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Oral History Transcript — Dr. John Scoville Hall

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Interview with Dr. John S. Hall
By David DeVorkin
At the Yale University Observatory
February 21, 1979

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John S. Hall; February 21, 1979

ABSTRACT: Interview discusses John S. Hall's early interest in astronomy; comments about family background and early childhood, schooling in Connecticut and college training at University of Amherst and Yale University. Early contacts and interests in photoelectric photometry, his pioneering efforts in red sensitive cell photometry, work at the Radiation Laboratory at MIT during World War II, postwar research at the Naval Observatory and his co-discovery of interstellar polarization. Also prominently mentioned are: Solon Bailey, A. L. Bennett, Subrahmanyan Chandrasekhar, Thomas Cochran, Robert H. Dicke, Harold Ewen, Fresnell, Green, Jesse Leonard Greenstein, Ejnar Hertzsprung, W. A. Hiltner, Gerald Edward Kron, J. A. Miller, Prescott, Jan Schildt, Frank Schlesinger, Harlow Shapley, Theodore Stoller, Otto Struve, David Todd, Robert Williams Wood; Amherst College Observatory, General Electric Co., Harvard University, Lawrence Radiation Laboratory, Science (journal), Sproul Observatory, United States Navy, and Yerkes Observatory.

Transcript

DeVorkin:

I'm interested primarily in discussing your own life and your own direct recollections, but we can preface this with a few remarks about David Todd.

Hall:

There are many things about Todd that are very amusing.

DeVorkin:

Did you know him at all? Was he still around Amherst?

Hall:

No, but he was alive. I think he was in a mental institution at the time in Belchertown.

DeVorkin:

Really? In Belchertown. Do you know why?

Hall:

Well, he had certain peculiarities. I don't want to put them on tape.

DeVorkin:

All right. We won't.

Hall:

You wouldn't publish them anyway.

DeVorkin:

No. certainly, and anyway you have editorial control over this material. If anyone wished to use it, they would have to contact you or your designated people.

Hall:

All right. Fine.

DeVorkin:

Now, in the seminar or colloquium that you gave yesterday[1], which I've heard most of now on tap, in discussing your early education, you identified that the total eclipse of 1925 was what brought you pretty much into astronomy. And then winning the prize at Amherst, for the princely sum of ten dollars.

Hall:

There was another source, too.

DeVorkin:

Source of funding?

Hall:

No, no, another reason, but maybe you don't want to go into that.

DeVorkin:

Well, yes.

Hall:

Everybody has reasons.

DeVorkin:

I would be interested in your reasons.

Hall:

Well, when I was 13,14,15 years old, we'd skate on a pond about a mile from home, and during Christmas vacations, a young man who was studying at New York University would visit a neighbor. And he was very much interested in astronomy. He had studied astronomy formally or had read about astronomy. When we went home from skating, the stars were out at that time of year, and he would point out various stars and planets and tell us about them on the way home.

So this got me very much interested, and 45 years later, I was in Philadelphia and went out to his home in a suburb of Philadelphia; visited him and his wife, and told him about this. Be was very much pleased. He was still very much excited about astronomy, only this time he asked me questions, instead of the other way around.

DeVorkin:

What was his name?

Hall:

His name was Thomas Cochran, and he was Benjamin Franklin Professor of History at the University of Pennsylvania, so he had had a very distinguished career.

DeVorkin:

That's how he ended up, not in science.

Hall:

That's right. But he was interested in everything. Very enthusiastic about everything. This has a lot to do with it, of course.

DeVorkin:

So there were these three reasons.

Hall:

The three, yes.

DeVorkin:

That's good to identify. Could you give me an idea of what your background is, what your father did as you grew up?

Hall:

I was brought up on a arm. But my father went into the candy business, and manufactured so-called Hallmark Chocolates. First they were Farmhouse Chocolates, and he sold that business out and started another one. And then at one time he went into the toy business, made his own dies and this sort of thing. I saw him doing this. I was quite interested in doing things with my hands, mechanical things.

DeVorkin:

So you did have contact with tool and die work?

Hall:

Well, yes he had in fact a crude machine shop.

DeVorkin:

This was in Old Lyme, Connecticut?

Hall:

Yes.

DeVorkin:

Did these businesses prosper? Was your family stable financially?

Hall:

Yes and no. It was up and down. He heavily mortgaged his farm, but he paid the mortgage off completely the week before he died, 1948. But I suppose we were stable. I had two brothers, and he didn't have money to put me through graduate school. He helped me get started the first year in college, and after that I pretty ouch earned my own way. Professor Green gave me a position at the observatory. And then, I had a little shop of my own in the fraternity house, so that I was able to get through college, together with what I earned in the summers.

DeVorkin:

What was this shop?

Hall:

Well, I sold cigarettes and candy and so on to the fraternity brothers.

DeVorkin:

That's interesting. What was your grade school experience like? Was it public schooling?

Hall:

Yes, all public schooling.

DeVorkin:

All in Old Lyme?

Hall:

Grade school, yes. For high school, we had two years in Old Lyme, two years at Pratt High School in Essex, and then I tried to get into Amherst, and my grades weren't good enough, so I took a year at Morgan High School in Clinton. Then I was certified into Amherst. In Amherst, I had a hard time the first year, but after that I did very well. I actually graduated cum laude and made Phi Beta Kappa. And my thesis was in astronomy. I had a project in astronomy, determining sextant errors, but my majors were in mathematics and physics.

DeVorkin:

Now, Green, as I recall from your comments yesterday, had a lot to do with bringing you to Yale.

Hall:

Yes.

DeVorkin:

And there were research interests that were active here at Yale similar to yours. You had research experience at Amherst that helped you begin at Yale? Is this correct?

Hall:

Well, Green, wrote on my behalf to many graduate schools. There were only a half a dozen at that time that were really active, and the only one that offered assistance, financial assistance, was Yale. Harvard would hire me part time, but it would take me many years to get the degree, which I didn't want to do if I could help it. While at Amherst, I went to a public lecture, in my junior year, I think it was, in Springfield.

One of the physics professors took us down — a group of us who were majoring in physics — and there was a man from the Bell Telephone Lab who gave the lecture, and he had a light beam going across the room, and showed how voice could be transmitted with light, using a photoelectric cell.

DeVorkin:

Was this your first contact with a photoelectric cell?

Hall:

First contact with the photoelectric cell.

DeVorkin:

Do remember the year of that, at Amherst?

Hall:

Well, I think it was probably 1929.

DeVorkin:

Do you remember the lecturer?

Hall:

I don't think it was the same man that developed the cell. I think it was someone else from Bell Telephone.

DeVorkin:

Yes. Probably so. any case.

Hall:

No.

DeVorkin:

Then your next contact with photoelectric cells was through Schlesinger's son?

Hall:

Schlesinger produced one from his desk when I visited the Yale Observatory in May 1930 which had been given to him by his son, Wagner Schlesinger, who later was head of the Fels Planetarium, also the one in Chicago, the Adler Planetarium. He's now died, I think.

DeVorkin:

What was his background that he would have contact with the photoelectric cell? I think you mentioned, it was a friend of his?

Hall:

Yes, he roomed with Prescott at Yale.

DeVorkin:

That's the contact. I see.

Hall:

Yes. He was his room mate.

DeVorkin:

Oh, that's good. That's a great contact.

Hall:

Yes, I should say so.

DeVorkin:

Yes. Now, Frank Schlesinger himself of course was always, from what I know of his career, very interested in innovative technique.

Hall:

That's right.

DeVorkin:

That's known in astronomy.

Hall:

Have you read the memoir by Brouwer?

DeVorkin:

Yes, certainly. Talking about Schlesinger, he was always very interested in spectroscopy.

Hall:

Of course, he invented many new things in spectroscopy. His method of computing the orbits, using the method of the least squares, was a great improvement over the pedestrian ones that has preceded it.

DeVorkin:

That was the Lehman-Files?

Hall:

His was the differential method.

DeVorkin:

His was. Yes.

Hall:

He was great for taking out unnecessary figures in computation. He would use differences instead of the real figures and this sort of thing, to simplify computations.

DeVorkin:

You talked quite a bit about Schlesinger and gave a very nice series of recollections yesterday.

Hall:

Hell, I knew him better than the others. He and Brown were the giants at the Yale Observatory. But I have not made an exhaustive study, and there are many more people probably that came to this country for short times. These are the ones that I know about from Yale during my years here.

DeVorkin:

Did you have contact with De Sitter?

Hall:

I saw him at Yale. But not directly, no.

DeVorkin:

He gave the Sillman Lectures, was it?

Hall:

He may have. He was a great friend of Schlesinger's.

DeVorkin:

Talking about Schlesinger, there is one particular contact that I would like to know about. Later on in the thirties, he became instrumental in bringing over war refugees, astronomically trained people for jobs.

 

Hall:

Yes. Hertz was one.

DeVorkin:

Was he doing any of this actually in the early thirties while you were at Yale?

Hall:

I didn't know of it. No. Hitler was not in the forefront at that time.

DeVorkin:

Right.

Hall:

Incidentally, in connection with Rolland, De Sitter and so on — there was an IAU meeting in Leiden, and he recalled an incident as he was leaving Leiden on the train, there were various hawkers going along the platform, and the hawker would have different things which he would offer to the various people through the open windows.

One stopped in front of his window, and said, "Gum?" Chewing gum. He could recognize that he came from the United States so he tried to sell him chewing gum, and this amused Schlesinger, that without saying a word or anything, he was offered chewing gum.

DeVorkin:

He seems like quite a fascinating man.

Hall:

He was. Very interesting man.

DeVorkin:

What is your knowledge of his eventual work on behalf of refugees? Could you give me an account of that?

Hall:

Let's see, Gustav Land came. Garfinkel was American-born I think. No, I can't give you that because I was in Swarthmore at that time.

DeVorkin:

Right, At the time of doing your thesis, there could not have been very many people working in photoelectric techniques at that time. But certainly Stebbins was. Did you have contact with Stebbins, any contact directly or by letter?

Hall:

Yes. I'd say it was sort of a long story, unfortunate in a way, but it ended nicely. I didn't want to get into it yesterday because it would have taken too much time. Schlesinger had written to Stebbins, saying that he was thinking of asking a graduate student to take on photoelectric photometry at Yale, and he wanted some advice. Stebbins wrote back saying that that person would rue the day that he was born if he took up this field.

DeVorkin:

Really?

Hall:

Schlesinger interpreted this remark to mean that Stebbins didn't want other people entering the field. He dominated the field. He was the father of photo-electric photometry and deserved full credit for that. Rut later I found out that Stebbins was right. It became extremely difficult to use an electrometer under the conditions in which observers had to use them in those days.

I was lucky in a sense because my equipment was fixed, but when you had it on a moving telescope, you had the problem of the needle drifting because of the motion of the telescope, and so on. And you had to use it at the highest possible sensitivity because you -had no electronic multiplication.

DeVorkin:

So you used the Loomis Tower Telescope.

Hall:

Yes. I was the second person to use it. (Carl) Stearns was the first, and his thesis project, I think, began with the idea of using it for astrometry, but he found that it was unstable or something. He couldn't get sharp images. And so he did, I believe, a problem in photographic photometry with it. Stearns was at Yale as an assistant for about five years, '20 to '25, I think, and got his PhD on that work with the Loomis Telescope.

DeVorkin:

That's fascinating. The Loomis still exists out in Bethany. Now it looks at the Pole.

Hall:

I don't know the history of that telescope. Schlesinger wrote a one page paper which you probably have seen. But it's not very detailed. He insisted that I put the Loomis name in my thesis, and I believe there was some feedback involved in that, and that was why.

DeVorkin:

Yes, that was the bequest. One of the telescopes from the bequest.

Hall:

Yes.

DeVorkin:

It's certainly a unique instrument. You were here then of course when the Tower was up and everything, on the hill.

Hall:

Yes. Oh yes. Actually in those days, as I mentioned, one had to go down to wind the clock every two hours. It was a 60 foot tower, and I had an aviator's suit made of leather, and I had heavy boots. 50 my suit weighed 17 pounds, and I suspect, with the hoots, I had 20 pounds of extra clothing. And on long winter nights, it was quite a lot of exercise.

DeVorkin:

So at this point, after Schlesinger received that letter from Stebbins and misinterpreted it, you had no further contact with Stebbins?

Hall:

I had no contact but of course, I read carefully what he'd done, because he was the pioneer, not only in the United States, but in many respects in the world. He did his selenium work with which he discovered the secondary minimum of Algol in 1911. Then Gutnick and Rosenberg did some photoelectric work in 1914-15, or thereabouts. Gutnick at Potsdam and Rosenberg at Tuhingen.

DeVorkin:

That's the same Rosenberg who worked for Hertzsprung, I believe?

Hall:

It may be. He was an independently wealthy man.

DeVorkin:

Was he?

Hall:

I believe so. I think he had his own equipment at the University of Tubingen. I get this all by hearsay.

DeVorkin:

It's good direction for me to track this down.

Hall:

Yes. Now in 1931, after I had carried through the basic work which showed that one could use Prescott's suggestion of cooling, Stebbins published a paper in the ASTROPHYSICAL JOURNAL describing the photo-electric photometer he'd designed.-for Yerkes, involving the Lindemann Electrometer. And in that, he said he had tried other commercial photo-electric cells, but the dark current was so high that it impossible to make any measurements. Well he didn't have Prescott working for him — everything based on friends.

I asked Schlesinger, in writing, my thesis, should I mention this, you see, because I knew that, it was a red sensitive cell that he had tried, from what someone had said. Schlesinger said, "No, leave it out." Well, I left too much out. I could have, if I'd had enough sense, outlined what Stebbins had done in photo-electric photometry, without mentioning that particular thing. But I didn't mention Stebbins at all.

And this was a mistake which I deeply regretted. Stebbins wrote an article on the photo-electric cell in 1938, have you seen that? I can't remember where it's published.

DeVorkin:

I can certainly find it, no problem.

Hall:

Yes, in which he described the history, but didn't mention me (laughter).

DeVorkin:

That's too bad. (laughter)

Hall:

Which is all right. Then there was a symposium, 1940, June in Seattle. Stebbins ran it, and he invited me, Whitford, Kron, Huffer and Beals, and we each gave papers. It was the last (and probably the only) symposium on the photo-electric cell.

After this symposium, I traveled with Stebbins on the train from Seattle to San Francisco, and we got to be very good friends. Actually when he was ill and couldn't go to an IAU meeting — I think it was one in England at the University of Sussex — I got a card from him when I was there, saying he regretted not being there and that he hoped I was having a good- time and so on. He was ill at that time. So it all ended well. But I regret that it didn't begin well.

DeVorkin:

I'm at a slight loss now because I haven't read this material yet, but did you talk together with other people, with Stebbins, about the coming photo-multipliers?

Hall:

Yes, and you'll find it in the PASP summary of that meeting[2].

DeVorkin:

Good.

Hall:

Photomultipliers had been used by both Whitford and Kron. They built a guider for the 60-inch, which was used successfully at Madison and then taken to the GO-inch but it couldn't get down to faint enough stars. And I remember, I wrote a letter to A.L. Bennett, who was doing photo-electric work at Yale following me, on the faculty, and asked me what he knew about photo-multipliers. I don't know what he said. I can't remember it.

DeVorkin:

Which Bennett is this?

Hall:

This is A.L. Bennett. He left astronomy about the time of World War II. But he did an awful lot of observing. The weakness of his work was he simply didn't publish. I think he only published one paper in many years of work. Here is a photograph which I took — this was at the meeting in Seattle. And those five people represent about 75 percent of the photo-electric astronomy in the United States, or probably in the world, at that time.

DeVorkin:

You took this photograph?

Hall:

Yes, I took it. I had a cheap camera that you could plant, and then I ran, and I was making a face actually there. I was just getting my breath.

DeVorkin:

Yes, your hand is moving. You're on the left as I see it, then Whitford, Stebbins, Kron, and —

Hall:

— and Beals. Beals of course was the head of Canadian astronomy.

DeVorkin:

I would like to somehow be able to get a duplicate of this some time.

Hall:

All right.

DeVorkin:

This is quite a memorable photograph.

Hall:

I think it is, yes. I didn't show it yesterday. I had it, but I didn't want to go into this Stebbins business. There wasn't time. I do have something on that meeting. Here, this you might be interested in, one of the artifacts. That was the meeting at Columbia, where Green told me I couldn't be in the picture.

DeVorkin:

Also it gives all the names of the papers and things.

Hall:

Oh yes. And incidentally. rather interestingly, I think Adams gave a paper on the 200-inch telescope, which was not put in operation until 1949. But it was the first paper. I think. This was an invited talk. Is it titled there?

DeVorkin:

Let's see — "Large Telescope and Its Possibilities." Address of the retiring vice president for Section D. Walter Sydney Adams. That's right. Well, there were a lot of interesting things happening at that time. This was a very active year for Russell. Though you mentioned. this was a meeting he was not at? He didn't attend tbis one?

Hall:

The Yale meeting. He was not in the photograph, that's all. I didn't check whether he attended it or not.

DeVorkin:

Right. Here's a paper by Van de Kamp and others. That's a lovely picture of the Loomis.

Hall:

I have this in color, if you want to see it. A slide that Miss Barney gave me.

DeVorkin:

You took this picture?

Hall:

No. she did. Here's her color slide. I shoved that yesterday.

DeVorkin:

Oh, that's lovely. That's from the same direction.

Hall:

Same picture.

DeVorkin:

Same picture. I see. 1951. That's quite a tall tower. And so there was a sliding roof at the base?

Hall:

Yes, only the roof moved.

DeVorkin:

And that's where the 30 inch flat was. And that was equatorially mounted, followed the stars at half the rate?

Hall:

Yes, and actually, Schlesinger called it a ceolostat some time, but I think it was a siderostat because the field rotated.

DeVorkin:

Still it's quite a unique instrument. I'd like to ask you a question about your work in the early thirties. You mentioned that you did three color photometry of 347 stars.

Hall:

Yes. Those were all the stars in the Northern Hemisphere - brighter than 4.4 visual magnitude. This was a typical type of a Schlesinger program - he liked Durchuvsterungs.

DeVorkin:

This was a very early color system. What color system did you use?

Hall:

Well, actually, in those days, there were no sharp infrared filters. You couldn't buy interference filters, of course. They were not known. The filters I had were very broad in their response. Actually I used no filter at all in one case, and then one filter that cut off the yellow, then another filter that transmitted mostly the infra-red, they're listed there.

DeVorkin:

So your system was dependent upon what filters were available?

Hall:

That's right. They were Schott filters, the two that I used. Hertzsprung wrote me. We had quite a bit of correspondence, after he read my thesis, and he had suggested that I should have used a liquid filter, which I knew about. But I didn't think it practical. I had enough problems. You might be interested in Hertzsprung's letters?

DeVorkin:

Very much so.

Hall:

They were here yesterday, must be here now.

DeVorkin:

You mean you have them with you now?

Hall:

Yes, I had them with me yesterday. Here is a paper written when I was a graduate student.

DeVorkin:

Oh, good, I'd like to read this reference into the tape. "The Application of Photo-Electric Cells Sensitive in the Infra Red to Stellar Photometry," by John S. Hall, National Academy of Sciences PROCEEDINGS, Volume 18, No.5, page 365-367, May 1932.

Hall:

I think you know of those. This is the history of the observatory. (Hall has a number of reprints with him.)

DeVorkin:

Yes and then the biographical memoirs of Schlesinger and Brown, from the National Academy of Sciences. Yes, I know those.

Hall:

Here is the correspondence with Hertzsprung. There are several letters involved.

DeVorkin:

This is correspondence in the 1930's?

Hall:

My thesis wasn't published until 1934.

DeVorkin:

So this is all written from Leiden, this is 1934, I think we can go through the letters.

Hall:

Let me just show you the first one. Of course, I was very flattered to get a letter from Hertzsprung. I found that whenever he liked a thesis, he did this.

DeVorkin:

He would write to people?

Hall:

He'd write to the post doctoral astronomer.

DeVorkin:

That's nice. Did he suggest work for you to do?

Hall:

Oh yes. Actively.

DeVorkin:

Now I understand.

Hall:

Here is the first one.

DeVorkin:

You sent him the papers on photo-electric photometry and he's thanking you for them.

Hall:

I sent him the thesis.

DeVorkin:

The thesis. You worked on the Pleiades?

Hall:

Yes, that was for calibration purposes.

DeVorkin:

And color equivalents, and then

Hall:

Zeta Geminorum, that's a Cepheid variable.

DeVorkin:

And he's talking about calibrations, magnitude calibrations?

Hall:

Yes, he said I used the wrong magnitudes for calibration. This letter is a very useful sort of letter.

DeVorkin:

This is May 9, 1934. He includes this calibration curve, Lambda in microns. That's quite detailed. Three double spaced pages on both sides.

Hall:

Here are subsequent letters, afterwards.

DeVorkin:

I would like to be able to Xerox these, if it would be all right with you. But maybe we should talk about this more coherently. (Letters not copied during session).

Hall:

All right.

DeVorkin:

Do you have a large collection of letters? Have you kept all your letters from this period, with astronomers, through the years?

Hall:

Yes, but I don't know what would be of interest to you. I preserve things fairly well.

DeVorkin:

Yes, it's certainly evident that you have. These are in very fine shape.

Hall:

Here's a brochure of the eclipse of 1925.

DeVorkin:

Oh yes.

Hall:

Well, it's a simple thing.

DeVorkin:

What are these small pictures of instrumentation?

Hall:

Thatís mine. That's the Lindemann Electrometer, right here.

DeVorkin:

And you're looking at it?

Hall:

The photocell is here, and the light comes up from the bottom.

DeVorkin:

And this is the microscope that you needed to look at the electrometer.

Hall:

That's right. Schlesinger got this from the biology lab. He said it was a reject, but I think he stole it.

DeVorkin:

So it's a string electrometer?

Hall:

No, it's a quartz fiber electrometer, push pull thing, ten micron fibers, and they were gold plated, so that the electrons would go onto the fiber. And the plates were arranged in a push pull arrangement, so that the needle would cross the field.

DeVorkin:

I see. And here I see, in this larger scene, that your box is mounted on the top of the Loomis plate holder there, which moves in X and Y.

Hall:

That's right.

DeVorkin:

That's excellent. These excellent pictures. I certainly would like to obtain some copies of these.

Hall:

Well, I can see that you get some. I don't know what I have here. I have some things at home that you probably would be interested in — if I could find out what you're interested in?

DeVorkin:

OK, we can talk about that at the end. Let's find out how your career continued. After Yale, you went to Columbia, and this was directly with Schilt.

Hall:

Yes.

Actually, Eckert offered to hire me as an assistant in astronomy, and I was lucky to get any job at that tine.

DeVorkin:

Because of the Depression?

Hall:

Yes. I got $1000 a year for one year, and I was in the top floor of the Pupin Laboratory of Physics. The telescope was on the roof. My desk was in the N.E. corner of a loft area, which was half of the top floor. It was the southern half, and I had a desk there, and around me were various IBM machines, about six of them, which Eckert had had brought up from downtown. He was in direct contact with Thomas J. Watson, and he had a sorter, a collator, a multiplier. I think there were about six machines. He would take a pack of cards from one machine, and run them into the next machine, and so on, in sequence, to solve any particular problem.

DeVorkin:

Did you work with these at all?

Hall:

No. I continued my photo-electric work, using the refractor, the Rutherfurd Telescope, a very famous refractor. But I was working in the infra-red, and in the infra-red, the lights from the city were overwhelming. They were all incandescent in that day. Although I worked a good many nights, I had to throw the data away eventually, never published any of it. But at that time, I took courses.

I had a course under Rabi in statistical mechanics. And I took a course with Eckert which had to do with the reduction of Meridian circle observations, and astronometric problems in astronomy. I can tell you one interesting thing, though. One every Tuesday afternoon, I think it was, maybe Thursday afternoon, at an exact time, a young man came in from downtown, and went over to the other side of the loft, and visually examined large numbers of photographic plates that Schlit had obtained with the 6-inch at Mt. Wilson, studying variables in a globular cluster. And that young many was Jesse Greenstein.

DeVorkin:

And he was in New York City?

Hall:

Yes. This was before he went to graduate school.

DeVorkin:

And this work was entirely on his own?

Hall:

Yes. Schilt encouraged him, of course. But he was just interested in astronomy, and I think he probably wanted to get himself financially able to go to graduate school.

DeVorkin:

Yes, I see. Thatís fascinating. Did you have any direct contact with him?

Hall:

He sort of went in a straight line. As he came in, he would go right to the job, and then do what he wanted to do for that day, and then walk right out. Oh, we spoke to one another and so on, but we didnít discuss astronomy in any detail. He didnít discuss what he was getting, and I didnít discuss what I was trying to do.

DeVorkin:

But you certainly knew and remembered his presence there.

Hall:

Oh sure. It was a very pleasant relation, but no close contact, astronomically speaking.

DeVorkin:

Now, you stayed less than a year at Columbia.

Hall:

Well, I was there technically a year, but I was not there in the summer months. There were no students.

DeVorkin:

How did you obtain the position at Amherst after that, or did you go to Sproul?

Hall:

I went to Sproul, and toward the end of the spring of that year. I received a letter from J.A. Miller, saying that he had been impressed by what I was doing at Yale, when he came up to the quarterly meetings. I sometimes drove him to and from the railroad station in my Model A Ford.

DeVorkin:

This was the photo-electric work he was interested in?

Hall:

Yes.

And he had long wanted to start something like that at Sproul Observatory.

DeVorkin:

Miller was interested? I see.

Hall:

Yes, and he wanted to know if I would be interested in coming there. He offered me a salary of $1500 for one year. It so happened, I think, that he got this money from the American Philosophical Society and I believe he continued to get grants from the American Philosophical Society, on a one year basis. He was its Secretary.

DeVorkin:

That helps.

Hall:

So for three years I think I was on grants. He never discussed it with me, but I think that was the case. The fourth year, I think I was switched to Swarthmore finances.

DeVorkin:

This is very interesting to me, because it looks as though a good number of people were getting interested in photoelectric work, as a means for measuring brightnesses. They weren't repelled by this new technique?

Hall:

Photographic work was going downhill.

DeVorkin:

It was, even at that time?

Hall:

Because it was very difficult to measure extended objects photographically, and the polar sequence scale at the lower end where things were faint was very uncertain because then one ran into background effects. And that's where photography is very weak, compared to photo-electric work. Photo-electric work can sort them out precisely. You can't do it photographically.

DeVorkin:

Right. Were you really aware of these advantages even at that time?

Hall:

Oh, yes.

DeVorkin:

But yet you were still confined to bright stars at that time.

Hall:

I was confined by the telescopes mostly to bright stars. While at Sproul, Hertzsprung in a letter suggested that I calibrate my filters by making a coarse grating, and putting it over the objective. And in this way, I could get the energy distribution under the filters accurately. It was a very good idea. I misinterpreted it, and made a coarse grating, but it was 50 wires to the inch, and he has the idea of maybe ten wires strung across the whole thing.

So I got a dispersion with the Sproul Telescope of 500 angstroms per millimeter, and I made a gadget so that I could use both spectra, one on each side — the corresponding spectra — and shoveled the light into the multiplier. Also since the open and closed grating intervals were the same the even orders were missing and the IR could be measured. And so I vas observing spectra photometrically, and I was a pioneer in that.

DeVorkin:

That was the first spectrum scanner?

Hall:

In a sense mean, although it took me 15 minutes to scan. I mean, a screw arrangement, and I'd go from one wavelength to another. But the wavelengths were sharply defined, and that data is just as good today as when I took it. It's still fundamental data.

DeVorkin:

Yes. Let me turn the tape.

DeVorkin:

That's very interesting. Was that published?

Hall:

Oh yes. I published this material, and this is what I presented at Seattle at that meeting. I was observing bright stars, to be sure, but I was observing small sections of bright stars, and I was only getting 10 percent of the total light, and then dividing it up into ten more sections. I kept using the Lindemann Electrometer because I didn't want to stop to develop the use of an amplifying tube. One only gained a factor of about a magnitude using an amplifier tube. I instead used a power microscope, and was able to get enough stability so that I was not t a very great disadvantage, although at some, and certainly a disadvantage of convenience. See, Stebbins tried to use an amplifying tube in 1921 or '22.

DeVorkin:

Right.

Hall:

He called it an Audion tube. Thatís what he called it. You see, they were used in radio as audio amplifiers. Then he got Whitford interested in it, and Whitford, who was a physics student, did his graduate work doing that. He got the FP54 Plyotron, which was a very impressive name and a rather large tube for what it did.

DeVorkin:

That was the first vacuum tube amplifier?

Hall:

Yes, a very successful attempt of use amplifying tubes, instead of an electrometer. They used a galvanometer with it.

DeVorkin:

Right. During this period, did you maintain your contact with Prescott? Were you aware of other advances, or were there advances?

Hall:

Yes. I broke the special double-ended photocell he gave me, the first one. I hit the end of it with a screw driver, and he air went in. This happened at Columbia. It took me almost a year to get another good one. It was a photo-cell, a two element thing. I should have bought it today. I had it yesterday, and exhibited it. Actually I and one that Schlesinger gave to me.

DeVorkin:

Right, you mentioned that in the lecture. I certainly would appreciate just knowing that you have them and that they are in good shape.

Hall:

Yes, I thought youíd be interested in seeing them.

DeVorkin:

I would like to see a picture, or see it someday. When did you first become aware that photo-multipliers were coming onto the scene?

Hall:

At MIT Radiation Lab. Gerrry Kron had one. Stebbins tried to get some from Zworykin, and this was just at the beginning of World War II, but evidently he didnít get them. I donít know where Kron got his. You should have gotten that from Kron.

DeVorkin:

Yes, I have the information but its not exactly in my head right now.

Hall:

Yes. He said they looked very promising. He was testing it in his room, up at Cambridge, toward the end of the war. Then in 1946, he published what I think is a classic paper. It spelled the end, the death of photo-cells, and ushered in the modern day of photo-electric techniques. Of course, it could measure only a single area at that time. Now itís two dimensional.

DeVorkin:

Right. Were you aware at that time that Kron had had this lead?

Hall:

This interest?

DeVorkin:

No, that he had a technological lead, in that he had the photomultiplier during the war, and he had time to work on the circuitry. He basically had the jump on other people.

Hall:

Yes. Well, I sort of suspected it. I had started making photo-cells myself because I didn't know that photomultipliers would be developed during World War II.

DeVorkin:

When were you making the photo-cells?

Hall:

In Amherst, Prescott came up to Amherst and gave me advice on how to do it. And I was up [to] a production of one photocell per day, when I left to go to MIT. I had a very bright young student who helped me, and he stayed at Amherst and actually did his honors work under my long range direction when I was at MIT, building a device so I could quantitatively bake the photo-electric cells and seriously control this critical part of the operation.

DeVorkin:

Who was the student?

Hall:

Harold Ewen. Yes.

DeVorkin:

Harold Ewen of Ewen and Purcell?

Hall:

Yes. A man who made a horrible mistake by not going on in astronomy, or physics. I can tell you his background, if you're interested. It's a rather nice background in a sense. I mean I can tell you why this all happened. When I vas at Amherst, at the observatory, in about 1938 and '39 Even's father, who was a teacher in a high school in Springfield, visited the observatory one day, and said that whatever Harold did, he wanted him to make money, and that he strongly advised him to get a degree in law, because then he could protect his patent rights.

He said he didn't want Harold living the life that he lived, on a very low salary, teaching in high school or college or something of this sort. And so Harold did study patent law, in addition to getting his PhD in physics at Harvard. While at Harvard he got surplus radar equipment, and tuned it to the frequency of the hydrogen line. And when he was ready to try it, he asked me, "Where shall I point it? To what what [sic] declination?" See, he couldn't set it in hour angle.

He didn't have any way to guide. "What declination? And when should I try to observe, so that I have the greatest probability of detecting neutral hydrogen?" I foolishly said, "Well, Orion is full of hydrogen. It's ionized, but there must be some neutral hydrogen." So he did. He detected it, but it wasn't the best region by any means. It was a rather poor one, certainly.

DeVorkin:

This is post-World War II?

Hall:

Yes. And he beat the Dutch by three months. Purcell advised him and chose the problem, and helped him all along. Purcell was a very bright man, and he eventually received a Nobel Prize of course.

DeVorkin:

That was the limit of your contact then with Ewen?

Hall:

Yes. I saw him once or twice since then. I guess he's a very successful businessman. I always thought it was a crime that he didn't stay in science. I tried to persuade him to stay on, because he could have been a leader in science almost at once.

DeVorkin:

Well, weíve pretty much gone through the thirties, and we have an idea of what you were developing. You were continuing to work on photo-cells, in contract with Prescott. How did you go to Amherst after Sproul?

Hall:

In my third year at Sproul it became evident that Miller was resigning as director, and they were about to choose a new director. Stebbins came, and looked the place over, and left. Van de Ramp came, and Van de Ramp was chosen as director. So I could see that the emphasis was going to be on astronomy, and Green was very anxious for me to come back to Amherst. He persuaded the president to offer me a job, and so I went.

DeVorkin:

That makes sense. You were married while you were at Sproul?

Hall:

That's correct.

DeVorkin:

1935.

Hall:

That's right.

DeVorkin:

How did you meet your wife?

Hall:

Here in New Haven. She taught at the Foote School.

DeVorkin:

Oh, at the Foote School.

Hall:

Have you heard of the Foote School?

DeVorkin:

Yes.

Hall:

She graduated from Wheelok, and the first year, right in the depths of the Depression, she got a position at Grosse Point, Michigan, and taught in the school where Doty Ford was a student, a little girl. I think she was in her class. She taught second grade or something.

DeVorkin:

You met her there?

Hall:

Yes.

DeVorkin:

Yet she stayed here while you went down to Sproul?

Hall:

That's correct. And when I was at Columbia, she used to come down to see me; I had no money to come up here. Hardly enough to take her to the movies.

DeVorkin:

But you felt a certain amount of financial stability by 1935, to get married, is that what the issue was?

Hall:

Yes. I think that's the issue.

DeVorkin:

Moving on to Amherst, you continued to work on your photo-cell work.

Hall:

Yes, I was still doing the differential spectral photometry, using the 18-inch, and fortunately made up for the fact that I went from a 24 to an 18-inch telescope, because R.M. Wood was making blazed transmission gratings. I went down to see him on two or three occasions, and he very kindly made up quite a number of them for me. He made up split gratings, to match my device for channeling both first orders into the photo-cell could be improved. He never charged me a cent for this work - the idea probably never crossed his mind.

DeVorkin:

So that whole technique was based on a misinterpretation of Hertzsprung's letter?

Hall:

A Hertzsprung letter. Yes.

DeVorkin:

That's really neat. I see.

Hall:

But this is the way things happen in science, you know. I mean, it's either serendipity, or misunderstanding. Schlesinger had such a story about Bailey down in Chile.

DeVorkin:

Solon Bailey?

Hall:

A new comet was discovered, and Harvard sent him a telegram, and there was an error in the telegram of three hours in right ascension, and Bailey found a comet. But he had found another comet, at that erroneous position. If that isn't serendipity, I don't know what it is.

DeVorkin:

That's marvelous. I never heard that story. Well, World War II was certainly starting, and you were aware of it.

Hall:

Oh yes.

DeVorkin:

Were you also aware that there were many practical applications of photo-electric cells, and its development, not only in industry but in the military, for sensing devices? Did any of this have any bearing on your continued research, before the war?

Hall:

No. Let's see, there was a company that was making shampoo or something for the treatment of hair. They wanted to measure the color of hair, and actually I spent quite a bit of time, and they never gave me a cent or even thanks for it.

DeVorkin:

Do you know the name of the company, remember it?

Hall:

No, I can't remember it now.

DeVorkin:

It was in the Amherst area?

Hall:

In Springfield. Prior to that, the only thing that I got involved in was when I was at Swarthmore, at Sproul, a man was interested in whether fog lights would be useful. That is, can one use a different color to penetrate fog better? And so I took my equipment off the telescope, drove up to Cape Cod and spent two weeks there, waiting for fog, to measure the transmission of light through fog, and found there was no effect of color.

Later on, I learned that the droplets were about 10 microns large, and therefore they were just blanketing all visible rays. But at that time, fog lights came out, that you put down below your regular headlights, and they had lenses on them that were spiral, had a spiral on them.

DeVorkin:

Fresnell?

Hall:

No, they were not Fresnell, it was just the way the glass was made, for sales. And we sat down and tried to figure out why, and somebody came up with the answer that, the light screwed its way through the fog. (Laughter) Anyway, that was the only experience of practical use, that I had.

DeVorkin:

Well, you did spend the war years at the Radiation Lab. Could you discuss how you ended up there? And what your feeling was about participation in the war?

Hall:

I'd learned that World War I could have been avoided; that it was an economic war. But World War II I felt was a war which had been brought on by a fanatic, and that we'd better defend ourselves, and I had a feeling that everyone there felt the same way.

DeVorkin:

At the Radiation Lab?

Hall:

Yes. It was a matter of whether you wanted to do what you pleased the rest of your life or wanted to be a slave.

DeVorkin:

Now, who were you in contact with that brought you to the Radiation Lab?

Hall:

Well, my professor of physics, Ted Soller, was there. Theodore Soller. He taught the course in optics at Amherst. Later, when he retired, I persuaded him to come to Flagstaff. He's living there now. And I hired him at Lowell Observatory. Because he could take a problem and solve it from A to Z. You never had to worry about it, as long as he understood what you wanted.

And he worked at Lowell for several years. Now, he's traveling, enjoying himself. Anyway, Ted Soller was there, and also Gerry Kron, and I think between the two of them, they got together and decided that why should they be at MIT when I was out free doing what I pleased? And so, Loomis, the head of personnel wrote a letter to me and to the president of the college and so on.

DeVorkin:

Did your family move to Cambridge with you?

Hall:

Yes. We lived in three different places in Belmont, the third place, was interesting because nobody would take it. It was an empty house. Supposedly it had ghosts and this sort of thing. Anyway I persuaded the owner to let me fix it up and live in it, and it vas the nicest place we lived in. It was a beautiful house, in a sense. It had been mistreated horribly. Without too much work, we made it quite comfortable.

DeVorkin:

What were your specific duties at the Radiation Lab?

Hall:

I started in Ernie Pollard's group, which was the systems group, meaning that we shopped around the laboratory, trying to assemble parts to put together a complete radar system. And then, later on together with R. Meagher, I was made a group leader. I think he went to Illinois. Loomis knew him very well, Loomis was from Illinois. Each was a physicist. I had just one real job, and that was to work on a superdupersystem for aircraft carriers. one which could detect enemy planes at night.

DeVorkin:

So this was all in radar work.

Hall:

Radar, yes.

DeVorkin:

You did no photoelectric work?

Hall:

Oh no. Astronomy was completely out.

DeVorkin:

What part of your training, then? It was as a physicist of some sort.

Hall:

Yes, it had basic physics, and really, the physicists ran the Radiation Laboratory. The Engineers were considered very important, but incidental as far as leadership was concerned. It was a rather interesting situation, I thought. I mean, DuBridge was director, and his staff of about ten division heads, with one exception, were physicists. Rabi was one of them. Ivan Getting was another.

DeVorkin:

Who was the one exception?

Hall:

Hubbard. He was in charge of a division that had to do with motors servos and things of this sort.

DeVorkin:

He was not an astronomer.

Hall:

No, he was an engineer.

DeVorkin:

You mentioned Kron was there.

Hall:

He wasn't there the whole time, but up to the last year.

DeVorkin:

Right. But were you in direct contact with other astronomers? Who were working there?

Hall:

Well, I knew Kron, and Mayall was there, if I remember correctly. They're the only ones I can remember at the moment. Miss Lincoln a solar astronomer.

DeVorkin:

I know that there were others there. The names escape me too. Certainly the Harvard astronomers were around.

Hall:

They were not at MIT. They were in other groups there at Cambridge.

DeVorkin:

Were you aware of what other people were doing? I'm specifically interested in what astronomers were up to, in the war effort.

Hall:

Well, of course, Bowen was very much in it.

DeVorkin:

Yes.

Hall:

Let's see, Whitford was in it. There weren't many astronomers in the thirties, compared to now. I mean, astronomy blossomed after World War II, when government help came in.

DeVorkin:

Right. You mentioned a very early contact with Alan Waterman that I want to follow up. You had no contact with Waterman during the war?

Hall:

No. I saw him after the war. I was in Washington at the Naval Observatory.

DeVorkin:

Let's get to that in a moment. Can we have a few more minutes?

Hall:

Oh sure.

DeVorkin:

What were your specific technical duties then at the Radiation Lab?

Hall:

It was eventually liaison between the Lab and GE. General Electric was putting together this system for carriers, the first one, which was a 22 million dollar radar, and the question was not money but time. And so the whole philosophy was quite different from anything I'd ever come up against in my life, where time was the only important thing.

And I had quite a bit to do with the engineering staff at GE and at Bridgeport here trying to feed scientific information which they could engineer from the MIT to them. I was involved with three successive systems - one of these for smaller carriers. So, it was a matter of getting the information from individuals, and feeding it to GE, or having meetings in which I could get the engineers and the individuals together, if it seemed necessary. Some things were too complex for me to act as a medium. I mean, it should be left to direct contact.

DeVorkin:

This is a very difficult position to be in. You need to know what is being done, what are the advances, but you also have to know how to translate them into industrial production terms. Why do you think you were selected for this?

Hall:

I don't know. Actually I was reasonably successful because the laboratory was about to embark on a flying radar system that would detect planes, and be a command post really. And I was asked to be in charge of that. But it turned out that I couldn't do it, because I had this other project on my mind completely, and it was quite a different project, in a sense. You didn't worry about things being light. You didn't worry about 400 cycles and so on.

DeVorkin:

This was for a battleship?

Hall:

Yes. Mine was for aircraft carriers.

DeVorkin:

The aircraft carrier, right.

Hall:

And so Ernie Pollard said that I was just a one project man, and that I shouldn't continue. I was only in it a couple of weeks, and he could see that I couldn't do it.

DeVorkin:

The aircraft problem?

Hall:

Yes. He got someone else. I stayed with the ship business. Actually I went from Boston down to Norfolk on a carrier, when they were trying out the first big one that was made by GE. It was a 5000 pound antenna on the highest mast, 140 feet above the ocean, and we had some rather interesting experiences. Going down. we were to turn the set on in the morning, which we did. And our A Scope, which had intensities as a function of range, showed a lot of spikes coming up at equal intervals, all along it.

This we'd never seen before, so we decided there was something wrong in the ranging circuit. We had a spare ranging circuit, so we put that in and got exactly the same thing, and gee, we were horribly upset, until we saw the first ship come over the horizon, and it was the first of a line of Liberty Ships going to North Africa for the invasion, and we were getting unusual refraction and looking over the horizon at each ship. It was a fantastic coincidence.

DeVorkin:

Your role in the ship was technical in any way, or still managerial?

Hall:

Well, just seeing that everything worked. I was supposed to try and make things work, between the ship's personnel and our personnel. I knew how to run the system, and was in charge of saying what should be done next, if there were troubles. We had a test station down at Jamestown, Rhode Island. And early in the game the Navy made us run a three week test. They figured that since there were 800 tubes in the system (there were a lot of remotes), some of these tubes would be going out.

So we had the three weeks continuous test, and one night, the man on duty, from MIT, was told that the signal was lost. So he jumped out of bed and went downstairs. And as he vas going by one of the chassis, he saw that a tube wasn't lit, And he immediately replaced it, and they were off the air only three minutes. But they were off the air half a day because of mechanical problems. And this sort of proved to the navy that they must not fear the electronics so much as the mechanical problem.

DeVorkin:

That's a good lesson. Yes. During this time, did you do any astronomy, while you were at the Radiation Lab?

Hall:

None whatever.

DeVorkin:

Yet, within a year after you returned, after '46, you had begun working on polarization. Is this correct?

Hall:

Yes, because there was a man there in the receiver group who had developed a synchronous amplifier, whereby you could rotate everything which generated a sine wave and rectify it and get the DC current out, and he was the same man at Princeton who has been talking about the shape of the sun.

DeVorkin:

R.H. Dicke (RSI 17 268, 1946)

Hall:

Yes, Dicke. And I got the circuit, and took it back and built it and tried it, and it worked. I figured that polarization would be one of the most interesting things to look for. And it was when Chandrasekhar had said that one should look for polarization eclipsing binaries. And then W. Hiltner and I went to McDonald in the summer of '47 or '48, Ď47, I think, and we did detect polarization but it didn't seem to change as the eclipsing binary changed, and Hiltner said, "Let's publish something on it.

I said, "I'd rather we made some more observations." I made observations in the winter and Hiltner had too. Then the following spring, I heard that he was publishing a paper in SCIENCE independently of me, which upset me. And so I quick wrote a paper on what I was doing, and sent it to SCIENCE. So SCIENCE got the two papers about the same time, and Struve, Shapley and maybe others were sent the papers. The editor asked them what to do about it. And I think they recommended that we get together and publish a joint paper.

DeVorkin:

What was your relationship with Hiltner in the beginning? You were at Amherst.

Hall:

Yes.

DeVorkin:

Was he a student or faculty member there?

Hall:

No. But he was interested in this same problem. I donít remember how we happened to get together.

DeVorkin:

He was at Yerkes at that time.

Hall:

Yes. And unfortunately I had a very had case of mumps at the critical moment when my wife received a call from the AAAS, suggesting we combine our papers, and I just couldn't do anything. And so they were published separately, which I regret. The last time I say Struve at an Astronomical Society meeting, he took me aside, and said he had something to tell Me. He wanted me to understand that Hiltner was in his opinion not at all to blame for the difficulties we had had, the misunderstanding. Hiltner was under strong influence of someone else, at that time. So Hiltner and I have been good friends since '23

Hall:

Yes. But Struve was extremely fair about the whole thing, and I know Shapley had his fingers in it. Well, I suppose I should mention that Chandrasekhar was the other person. My only reason why I think that he would have been biased in any way was because he wanted it to be a completely Yerkes project.

DeVorkin:

Well, that's quite a common feeling and I can understand that.

Hall:

Yes. But Struve was extremely fair about the whole thing, and I know Shapley had his fingers in it.

DeVorkin:

Is that possibly how the contact was made, between you and Hiltner?

Hall:

I'd have to look it up. I've taken all the correspondence, and it was in the Memorabilia Room at Amherst College but now probably in its Frost Library.

DeVorkin:

Oh, so, you've deposited your papers there?

Hall:

Yes, all the correspondence and some of the data on this particular subject; the discovery of interstellar polarization.

DeVorkin:

I see. Approximately how many letter are deposited there?

Hall:

I would say ten or something of this sort, some of them from Struve, some from Hiltner.

DeVorkin:

So would we contact the archivist there?

Hall:

Yes. I don't know just where that Memorabilia Room is now. I can find out when I'm up there.

DeVorkin:

Do you still have copies of these?

Hall:

I have copies, but I put things in a coherent form there. The copies I have may not be complete and. they're not sorted.

DeVorkin:

Well, we're almost out of time. Do you feel that we have produced a reasonable overview of your development of interests and techniques in photoelectric photometry, up to the end of World War II, at least?

Hall:

Yes, I think so. After the war I went to the Naval Observatory, and got heavily involved in the image tube business.

DeVorkin:

You were on the Carnegie Image Tube Committee, later on.

Hall:

Yes, actually I'm chairman of that committee. Tuve never wanted to disband it. He did want me to remain as chairman. It's a purely ghost committee. It has no meetings. Kent Ford really carried the ball after the first two on the whole thing.

DeVorkin:

Why didn't you remain at Amherst? Was it the chance of moving to a bigger observatory?

Hall:

Yes. And I thought that I could use that 40-inch telescope.

DeVorkin:

The Ritchey-Cretien?

Hall:

Yes. Schlesinger had often spoken of that telescope, and what a shame it was that it was in the city of Washington. He had recognized its value. It was the only Ritchey-Cretien telescope, other than a small 20-inch in France, in existence. And he felt it should be given its trial. Schlesinger had tremendous respect for Ritchey, and actually, when that telescope was moved to Arizona, and Pat Roemer started making pictures of comets and so on, it became the model for most large telescopes in the United States, or variations of it. Cretien came, and told me how he told Ritchey about the new design — if he just turned down the secondary a little, he'd get rid of the coma. He just happened to be at Mt. Wilson, when Ritchey was figuring the telescope. Evidently, Schwarzschild, the elder Schwarzschild (Karl) had built the equivalent of the Ritchey-Cretien in lenses.

DeVorkin:

I'm familiar with that design.

Hall:

You are?

DeVorkin:

Yes, there was a small Schwarzschild where I was an undergraduate at UCLA.

Hall:

Has that so?

DeVorkin:

A camera, yes.

Hall:

That's interesting.

DeVorkin:

I didnít like to use it much. But that's interesting. One final thing about your war effort. You were the editor of RADAR AIDS TO NAVIGATION in 1947.

Hall:

Yes.

DeVorkin:

Do you have a copy of that?

Hall:

Oh yes.

DeVorkin:

Is it a very large report?

Hall:

It's a book. It's one of the MIT series, of which there are was about 15 or 20. It was No.3.

DeVorkin:

That would be an interesting book for me to find in the library.

Hall:

I think you can find it in most libraries.

DeVorkin:

This pretty much identifies what your work was, and what your team's work was?

Hall:

No, it doesn't at all, really. It's really a navigational book, and how radar can be used in navigation. Actually the radar I was interested in was never used for that purpose.

DeVorkin:

I see. What is that?

Hall:

Well, it vas a height finder, and as I say the radar went on top of an aircraft carrier. The purpose of it was to direct the fighter planes at night, to attacking enemy planes.

DeVorkin:

So then this was one of the earliest studies showing that navigation could be aided by radar?

Hall:

Yes. And also in the main the important part of the book, I think, has to do with air traffic control.

DeVorkin:

And this was the original statement on the subject, do you know?

Hall:

Well, one of them. I donít really. I havenít looked at it for many, many years. I donít know how close it is to the present systems.

DeVorkin:

Well, our time is up. Thank you very much.

Hall:

Thank you for the chance of talking to you.

[1]Tape deposited at AIP.

[2]PASP 52 (1940) pg. 257.