiggly line, you can see itís all broken up into dots, and each dot then represents the level of counts in the particular address in the computer.

Weart:

I got the picture ok. So then you still had this telescope time left over from when you were thinking of looking at the white dwarfs, is that it? Or did you apply again? What happened?

Warnow:

Letís have the dateÖ

Weart:

Friday December 10th.

Cocke:

Right. No, this was the same telescope time. Right. Well, what happened was that we went up there, and after a -- ok, let me have just a second here, let me look around for a date -- ok -- right, on December 10th, that was a Friday. We all went, all three of us went up to Kitt Peak, and Don Taylor and Bob McAlister, who is the night assistant, worked around with the electronics, I remember, while Disney and I turned our attention to the telescope itself and were doing -- I recall, we first had to do a lot of calibrating on the offset guider. The problem was that Bottaís Star was just too faint to be seen directly with the eye, at the 36 inch telescope. Did I say 90 inch telescope at some point? 36 inch, yes. Anyway, so not being able to see this thing with the telescope, we had to develop a method -- well, we had to use a rather well known method called offset guiding, by which one offsets, by using a sort of rectangular micrometer setup, at the telescope, from a star which you can actually see and whose position you know, and from which you know the distance to the object youíre interested in -- in our case, the pulsar. So, Disney and I checked that out, and McAlister and Taylor were tuning the electronics up. Well, the first night, I don t think we did very much. We were occupied mostly with checking the equipment out and getting things set up. And then the following night, that would be the 11th, we actually did do some observations.

Weart:

What was it like, these were your very first observations with a substantial telescope, and did it make some impression on you?

Cocke:

Oh yes, I remember being rather scared and depressed by the whole thing. Well, neither of us thought that we would get anything from thisÖI remember at a conference, a month or so before, that I had gone to, one of these Texas symposia for relativistic astrophysics, -- I remember asking a couple of very well known, very prominent astrophysicists who were there, asking them whether or not they felt that the pulsar would ever be detected optically, and they all were very, very negative about it, and they said, ďOh no, I doubt very much if that will ever happen.Ē But --

Warnow:

I want to make a quick check on what we are doing on the tape, how much tape is left on the reel?

Cocke:

Ok, on my reel I have, Iíd say, about 30 percent left to go.

Warnow:

Ok. Good. Wonderful.

Weart:

I still havenít quite gotten the answer to my questions. I wondered just what you felt just about being there working with the telescope, then the dome opens then you see the sky.

Warnow:

How did Disney feel?

Cocke:

Yes. It was very exciting, but I was quite nervous, and I had the distinct feeling of wondering, really, what in the hell I was doing there. Disney, I think, was a bit more jovial about the whole thing. He was -- Disney was more optimistic than I was, I remember.

Weart:

What you were saying applies very much through the next couple of nights?

Cocke:

Yes, pretty much. Pretty much. It wasnít until we proceeded -- the first night was spent checking things out. The second night, we actually did some observations but as it turned out, I had made a mistake in computing the Doppler shift of the pulsar period, due to the earthís orbital motion, and so even though we had actually sat right on Bottaís star, and taken observations, we didnít have the frequency or the period set correctly into the frequency synthesizer, which we were using, which we used as a trigger to the CATís memory.

Weart:

The frequency had to be on very precisely to observe anything.

Cocke:

Yeah, the frequency had to be to within, oh, one part in a million, to be able to see anything.

Warnow:

Of course you didnít know that at that time did you?

Cocke:

Well, we did, yeah, because we could --

Warnow:

I mean you didnít know you had made a mistake in the calculation at that point?

Cocke:

-- right, sure, we didnít -- yeah. So we wasted one, I think probably a whole nightís observations, in one way or another, because this frequency computation had been mistaken.

Warnow:

Well I have before me the little article you wrote for Maglishís Journal and that was true of the 11th when you could observe and you had negative results.

Weart:

Right, the 11th and the 12th.

Cocke:

Right.

Warnow:

But now something new happened on the 12th because Taylor wasnít there. What was Taylor doing on the night of the 12th?

Cocke:

Well, no, Taylor was the only Ė

Warnow:

I am just trying to get a feel for each night, the three of you how you worked there?

Cocke:

Well, what was Taylor doing that evening? Well, yeah -- as a general thing, Disney and I were working with the telescope itself, whereas Taylor was off to one side of the observing platform, doing the electronics.

Weart:

Did you have any trouble when he left you with all these electronics?

Cocke:

No, we didnít. He had things very well set up for us, and with instruction sheets that even an idiot could have followed. See, once the electronics get set up, itís pretty much just a fairly routine thing to work them. Itís the setting up and the actual preparation that took so much time.

Warnow:

Well then on the l2th, Taylor is not there but you donít have problems with the electronics.

Cocke:

Right, uh huh.

Warnow:

But you still have those faulty calculations that you havenít discovered yet?

Cocke:

Right, uh huh.

Warnow:

And on top of that itís beginning to cloud over, now how do you feel at this point?

Cocke:

Well, we feel very discouraged, yeah. Itís a bit hard to cast back my memory and think and remember what I was feeling like at that point. I do remember feeling pretty discouraged about the whole thing. Of course, we werenít very optimistic to begin with, really. I wasnít. And so, we -- I wasnít feeling as discouraged, as -- I was not feeling as discouraged as I would have if Iíd had really, high hopes.

Warnow:

Right.

Cocke:

But anyway, the next two days then were spent more or less walking around the mountain under the clouds, trying to think what to do next until then I remembered that it would probably be a good thing to go and re-check the calculations that I did. So -- I --

Weart:

Just the feeling you had.

Cocke:

Yeah, uh huh, fine.

Warnow:

And also you are walking along with Disney I suppose, and talking it over?

Cocke:

Right. Sure. Sure. Uh huh, yeah. So anyway, having, gotten -- sorry?

Weart:

Was it raining then?

Cocke:

Yeah, I think on and off it was. It was very foggy up there, as I recall. I remember one evening, going over to the Kitt Peak National Observatory, dining room, to see if we could find anybody over there that we knew. Stewart and Kitt Peak are pretty close to each other. Theyíre about 100 yards, 200 yards apart. And Kitt Peak is bigger and they have a regular dormitory, well, a rather more organized kitchen type arrangement than we do. So anyway, we went over there and talked, found some people we knew and talked with them, and then, on the way back, it had gotten so cloudy, so foggy -- this was in the middle of the night now -- that even with a flashlight, we could not find our way back. And I remember it taking us probably about an hour to work our way back through that 200 yards, to the Stewart Observatory dormitory complex.

Weart:

Thatís a bad observing night.

Cocke:

Oh, it sure was, boy. Uh, huh. But at least, we did get the calculations corrected, and then, -- yeah, well, it was an error of 2 pi, actually. I had, had mistakenly approximated the sign of an angle by the angle divided by 2 pi and so --

Warnow:

How did you feel when you found that error? Cocke I felt like a real idiot. And I was a bit dumbfounded, because now, having gone through all that time to make these observations, now I was faced with the prospect of having to go back and do the whole darned thing over again, again with the feeling that it was utterly futile anyway, and that -- really, the whole thing was a waste of time. But, --

Warnow:

You had two days when you...the 13th and the 14th, was it on the 14th when you worked on the calculation and found your error?

Cocke:

Well, I donít remember. That would hard to reconstruct.

Weart:

Itís of interest because you said your run was due to finish on the 14th but then somebody gave you a couple days following.

Cocke:

Yeah, right. One of the other astronomers down here, whose name was Bill Tift, whoís Still here, at Stewart, was going to do some preliminary observations, using, oh, an area scanner I think that he had developed I canít remember exactly what. But as it turned out, Tift very kindly offered to let us take over his nights, take over two of them, to --

Warnow:

How did you persuade him?

Cocke:

Well, we just called him up on the phone and said, ďPlease, Bill, canít we do this? Weíve discovered this mistake we made, and we want very much to go over and be able to do the whole thing over again.Ē And he said, ďWell, ok, go ahead.Ē So he was very good about that.

Weart:

So now we come to the night of the 15th?

Cocke:

Right, ok -- the night of the 15th. That was the same, well, the same setup, only weíre doing the whole thing over again, but with a different period setting for the pulsar, and we, once we got back onto Bottaís Star again, using the offset guider again, we saw the pulse come up almost immediately. And we were both, both Disney and I were completely dumbfounded by the whole thing. Taylor --

Weart:

You hadnít expected it.

Cocke:

-- well, no, we hadnít. I think Disney again was still more optimistic than I was, but I was really, really dumbfounded and thunder struck by it. Taylor unfortunately was downtown at the time. He had to go back to administer a final examination to one of his classes, I think.

Warnow:

Now I think on the tape by the way you referred to Bottaís star as S.P. star.

Cocke:

Right.

Warnow:

Letís make a connection there with your voice somehowÖ..

Weart:

Yeah, what does that mean?

Cocke:

Yeah. Well, S. P. means South Proceeding. As it turns out, the center of the Crab Nebula, thereís a double star, and Bottaís Star is the South Proceeding component of that double star. The other component of the double star, the North Following star, is not connected at all physically with the Crab Nebula. Itís probably a star thatís being seen through the nebula, and is thus way, way on the other side of the nebula, and thereís no connection at all with it. South Proceeding star? Yes, itís the southward component of the double star, and it precedes the other component, which means that itís to the west of it and precedes it in its motion across the sky. As the earth turns. Right.

Weart:

Now I donít think we have in your voice yetÖ.

Cocke:

Whatís that again, Spencer?

Warnow:

What we need you to do is to make the connection between Bottaís star and S. P. star so that the students listening to the tape, the discovery, tape know what you are looking at when you say that this is observation 22 on we are on S.P. star etc.

Cocke:

Right.

Weart:

Right.

Cocke:

Right, ok -- the S. P. star is Bottaís star. Itís the same object. Ok.

Weart:

Ok. Thatís all we need.

Warnow:

On the first run? Itís the very first run of that evening you find what you are looking for?

Cocke:

Well, the second run, actually. The first run, we do on the sky, just to see what level of light is coming from the [???].

Weart:

Ok. So then the second time you saw it and then you thought it might be some kind of an artifact you said.

Cocke:

Yes, well, we had to check and make sure that it wasnít something, some peculiar thing with the electronics, so we --

Weart:

Were you really skeptical? Did you think it as likely that it was in the autonics?

Cocke:

I thought, well itís hard to say really just how skeptical I was. Having seen it, pop right up, right when we set on Bottaís star, was really quite a -- quite an illumination. And, I wanted to make sure, before we announced it, that it was in fact the real thing. So it wasnít just an expression of skepticism, but rather, you know, part of what one should have done, as being good scientific observing practice.

Warnow:

Whatís the secondary pulse you found 180 degrees out of phase?

Cocke:

Yeah. The Crab pulsar has two pulsars in it, a big one, the primary one, and a shorter, fatter, secondary pulse. They come more or less spaced evenly between each other.

Warnow:

And you had expected this?

Cocke:

Well, we werenít sure. The radio pulse looks like that, and so we had felt probably thatís what the optical pulse would look like too.

Weart:

So what kind of checks did you do then?

Cocke:

Ah, letís see -- ok, 21, weíre still on the SP star, on Bottaís star, but we changed the frequency, No pulse appears. Ok. Then on --

Warnow:

And by now you are beginning to get quite excited although that is not on the tape.

Cocke:

-- right, definitely, yeah, sure. Sure. Ok, then for observation 22, we, I think we steered the telescope off the South Proceeding star, the SP star, but then reset the proper frequency back in, and again, no pulse appeared. And then --

Warnow:

Right before observation 22 the engineer there is so excited? MacAlisier?

Cocke:

Hm, mm

Warnow:

He is obviously so excited and thatís why he put the tape recording machine to the wrong position?

Cocke:

Well, the tape was running improperly long before that. The tape starts on observation 18. Ok. When we first discovered it. So this was before the thing had been discovered, when the mistake was made, about the tape recorder.

Weart:

Oh, I see, observation 18 was when you start to see the pulse coming up?

Cocke:

Well, that was either 18 or 19, letís see, I canít remember. Letís seeÖ

Warnow:

We really need some copies of your notes so that we can see what you are excited about at observation 18.

Cocke:

Right. Oh huh, sure. Sure.

Weart:

Oh but at any rate the important thing is that the tape was already running when you first saw the pulses coming up?

Cocke:

Well, letís see. I think the first thing we did was to move off Bottaís star, off somewhere in some other part of the nebula, and then do the whole thing over again. And we did that and we discovered -- nothing. No pulse at all. And then -- yeah, just background noise, right, uh huh. Then we moved back on Bottaís star again, but this time we changed the frequencies, so that the computer was not running synchronously with the pulsar, and so we did that, and then we found that there was no pulse there, as we would think, as we would expect. Then, still being on Bottaís star, we cut the proper frequency back in, and then, the pulse came up again.

Warnow:

Ok, now when the tape begins on observation 18?

Cocke:

Hm mm.

Warnow:

I am trying to remember now I did take notes and I donít know what I did with them?

Cocke:

Hm mm.

Warnow:

But on observation 18 you are doing one of those tests. On observation 21 you are on the S.P. star but youíve changed the frequency.

Cocke:

Ok, that sounds as though it might be all right.

Warnow:

And on Observation 22 which is where the tape begins?

Weart:

Yeah, here it is on opposite page they changed the position.

Warnow:

Right. You got the right frequency, but youíve changed the position to north of S.P. star?

Cocke:

Right, yeah, uh huh. In fact, the first observation that we did that evening was of the sky, and if I remember correctly, the tape was running then, in the sense that we were -- yeah, right, Iíve got the transcript right here in front of me. We begin the evening with observation 17.

Weart:

Oh, I see, 17 was the sky and 18 was the one where the pulses appeared?

Cocke:

Right, yeah, uh huh.

Warnow:

Oh, in other words this is not the 17th and 18th observation of the night but of the whole series?

Cocke:

Right, yeah. Now, folks, weíre just about to run out of tape over here, Iím going to have to turn it over. Ok, it will take me just a couple of minutes. Hang on.

Cocke:

Ok.

Weart:

Ok, we are just about finished actually. I guess the only question I have then is what did you do after you were sure that you had it?

Cocke:

Well, after we were sure, I think we called Taylor up and told him, and then we called our wives up and told them, and Taylor was very skeptical. He was even more skeptical than I had been, and of course, by then I was utterly convinced that we had it, and so, what we did was, we then made just a continuing series of observations throughout the night of it; of the pulsar, in various colors and things like that, and then we -- closed up shop and went to bed. And then the next day, we got up, the next evening, Taylor came up, and we set things up again and did another run or two for him, and I think he probably did some more tests then himself. So then, he was convinced that what we had was the real thing.

Weart:

What were your wives doing all this time by the way? Here you were working nights and I suppose sleeping during the day?

Cocke:

Yeah, trying to -- itís really hard to sleep in the daytime. Thatís one difficulty astronomers have. Itís very hard to go to sleep in the daytime. At least it is for me.

Weart:

Did they have darkened rooms up there?

Cocke:

Yeah -- oh yeah, sure. Yeah.

Warnow:

Well the fact is you were convinced by the end of that evening werenít you?

Cocke:

Right, oh definitely, yeah, uh huh. Sure.

Warnow:

And you must have had a little celebration? No?

Cocke:

Well, yeah. I remember a couple of days later, after things had quieted down a little bit, our wives came out, and we -- oh, they cooked a special dinner for us with wine and things like that, and it was really, really, all very, very cordial and very exuberant.

Weart:

Now tell me this discovery was really something that you did originally fairly casually. Do you think it made a big difference to you personally?

Cocke:

A big difference, personally -- yes, I would say that it has. It gave me a taste of what itís like to do something really, really exciting and interesting. And it also sort of brought me into the general feeling for what happens when you do something really good like that.

Weart:

Well what kind of experience did you have afterwards?

Cocke:

Well, afterwards. You mean, with other things, then?

Weart:

No, no, I mean as result of this observation, did it change peopleís relations with you? Did it change the way you felt about astronomy?

Cocke:

Oh yes, after that I became much more optimistic about things that I was doing and things that other people were doing, and I felt that really, you only had to look in the right places and look often enough and youíd find something. Thatís --

Warnow:

And how about take some risks too?

Cocke:

-- yeah, oh, definitely, sure. You canít ever do anything big like this without taking risks.

Warnow:

I am very pleased. I think we are going to have a lot of material here to work from. Do you think there is anything else we should be covering in this tape in terms of your whole experience? Are there any questions you wished we had asked?

Cocke:

Well, letís see, Joan. Anymore questions to ask? Gee, I really canít think of anything.

Warnow:

It seems to me though, once you had made the corrections in your calculations everything just went click, click, click, right?

Warnow:

Right in the right slot from there on in?

Cocke:

Yeah, definitely. From then on, everything behaved quite as -- almost perfectly.

Warnow:

Uh huh.

Weart:

Because it was there. Why did you think that nobody else had observed it? Why do you think you were able to do it when others hadnít?

Cocke:

Well, in fact, if we hadnít done it, other people would have, Iím sure, later on.

Warnow:

Did you ever talk to those noted astrophysicists that were so doubtful? From the Texas conference?

Cocke:

Yeah, uh huh. I remember talking, reminding one of them later on what he had said, and he was really -- he felt very sheepish about it.

Weart:

Do you have any idea why? It would have been fairly easy for anybody to have looked. I remember thinking at the time myself why how stupid, anybody could have planted the thing at Bottaís star. Do you have any feeling why it hadnít happened?

Cocke:

Uh huh. Yeah, it was -- since the discovery of the radio pulsar, until the time that we did the observations, it had really been only a month or so, or six weeks, and it takes a fair amount of time for things to get going and get geared up to do things like that. So, in fact, --

Warnow:

In some way you had partially been revved up then, to do an experiment anyway?

Cocke:

Yeah, thatís true. We had a lot of the instrumentation together already. Or at least the ideas were together.

Warnow:

And the connection with Taylor was already there?

Cocke:

No, I think the connection with Taylor was established after we had, after the pulsar -- after the radio pulsar had been discovered.

Weart:

One thing then you knew you had to have much faster electronics I suppose?

Cocke:

Thatís true, right, Well, that was one thing that would have stood in the way of other people doing the measurement, namely, that the sort of observation, the sort of thing that people had been doing before, to try to detect optical pulses, might not have worked for this, because the pulses were so fast.

Warnow:

And then one more question, you had already scheduled the time to use the 36 inch telescope?

Cocke:

Right, uh huh.

Warnow:

How long do you normally have to wait? After you apply for use for a project?

Cocke:

Well, you can wait up to three months, I suppose.

Warnow:

I see, so that gave you another time edge?

Cocke:

Yeah, right, we already had the time, but at that point, the 36 inch was not, in terrible demand. The instrument -- a lot of the instrumentation for it, as I remember, was just being developed, and was on a somewhat experimental basis. So, although the telescope itself had been up there for, oh, Iíd say about 10 years or so, the newer electronics and the newer instrumentation of or it was just then, being developed and so the telescope was not yet being used regularly on a -- a sort of production run basis.

Warnow:

Yet astrophysicists at other observatories would have had that time lag?

Cocke:

Quite possibly, yes, quite possibly. But really though, for a project that is of immediate importance, itís possible to short circuit a lot of that. You can go to the director of an observatory and say, ďLook, weíve got to do this, so and so has just discovered something, we want to follow up on it and make additional observations, or doĒ -- you know, something else.

Weart:

But you didnít have to do that because your time was already scheduled?

Cocke:

Yeah, our time was already scheduled. Thatís true, yes, uh huh.

Warnow:

One other conclusion seems to be that other people didnít see the connection that quickly.

Cocke:

Well, I think thatís probably possible, yeah, uh huh.

Warnow:

One other thing -- are you going to be able to send me photographs?

Cocke:

Yeah, sure, uh huh. Oh -- well, actually, letís see -- I think the best one to do would be this one thatís in [???] thing. I havenít looked for that yet. I presume itís in the archives here at the university.

Warnow:

Could you do that? Could you check that one out? Otherwise Iíll try and get it through Maglish I guess or something like that?

Cocke:

Yeah, sure, [???] would have a copy of it.

Weart:

And anything else, pictures of the observing room, you know, the observing chamber, inside the dome anything that gives some feeling of the physical setup and what you look like.

Cocke:

Uh huh.

Weart:

You and your wife maybe?

Warnow:

The CAT screen in action maybe?

Weart:

Weíll send them back.

Cocke:

OK, yeah, I do have a picture -- all right, fine. Sure.

Warnow:

And I think I may also end up by asking you to have someone out there take a role of films of you because we will try to have a number of slides. You know walking along with somebody.

Cocke:

Hm mm.

Weart:

And see what you look like.

Cocke:

Ok.

Warnow:

Or at the telescope or whatever? Could you arrange that?

Cocke:

Uh huh. Yeah, I can probably do that, sure, uh huh. Yeah.

Warnow:

Ok, alright, in fact why donít we consider that a request now?

Cocke:

Ok, fine, sure --

Warnow:

Because we need quite a few slides if we are going to darken a room, otherwise students tend to fall asleep.

Cocke:

Ok, sure. Yeah. Youíd want slides then just of me personally and of the telescope?

Warnow:

Things that you could imagine would be suitable, itís going to be you mostly.

Cocke:

Uh huh.

Warnow:

You with the telescope.

Cocke:

Uh huh.

Warnow:

A picture of the CATís screen. You know, with the pulses on it, I donít mean to make this a big production but just to give them a feeling of what it is you are doing.

Cocke:

Ok, sure. Sure, Ok, yeah.

Warnow:

MacAlister, if he is around, and could have his picture taken.

Cocke:

Uh huh. Uh huh.

Warnow:

At the tape recorder.

Weart:

Really if we could we could use pictures of Tiff and of Weyman all the names weíve mentioned here.

Cocke:

Uh huh, Ok. Yeah, Iíll see if we can do that. Sure. Ok, now -- you want color slides then?

Warnow:

It turns out that we might want color slides. They are just as cheap. I thank you very much sir.

Cocke:

Ok. Sure, sure, Ok. Yeah, Ok, Joan, sure. Right, Ok, now --

Warnow:

And now you are going to mail this? How about mail it return receipt requested so the post office is more careful?

Weart:

Mark it tape recording.

Cocke:

Ok, fine, will do. Ok, now, let me make sure what Iíve got to do there. Iím going to stop my tape, Ok, because this is....