Oral History Transcript — Dr. Adriaan Wesselink
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Interview with Dr. Adriaan Wesselink
Adriaan Wesselink; June 21, 1978
ABSTRACT: Early life and family interests in Holland; study at the Rijksuniversiteit te Utrecht; courses in mathematics, physics and astronomy; move to Rijksuniversiteit te Leiden in 1929 and contact with Ejnar Hertzsprung; work for Hertzsprung on variable stars; Hertzsprung's career; Jan Oort's lectures on galactic rotation; recollections of Willem de Sitter; Leiden in the 1930s; Paul Ehrenfest's colloquium series; continued research with Hertzsprung during the 1930s; contact with Gerard Kuiper; research on Delta Cephei, dynamical parallaxes, and energy distributions in stellar spectra; Leiden Ph.D. thesis, 1938; stellar pulsations; Lodewijk Woltjer; year at Yerkes Observatory, 1938-1939; relations with Kuiper; recollections of staff research at Yerkes; South Africa, 1939; recollections of Marcel Minnaert. Short discussion of Jacobus C. Kapteyn, including plans and execution of 1936 eclipse expedition to Russia; war years in Holland; Dutch astronomy in World War II; living conditions; postwar move to South Africa and various positions there; move to Yale University in 1964. Also prominently mentioned are: Edwin Eugene Aldrin, Nikolai Pavlovich Barabashov, Bart Jan Bok, Dirk Brouwer, Subrahmanyan Chandrasekhar, Christie, Pierre Demarque, Arthur Stanley Eddington, Albert Einstein, Louis Henyey, Edwin Powell Hubble, Ivan Robert King, Hendrik Anthony Kramers, Bertil Lindblad, Edward Arthur Milne, A. Nijland, L. S. Ornstein, Henry Norris Russell, Karl Schwarzschild, Martin Schwarzschild, Otto Struve, Thackeray, Hendrik Christoffell van de Hulst; Bethany Observatory, Finsen Radiation Institute, Leiden Southern Station, and Radcliffe Observatory.
TranscriptSession I | Session II
DeVorkinThis is a follow-up interview with Dr. Wesselink on June 21, the summer solstice, 1978, at his home in Bethany. We were talking a little bit about J.C. Kapteyn and your opinions about him.
Wesselink:Yes. Well, of course I never knew Kapteyn in the first place. What I know is from books written about him, and what I hear from people who have known him. The people who I have known who were students of Kapteyn all are glowing and enthusiastic about Kapteyn's teaching. Apparently he had a knack of making people love astronomy; even people from other fields like mathematics were drawn towards astronomy. They wanted to follow Kapteyn in all his new ventures in statistical astronomy. One person of this nature was W. de Sitter. He was a mathematical student in Groningen and went to Kapetyn's lectures and was so taken by them that he became an astronomer although not particularly in the same field as Kapteyn's work himself. W. De Sitter, as you may know, was in dynamical astronomy, celestial mechanics and astronomical constants. Nevertheless he became famous in relativity theory and the expansion of the universe later. But anyway he got his first contact with astronomy through Kapteyn. Van Maanen was a Kapteyn student, I think. And Klein Wassink, and P.S. van Rhijn were too. Van Rhijn succeeded Kapteyn at Groningen as professor. I don't think B. Bok ever knew Kapteyn.
Wesselink:But P. van de Kamp knew him, I think, and the most famous one is J. Oort. Oort followed Kapteyn's lectures in Groningen for about two years only, I think, because Kapteyn must have been already very very old when Oort first sat in on his lectures.
DeVorkinWas Jan Schilt with Kapteyn?
Wesselink:Yes, Jan Schilt was also a Kapteyn student. You may ask him for more particulars. He's still alive. I don't know what his condition is.
DeVorkinHe's in Leonia, New Jersey, very close to Philadelphia. I believe Dr. van de Kamp is still in contact with him.
Wesselink:Did he move?
DeVorkinFrom New York, yes.
Wesselink:He lived in Providence, didn't he? Because Clemence lived quite close to him in Providence.
DeVorkinI'll try to check. Well, we were having a very interesting discussion about your feelings about Kapteyn's role in the development of astronomy.
Wesselink:Well, I mean, you put me straight there. Kapteyn's role in astronomy is primarily his influence on others, in my opinion. He was able to make them enthusiastic about astronomy, and these others I think did a lot of work in astronomy. What Kapteyn did was all very sound and solid. For instance, he certainly started statistical astronomy as a new branch of astronomy. Not every astronomer is able to start a new field. Even so, everyone knows that the successes of Kapteyn in the structure of the universe were not all that remarkable. Maybe it couldn't be done any better. But the universe as it looks now is entirely different from how Kapteyn saw it. Nevertheless, the methods Kapteyn initiated are still being used and were used by people like Oort and van Rhijn and Bok, all the successors to Kapteyn. So he started quite a ball rolling, that's no question. And his CAPE PHOTOGRAPHIC DURCHMUSTERUNG of course is the standard work being used by astronomers all over the world even today.
DeVorkinLet's move on then to the point where we left off, which was just at the Yerkes years. We'd finished discussing your seven months or so at Yerkes in the late thirties. Would you like to go back and talk about the eclipse expedition? It appears to be a very interesting one. This was in 1936?
Wesselink:Yes, in 1936. There was a total eclipse of the sun visible in Russia, in Siberia, and in Japan. The line of totality went over all these countries, so it was touching Russia near the Black Sea in the early hours of the morning, and three Leiden students -- I was one of them --
DeVorkinYou were still considered a student in 1936?
Wesselink:-- I didn't have my PhD yet. We were assistants in astronomy of the observatory and we talked this over, and thought it would be very nice to go to Russia for the solar eclipse and do some work on it, although we were not clear what to do. We just were I think fairly adventurous, and thought this was a beautiful occasion to go to a foreign country. And so we contacted the well-known solar physicist in Holland, Minnaert, and we told him about our plans and asked him if he had scientific program for us that we could do there. We had still half a year's time for preparations. Minnaert said at once that he did have something in mind. He said, "It would be wonderful if you could measure the limb darkening at the edge, at the very edge of the sun, because that's something you can hardly measure without a solar eclipse because of the turbulence in our own earth1y atmosphere." The intensity of the extreme limb is so low that the turbulence in our atmosphere, by affecting the seeing, causes to blur the limb, and therefore the measures of the limb darkening at the extreme limb are somewhat unreliable. But at a solar eclipse, a total eclipse of the sun, you could measure the total brightness of the crescents as it gets smaller and smaller, just before second contact, and from that function -- the drop off of the total intensity of the crescent -- one should be able in principle at least to derive the limb darkening. Of course, you have the third contact where the brightness is increasing again, after totality, the crescent is coming up again, and that is the same thing repeated all over. So we thought this was a beautiful program, although we didn't have the faintest idea how to attack this technically. So we went back to Leiden from Utrecht, where Minnaert was a professor, and sat thinking about how we could execute Minnaert's ideas and program. It was then that, after a few weeks, it occurred to me to invent the method that we actually used at the eclipse. That means I took a board with small mirrors on that board, all convex. They were really made from aluminized eye glasses, of the proper curvature. You pointed that board with all the mirrors on it, to the sun. All the mirrors show a reflected image of the sun, which is of course rather much smaller than the actual image of the sun, in minutes of arc. And the brightness of the sun in all these mirrors differs according to the curvature of the front surface. Then we used movie cameras to photograph these mirrors, and we had them very far out of focus so that all the images were the same size but the surface brightness of the images was different. So we were able in that way, with one exposure time, (the movie cameras could only move with one particular rate, and therefore the exposure time was constant) to produce a contrast curve of an intensity ratio of 1000. But the mirrors were invented to prevent over and under-exposure.
DeVorkinThey caught a large range of intensity.
Wesselink:That gave me a range of intensities. On the processed film the images belonging to sorne of the mirrors were over-exposed, whereas on others it was under-exposed. But there were also some mirrors which were rightly exposed. That was enough, because you could always tell which mirror that was. So it was done. The mirrors were photographed during the eclipse, just before the totality and just after, and the intensities therefore of the total and of the crescent, were measured. The time of course was also recorded for every picture. There were 16 exposures per second. And the whole eclipse curve was obtained that way. Very unfortunately, there were some clouds about, and therefore, I think the results were not nearly so important as they would have been in good weather.
DeVorkinYou realized of course the clouds were there immediately. You didn't know immediately that this data would still he useful. How did you feel about that?
Wesselink:Well, we thought that the clouds had done a lot of damage. We realized that immediately. But we had some hope that it would give some interesting information with regard to color. We did this with two movie cameras loaded with different film, and we had different filters in front of the cameras, so that we could also obtain the march of the colors of that extreme crescent. We found that the color didn't change during the 100 seconds that the cameras operated. The color didn't change much. Which was an interesting find.
DeVorkinYes. I would expect that the color would change because you're looking at different levels into the atmosphere and different temperatures.
DeVorkinWhat was the reasoning behind that? Better limb darkening of law?
Wesselink:Well, I think that Minnaert was very startled with that result, in the first place. But later on he told me he wasn't. He thought this is just as it has to be, because the intensity at the extreme limb should go down to zero, he said. And if they both go down to zero, then the ratio in intensity shouldn't change that much. But first he was not thinking of it going down to zero, you see. And there was quite an argument between me and him about why the intensity at the solar limb was not zero, in his opinion. But let's not go into that.
Wesselink:Well, because I asked him where he would put the solar limb in the first place. I said, "It's all a matter of definition, see. I put the solar limb there where the intensity is zero, so the intensity at the limb can't be anything else than zero at the limb, because you define the limb as the position where the intensity is zero."
DeVorkinAnd what did he say?
Wesselink:He puts it where the density in the atmosphere is zero. But that's something you cannot find out.
Wesselink:So for all practical purposes, the solar limb is there where the intensity is zero, you see. It's a philosophical question, which you never can get around, but it was rather interesting at that time that we quarreled about it so much.
DeVorkinDid you quarrel about it in the literature?
Wesselink:Personally, rather. I said that he would never be able to get around this problem.
DeVorkinHow often did you see him? He was at Utrecht?
Wesselink:Well, he was at Utrecht and I saw him once every three months I think. Later on, I was called in on the Eclipse Commission of' the Netherlands to handle the solar eclipse of 1940. This of course was to be in South Africa.
DeVorkinDid you actually go down there?
Wesselink:I never went there because of the war. The war intervened, and although I had made all my preparations for the expedition -- I had a new set of mirrors, better than the older one, and everything was much better organized -- because of the invasion of the Germans in May, '40, I never could get out of the country anymore, and this whole thing had to be forgotten.
DeVorkinDid anyone pick up the technique later on?
Wesselink:Nobody ever repeated that technique since.
DeVorkinLet me ask you something about your experiences during the expedition. You noted that you went through the Caucasus and then to this city...
DeVorkin60 kilometers north of Maikon. What were your experiences? You also met a Russian expedition that was quite important in your work, also a French expedition.
Wesselink:Yes. That's right. (Pause to examine notebooks taken during journey)
DeVorkinThese are little red notebooks or diaries that you took on the expedition?
Wesselink:Yes. Here is a Russian stamp that means it has been inspected at the border and was considered not dangerous for the Russian government.
DeVorkinI see in one of the books a small sketch of a sailboat. Are these your general impressions and diaries?
Wesselink:Yes. Those are my impressions and diary which I made on my travels.
DeVorkinWhat are the basic things that you recorded in here?
Wesselink:Well, what I recorded in here was not very scientific. It was usually my encounters with the people there, and our adventures, before the eclipse, during the eclipse and after.
DeVorkinI'd be most interested in your scientific observations, primarily your contact with the Russians. I understand there was a Russian expedition led by Gerasimovic?
Wesselink:Yes, Gerasimovic was the head of the whole Russian venture throughout Russia. I never saw Gerasimovic, but I saw Professor Barabeshev, I think, that's how they spell it. He was there, and he was a very friendly man and helped us quite a bit to get settled there at the airport. We were at the airport of Beloretschins Kaya where we had our camp. I have forgotten what actually was his project. I don't know that anymore. Well, we had other experiences. On the day of the eclipse, we discovered a nova. It was Nova Lacertae, which is now in the literature. On the 19th of June, 1936, in the evening, I discovered it, not without the help of Uitterdijk. Without Uitterdijk I may not have found it. But I always look up in that area of the sky, where Delta Cephei is. I like to see whether it is bright or faint. I still do that. Just out of interest.
DeVorkinThat's a famous star.
Wesselink:Yes. And I couldn't find it that evening, and I thought: "Well, the eclipse must have had some kind of devastating effect on me in the morning, but I cannot find Delta Cephei tonight in Russia, what happened?'' So Uitterdijk looked up, he knew the area, and he said, "I can't. There's something happened in the sky. There's something different. I mean, it looks all different.'' We had a map star with us, and he got it out, and soon found that there was an extra bright star which normally doesn't belong there, and that was a nova. So we were delighted finding a nova, and phoned Barabashev, the Russian leader in the Russian camp, and asked whether they knew about it. He said at once that he knew about it -- that he got a telegram from Copenhagen the day before the eclipse, telling him about the discovery of that nova. So the discovery was not ours, because we were not the first, but anyway we were proud that we had seen it.
DeVorkin:How did you travel, usually by train?
Wesselink:We traveled by train and sometimes by car. We went by car right through the Caucasus from Ordzonikidze to (Tiflis).
DeVorkinYou started from Warsaw and Kiev. These are the cities that you indicated in the paper in the BAN in 1940.
DeVorkinNow, when did you realize that this was going to be valuable data after all? When you got back to Leiden?
Wesselink:Yes. I at once examined the film at Leiden. It took me some while because there were 6000 cinema pictures to examine with an eye piece. But I realized very soon that the clouds had had a very had effect on the result. But even so, people thought this method was important enough to try it again in 1940.
DeVorkinWho thought that?
Wesselink:Minnaert thought that. Minnaert thought it was important, and the eclipse committee of the Netherlands including van der Bildt and Moll. He was professor in experimental physics in Utrecht who was famous for the invention of the Moll microphotometer.
DeVorkinYes. I didn't realize he was interested in the sun.
Wesselink:He was interested in this method of getting this result.
DeVorkinYes, it's an interesting technique of sensitometry. It tremendously broadens your range.
Wesselink:Yes. And there was also the advantage that you didn't have to try it on an actually eclipsed sun. You knew that the sensitivity was always correct of your apparatus, because you would always catch some of the mirrors at the right intensity.
DeVorkinYes. What was the actual intensity range? What was the machine capable of recording, intensity range?
Wesselink:Well, it was calculated from the curvature of the mirrors. You could calculate the intensity.
DeVorkinSeveral thousand, wasn't it?
DeVorkinWell, I understand that you had 6000 cinema frames but on each frame you had many images. You had over 30,000 images to measure?
Wesselink:No, because most of the images couldn't be measured. They were either under exposed or over exposed. So you had to measure only two or three on every frame.
DeVorkinAnd how did you divide up the work?
Wesselink:I did it all myself.
Wesselink:The results looked fine from eye estimates. I made the eye estimates first, and that was enough to establish that it worked beautifully. And then they were measured in the microphotometer, which took a long time. Took months at least. That was divided between the three participants of the expedition, and myself.
DeVorkinAnd you had discussions every so often with Minnaert?
DeVorkinDo you feel that the data that came out was a significant advance in our understanding of the limb darkening of the sun?
Wesselink:No. I don't think so. Not yet -- because of the clouds.
DeVorkinDo you feel that this should be repeated in the future?
Wesselink:Well, I just inquired about it recently to de Jager, who is Minnaert's successor. Because nowadays of course we have satellites and astronomical telescopes in space, and they are not hampered by seeing conditions in the atmosphere. So I inquired of him if it would be a useful project for one of the modern astronomical satellites to tackle the limb darkening problem. My question therefore to de Jager was, are the solar astronomers still interested to know the limb darkening at the extreme limb, as people were in 1936?
DeVorkinYou have the letter -- his reply to you?
Wesselink:He said to me. "But of course you need a coronagraph. In space. Because you still have scattering in the instrument. You don't only have scattering in the atmosphere but you also have it in the telescope, which makes it very difficult to measure low intensities near the solar limb. So you need a space telescope which is a kind of coronagraph, and that doesn't exist yet," he said. I think that was one of his reasons to think that a space telescope was not yet adapted to this problem.
DeVorkinBut it could be in the future?
Wesselink:But it could be.
DeVorkinTo his knowledge, then, it is something that the solar astronomers would want to have still.
DeVorkinVery interesting. Now, during this time you were also working on your thesis, is that correct?
Wesselink:Yes. I published my thesis in 1938 in Dutch. Then I went to the United States, to Yerkes, also in 1938, and met Struve and Morgan and Henvey and Greenstein and Kuiper -- all the people who are important in astronomy nowadays were gathered there, in some function or other.
DeVorkinDid we talk about how you decided to go to Yerkes?
Wesselink:Well, I was invited by Kuiper in the first place. He did invite me to come over there.
DeVorkinWhen you were there, you realized that you were going to return to "Holland, to Leiden, is that true?
Wesselink:Yes, I wanted to return, rather, to Leiden, and I did. In 1939, February, I returned to Holland. After having published a paper on relaxation oscillations, as a cause of Cepheid variables. We did talk about that.
DeVorkinYes. And that leads us into talking about your method known as the Wesselink method for Cepheids. I cannot recall if we talked about that in the first session.
Wesselink:No, I don't think we ever did talk about that at all. That work was done during the war, during the German occupation at Leiden, when I could not observe. Nobody could observe because there was no electric current available in Holland, for many years.
DeVorkinThere was no current at all, or not enough?
Wesselink:There was no current at all? I mean, people were without light and power for at least three years of the five year war.
DeVorkinHow were hospitals maintained, by generators?
Wesselink:I think they must have had local generators.
DeVorkinBefore we get into that, let me ask you one question, you came back in 1939. You wanted to come back to Leiden.
DeVorkinDid you know at that time that there was going to be the German invasion or anything like it?
Wesselink:No. I didn't know it.
DeVorkinIf you did, would you have tried to stay at Yerkes?
Wesselink:I cannot remember. I'm not sure.
DeVorkinLet's go then to wartime conditions in Holland, and I'm very interested how you fared, your family, and astronomy during the war. Wesselink: Well, during the war astronomy in Holland was of course greatly reduced, because of difficulty with observing. Without power you cannot operate modern telescopes. Furthermore it was very difficult to obtain photographic plates. Note this was available from the United States. You couldn't get any Kodak material, for instance. But of course, there were plates available manufactured by German factories, and we sometimes really did purchase photographic material from Germany, but by the time they arrived in Leiden, these boxes with plates were quite often bombed and therefore not very useful any more for astronomy. So all in all, we couldn't observe very much. So I decided to do something, besides trying to get food for myself and the family.
DeVorkinWere you married at that time?
Wesselink:I married in '43.
DeVorkinOK, we'll get to that then.
Wesselink:I decided that I should do some work in more theoretical directions. Then 1 started work on what people call now the Wesselink Method. But that was not published until after the war, because all publications were stopped during the war. Nobody could publish anything because it was impossible.
DeVorkinYou were still going to the observatory daily?
Wesselink:No. There was no heat. In the winter there was no heat in the observatory, so you couldn't be there. It was impossible to work there, so astronomers just didn't go to the observatory any more,
DeVorkinDid they get together?
Wesselink:They did get together sometimes for a colloquium. That happened. Yes, we did get together on one occasion; I still remember a very important colloquium, with van de Hulst announcing the possibility of the 21 centimeter radio line, due to hydrogen, which was later of such great importance in radio astronomy. So we really worked all by ourselves, I suppose, at home or when occasion permitted you worked in astronomy. The other thing I started then, was being interested in the heat conductivity of the lunar surface. That eventually resulted in a paper in which I derived the coefficient of heat conductivity of the lunar surface material, and concluded that the surface of the moon must be covered with powder, because only powder in a vacuum has a heat conductivity of the same order of magnitude as I found from that analysis.
DeVorkinWhat were you basing your work on? Was it Petit (Pettit?) and Nicholson's work?
Wesselink:I used Petit and Nicholson's measures of temperature that they made during the eclipse of the moon.
DeVorkinThis work was done in the thirties, wasn't it?
Wesselink:Yes, Petit and Nicholson's work was done in the thirties -- that was many years before I started calculating.
DeVorkinSo you already had the material in journals at the observatory?
Wesselink:The material was available at the observatory during the war.
DeVorkinAnd you could go during the day, let's say to the library and use the library?
DeVorkinLet me ask you this kind of question. I can see how your development of the Wesselink Method grew out of your early Cepheid interests, interest in variable stars, but working on the lunar surface is a very different type of a thing for you to do, and I'm just interested in how you came to be interested in this.
Wesselink:Well, I can tell you that because one of the students gave a talk during the war on Petit and Nicholson's work. And in the discussion at the colloquium, Oort was present, and I made some critical remarks on this lecture, and Oort turned around and told me to do better. I said, "I will," and from that time on I started to do it.
DeVorkinIt's been proven correct, hasn't it, that your model really held true?
DeVorkinHow did you feel when you heard about that?
Wesselink:Well, I was of course witnessing Aldrin descending on the moon, in 1969. The first man on the moon. I saw it on TV. He came down from the steps out of the capsule, and put his foot down on the lunar surface, and left an imprint in the dust layer. And there was no question in my mind: that proved my point, that I had found out years before, that there was really dust on the moon.
DeVorkinSo you used their data, and from that determined the heat conductivity characteristics.
DeVorkinTo know that it was dust, though, you would have needed some laboratory information.
Wesselink:Well, I did have laboratory information, but it took me some while to understand that only dust would provide the very low value I had found for the moon. The value found for the moon was so exceptionally low, there was no substance ever measured on earth that could rival that. And so I made a bigger search and scratched my head: "what possibly could the moon be made of, to get such a low amount of conductivity. Then I finally found a paper by Smoluchowski.
DeVorkinIs that referenced in your paper?
Wesselink:That's referenced in my paper. He had measured the heat conductivity of powders in a vacuum, And in a vacuum, the heat conductivity is much lower than in normal air pressure. And suddenly, there was a spark in my head, realizing that the moon of course has no atmosnhere, and that must be the the clue to the problem. So everything came right, by believing that it was a powder in. a vacuum.
DeVorkinWhen you made this discovery, did you report on it in the colloquium? Was this still during the war?
Wesselink:No. I never reported about this study in the colloquium. Never did.
DeVorkinDid you discuss it with anyone, with Oort or anyone?
Wesselink:I showed it to him when I had finished writing the paper.
DeVorkinWhat was his reaction?
Wesselink:Well, he approved of it. I don't think he gave me much comment on it. But he said, "That’s all right, you can publish that."
DeVorkinIs that the way things went, that the director had to pass on anything that was published in the observatory?
Wesselink:I think so, yes.
DeVorkinWas that acceptable to everyone?
Wesselink:Yes, I think that was a good policy. It was acceptable to everybody.
DeVorkinDuring this period in World War II, I've heard that Oort was involved with the Resistance in Holland. Do you know anything about that?
Wesselink:Well, Oort resigned from the university.
DeVorkinWhen was this?
Wesselink:In 1940. Because of the Nuremberg laws. The Nuremberg laws were introduced in Holland, and at the university there were some Jewish professors who were dismissed by order from the Germans. And then when that happened, all the university professors resigned en bloc, Oort included. But Hertzsprung did not resign.
Wesselink:No. He did not resign.
DeVorkinDid he give his reasons?
Wesselink:Yes. His reason was that in the first place, he was not Dutch, he was Danish and had nothing to do with it, he said. Furthermore, he said, "It does not serve any useful purpose, in my opinion," he said, "by going." Well, people can debate about that decision. Maybe it was a good thing that he stayed on, because there was someone looking after the observatory when he stayed. But Oort left, and went into hiding during part of the war, just because nobody was ever certain what would happen especially if you were a professor from Leiden University who had resigned because of the Nuremberg laws. They were afraid that it would make him hostage and shoot him at any provocation. So he was out of the way. But he went on working hard, and I met him several times during the war. As a matter of fact, he asked me to review all the publications made in Holland during the war, which were not yet published, and then send the information to the United States if possible. And I did that, I sent letters to B. Lindblad in Sweden, with the remark that he should show it to as many astronomers as he could think of, without specification.
DeVorkinDid this take the form of a review or newsletter?
Wesselink:A newsletter. This was called THE NEWSLETTER.
DeVorkinYou sent it to Lindblad?
Wesselink:I sent it to Lindblad in Sweden, which was a neutral country. And Lindblad got the message and sent it on straightaway to the United States.
DeVorkinDo you know who he sent it to?
Wesselink:I think he sent it to Bart Bok.
DeVorkinOf course. Bok was running the NEWSLETTER at Harvard at that time.
DeVorkinLindblad was able to write to you?
Wesselink:Lindblad never wrote to me about it. He didn't want to give the linkage away or something, because of course, the Germans didn't quite understand. But they must have looked into it. They certainly must have seen my reviews, but being astronomical they wouldn't have understood it.
DeVorkinThese were printed or written reviews?
Wesselink:Typewritten. There was nothing mentioning the United States in my letter. Nothing at all.
DeVorkinBut you figured that in writing to Lindblad, he would get the message, which this should go to the United States.
DeVorkinDid you write to him in English?
Wesselink:I wrote to him in English, And he did get the message. There was never a problem. All the papers, all the important things that Oort found during the war about the distribution of the RR Lyraes and the distribution of the red giants in the direction in the galactic centre came through. They were already known in the United States before the end of the war.
DeVorkinDo you think the Germans ever wondered? They appeared in Bok's NEWLETTER, I imagine?
DeVorkinThen I assume the Germans would be able to get hold of that NEWSLETTER. It was freely distributed. Would they ever wonder how they (Bok) found out what Oort was doing even though Oort was in hiding?
Wesselink:Well, they might have. But I have never heard such a feedback or read about it.
DeVorkinYour letters were never stopped, to your knowledge.
DeVorkinAnd the NEWSLETTERS continued.
DeVorkinDo you have copies of those letters?
Wesselink:No, I haven't got any copies. I'm very sorry about it now. But I haven't.
DeVorkinWhat I may do is go to Harvard Observatory, and look for the NEWSLETTERS they have. They would have copies if anybody does. And then see what did come through from Holland.
Wesselink:Yes. I don't know how many I wrote. Not that many. Maybe four or five, I think, in all, because I started rather late in the war doing all that.
DeVorkinWhat was your position? Were you in hiding too? Did you resign from Leiden, or you didn't have a professorship?
Wesselink:I didn't have a professorship in Holland. I didn't resign. There was some question whether an assistant should resign or not. But the professors and Oort and Hertzsprung said, "Don't, because it would be much better that you stay on and look after the property." And we didn't resign. Every man in Holland was vulnerable all the time, during the war, because you could be taken from the street and sent to Germany for slave labor, any time.
DeVorkinDo you know if any astronomers were actually taken?
Wesselink:There wasn't a single astronomer ever taken up from the streets. Because they were always warned that well. The Germans were so systematic, in their "Razzia's" as we called them --
Wesselink:Yes. They were so systematic that one always knew hours in advance when they were busy taking people. My wife always found my hiding place, which was in the observatory. I don't think the Germans would ever have found me there.
DeVorkinYou had a specific hiding place?
Wesselink:I had a specific hiding place, yes, which was in the observatory.
DeVorkinWhere was it in the observatory?
Wesselink:It was above the ceiling of the first floor, and below the floor on the second floor.
DeVorkinNow did you get in there?
Wesselink:I got in there by going first to the second floor. There was a hole I could get in easily, and I could not stand in that space, but it was roomy enough that I had a bed there and I had water there and I had some food there always fresh. I kept it fresh so that I could stay there several days without showing myself.
DeVorkinWhen you were there in the observatory, were the Germans ever actually searching the observatory'?
Wesselink:No, they never had been searching the observatory. They had been searching the houses in the observatory area. But that was because the Underground was housed at the observatory for at least a year. The Underground movement from Leiden had nothing to do with observatory work at all.
DeVorkinCould you describe what that was?
Wesselink:Yes. They printed a newspaper. Young men, one of them was an astronomer printed it.
DeVorkinWho was that?
DeVorkinThat's more of a German name, isn't it?
DeVorkinWhat was his origin?
Wesselink:Well, I think he was Dutch, but he was still a student, and went into Underground work. As a printer of fact, he lived in the apartment which I had vacated at the time I married. And in those rooms, the newspaper was printed and circulated throughout Leiden all the time. And the Germans once went to these premises and knocked at the door, and asked, "Can we have some blankets for the East Front?" The Germans on the East Front were in bad need of blankets. But of course, there was a tremendous fright by the people opening the door to find a German at the door. They may tell have some other reasons -- that they had found out that that was an Underground site. But they never found out. They gave them blankets, and the German turned around and left, without ever finding out what was going on.
DeVorkinThat's fascinating. Why do you think the observatory was never searched? It never entered their heads? You say they're so systematic?
Wesselink:Well, I think they were never betrayed probably, because it was only through betrayal that the Germans had any information. Of course betrayal, you have to consider, was usually done after torture. People did betray; even very good people did betray, but only after torture. We have no imagination, what the Germans could do to you. It was terrible. So, we were aware that as soon as some person who knew the observatory site for the Underground also know of some person who had been taken by the Germans, everybody fled from there, for at least 14 days. We knew that there was a great danger that he would betray.
DeVorkinWas Oort involved with that newspaper at all?
Wesselink:Not at all. I don't know what Oort did during the war.
DeVorkinNow, during this period, did you meet your wife. Had you known her before?
Wesselink:Yes, I had known her before, and we had a house in Leiden, in the Groenhoven strasse, which was opposite the observatory, there was water in between. And she came to visit me then I was in hiding, because the water had frozen, the canal had frozen, and she walked across with foodstuff and brought it to my hiding place.
DeVorkinThis is before you were married?
Wesselink:No, this is when I was married.
DeVorkinHow did you meet your wife?
Wesselink:I met my wife when she was visiting a friend at the observatory. Our first meeting.
DeVorkinWas her background anything similar to science?
Wesselink:No, I do not think so. She was a friend of the daughter of my professor. But my wife's background is not scientific.
DeVorkinThe daughter of your professor would he Hertzsprung's daughter.
Wesselink:Yes, She knew Hertzsprung's daughter.
DeVorkinHow long was it before you decided to get married?
Wesselink:Well, I think about a month. Not very long.
DeVorkinCould you associate freely socially during the occupation?
Wesselink:With other people in Holland? Yes, you could. No difficulty there.
DeVorkinAnd you were married during the occupation?
Wesselink:Yes, I was just married during the occupation. We had a marriage reception in which there was very little to offer, though. I mean very little foodstuff to offer. But we still had a reception.
DeVorkinWho came to that reception? Were there many astronomers?
Wesselink:Astronomers came, and relatives. I think the observatory was well presented. All those who were at Leiden at the time. And my wife worked before she was married, and all those people from that institution were also present.
DeVorkinWhat was her position? What did she do?
Wesselink:She was a chemical assistant in a laboratory for the government, for checking on dairy produce. All samples from all over the country were collected there and examined for their quality. There was continuous testing of butter and milk and whatever was available. Of course that had some advantage in a time of shortages, because these samples could still be used on your bread. They were distributed after the sample had been tested. There was enough over so that the people working at the institute were given butter, milk and cheese.
DeVorkinHow scarce was food? Sounds as if it was pretty bad.
Wesselink:Well, food became scarce only during the last year in '44 as a reprisal by the Germans, because the Dutch started a railway strike. The Dutch railway system struck, of course with the intention of hitting at the German war effort. The Germans couldn't operate the Dutch railway system, because the signaling on the railways is altogether different in Holland than it is in Germany, and therefore there were a lot of accidents when they started doing this. But as a consequence, the Germans thought up some scheme where the population should not have any more to eat. And they told the populace that as soon as the railways would run again, they would get normal foodstuffs again, claiming that they couldn't deliver the food because of the strike; that the food had to be transported by the trains. And as a consequence, we didn't get anything so long as the Dutch trains didn't run. The fact is that food in Holland is never transported by trains but by boat. So this was just what you call eyewash, an excuse, to the population.
DeVorkinHow did you get food?
Wesselink:We got food by long walks and by bicyc1e, going into the country, going to the peasants themselves, and arguing and debating with them for a long time, sometimes giving them things, not money, because they had enough of it, but things they couldn't get otherwise, things you may have which they would like to have -- for instance, clothing that you still had and that was worth having, you could exchange that for food. I always managed to get just enough. I was very lucky. When I ran out of food, almost the same day I would have some more. Always just.
DeVorkinHow much of your time was given over to getting the food?
Wesselink:A tremendous amount of your time was taken by that. It was an incredible situation. Your wife didn't know of course what was happening to you. I was away for three days on one occasion, in the country. And you never return, because some German may pick you up for slave labor in Germany, and then your family wouldn't be told. So as you stay away for some while, the wife didn't know what happened, or anything.
DeVorkinThese journeys were by foot? You would walk?
Wesselink:Well, on that last occasion, I went by bicycle. I went to the Amsterdam area, and I got food which was sent on to me from Gronigen by boat over the Zuider Zee, with a very proper address on it. The address was for some orphanage. The orphanages were kept well fed, and the address was an orphanage, although it was meant to be for me. That was agreed upon. It was all done to cover up the assignment. So I got my stuff, and when I came in the neighborhood of Leiden with it, it was a very heavy load. It was almost taken by a German who held me up, just at the very edge of Lieden, and he stopped me and he said, "That's food. You'd better give that to me.'' Now, what could I do but stop? Then he asked me what was in that and I said, "Capuziner" because I thought that was the German word for the Dutch word: honen which is a kind of bean.
Wesselink:No, not coffee bean, but a kind of pea, you see. He got so fed up with me that he didn't want to be bothered further, so he sent me on. I'm very happy that he didn't bother about my food. I had my food. I looked up in the German dictionary, what "Capuziner" meant, and that was nothing to do with peas and nothing to do with food at all, But the German word "Capuzinerr" means a kind of dried flower. So obviously he was not interested in that. And that was my luck. Still I had not lied.
Wesselink:Sort of, help from above.
DeVorkinYes, exactly. Do you have any other impressions of your scientific experiences during the occupation? The effect of the war on science, on astronomy, in Holland.
Wesselink:I think the Dutch astronomers went on in their business quite well. I think it wasn't so very good in Europe generally. German astronomy was very badly hit, I think. And still is feeling the effects. Maybe.
DeVorkinIn what way?
Wesselink:Well, I think German astronomy was completely stopped during the war. All the German astronomers had to fight.
DeVorkinIn research and right on the line?
Wesselink:Yes. Yes. So we got offers from the German High Command of going to Germany for three times the salary we were receiving at Leiden.
DeVorkinThis was during the war?
Wesselink:Yes. To replace the German astronomers who were called up for military service.
DeVorkinDid anybody take that offer?
Wesselink:Nobody took the trouble even replying to that letter.
DeVorkinYou were still employed at the university then?
Wesselink:Yes. I was still employed at Leiden all the time.
Wesselink:Regardless whether you showed up at the observatory or not.
DeVorkinWhere did they get their funds to employ people?
Wesselink:That was a most interesting and intricate thing. But that has been described. There has been a book explaining how all kinds of people were being paid during the war in Holland although they didn't give any services. All these professors who had resigned, for instance, didn't receive salaries anymore, but still there were funds available all through the war for these people.
DeVorkinWhat's the name of the book?
Wesselink:I do not know. I cannot recall it.
DeVorkinIt's a book in Holland?
Wesselink:It is a book in Holland, and I know a person who would know. I could ask him. He once gave a lecture on this topic -- how all that Resistance work was funded.
DeVorkinWho is this man that gave the lecture?
Wesselink:The man who gave the lecture is Bruins. He's not an astronomer. He's a friend of mine.
Wesselink:In Holland. I think the funds came primarily from the banks, in the understanding that the government would refund them later if the government would return, and the government did.
DeVorkinWhat was reorganization like after the war, after the occupation was over? Did you have meetings to try to figure out how to begin work again at the observatory? Were there people opting to go in different directions in astronomy?
Wesselink:Well, soon after the war, of course Oort came back, and he became director of Leiden and started directing immediately. Everything was of course completely disorganized. Holland was completely disorganized, and in the first few months there was still a lot of starvation. We didn't just have food immediately, although the United States helped tremendously. We were sent food parcels all the time in the beginning. But still people died, because the distribution didn't yet exist. You just don't feed such a big population of 12 million overnight. And science and astronomy gradually started picking up.
DeVorkinDid the BAN cease publication during the war?
Wesselink:I think it practically ceased, yes, that's right. But then it picked up after the war again, for a great number of years, before it stopped publishing, with the advent of ASTRONOMY AND ASTROPHYSICS, of course, but that was much later.
DeVorkinOh yes, that was in the seventies or sixties. I'm interested in restructuring after the war. Was there any change in the nature of astronomy at Leiden, in your feelings, after the war? I know that you left.
Wesselink:Yes, there was.
DeVorkinWhat were the changes?
Wesselink:The change was primarily that radio astronomy was energetically introduced, I would say. We didn't have radio telescopes; Holland didn't have a radio telescope yet. But Oort was quick making the government not allow the radar equipment of the Germans to leave the country. So the German radar telescopes were kept in the country and were put to radio astronomy use, and the first radio astronomy was done with these things. The occupation ended in May, '49 with the collapse of Germany. Only then were we liberated. We were not really liberated by any army. The army did not invade Holland -- Germany capitulated, and then the Germans just left and the Canadians came in. We had a Canadian occupation for some while.
DeVorkinHow was that?
Wesselink:That was quite quite good, quite pleasant.
DeVorkinNow, within a year after that to fix the date, you moved to South Africa.
Wesselink:Yes. I mean, I was told that my new position would be "Observator" from Leiden at the Dutch station in South Africa.
DeVorkinDid this have anything to do with your plans in 1940 to go to South Africa?
DeVorkinThis was just a coincidence?
DeVorkinWas this Oort's decision, to send you down there?
DeVorkinAnd how did you feel about it?
Wesselink:Well, I don't think I was very keen. I had some moderate enthusiasm because I knew that this would leave very little time for my own scientific aspirations. I would have a lot of observing work, the plates would all be sent to Holland for inspection.
DeVorkinThe reductions would be done in Holland.
Wesselink:The measures and the reductions and the discoveries would all be done in Holland. But one of my major assignments was taking plates for a vast photometric program of all the selected areas in the Southern Hemisphere. I think there are about 140 selected areas, and I photographed them all, and connected them in a vast photometric scheme with standard areas, with gratings, and this was all measured at Leiden under the supervision of Osterhoff, and it was published in the ANNALS of the Leiden Observatory. Osterhoff has published that. Photometry in the selected areas was done photographically although some standards were done photoelectrically. That was my major work, taking all the plates for that program.
DeVorkinHow long did that take?
Wesselink:That took four years.
DeVorkinSo it was well into about 1950?
Wesselink:Well, no, I mean in '49 I knew already that I was going to Radcliffe Observatory.
DeVorkinHow did you get that?
Wesselink:I got my first photoelectric photometer in the Leiden Station, but I couldn't get that thing to work. That was sent on to me from Holland, but that had never worked, I suppose, and it didn't work, and I spent a lot of time on that thing, unfortunately. I think at the end of 1950, I went to Radcliffe on the invitation of the Radcliffe Observatory as their chief assistant.
DeVorkinDid you have any second thoughts about leaving the Leiden staff at that point?
Wesselink:No, not much, because my contract was that I should come back to Holland for some years, and then go back to South Africa. I was concerned with how to educate my children under these circumstances. And I couldn't visualize that under this scheme.
DeVorkinThese are your own children.
Wesselink:My own children. And I decided that I was much better off staying in South Africa at the Radcliffe Observatory, and doing my own research, rather than taking plates every night.
DeVorkinLet me ask you something about that period. It was about in that year, '50, ‘51, which the Boyden Station was closed down there in South Africa. And Bok had been down there for quite some time with some of his students, working. At the end of that period, the Boyden Station closed. Were you in contact at all with Bok, and did you discuss with him at all the fate of the observatory down there and why it was closing?
Wesselink:Well, I met several observers at the Boyden Station during the four years I was in Johannesburg. I met Ivan King. Ivan King was there as an observer at Boyden. You know Ivan King?
Wesselink:And I met Karl Henize. He was in Bloemfontein at the Lamont-Hussey Observatory with the 10-inch telescope, doing his important work on emission line objects in the Magellanic Clouds.
DeVorkinYes. The contact there might be interesting because they were working with the early photoelectric photometry equipment.
Wesselink:Ivan King was working with early photoelectric equipment which in the first place, had been designed I think by Linnell. And King considered it very highly. I think Ivan King was a good photoelectric observer, and got most of his photoelectric education through Linell's thesis. I talked a lot with Ivan King at that time.
DeVorkinDid your own interest in photoelectric work increase through your talks with King?
Wesselink:Oh yes, very much so. But I didn't have the equipment, myself. I didn't have the time. My function was taking plates for Leiden, and it was more efficient, that Leiden should construct photometers and everything and send it on to me, if I ever should do so. But I never used much photoelectric equipment at the Leiden station. Walraven came after me and he was the expert, of course, on photoelectric photometry.
DeVorkinLet me ask you about your knowledge of the state of the Boyden Station, then.
Wesselink:I went over to the Boyden Station in '48, together with Thackeray, and visited Paraskevopoulos, and saw the telescope which I think had been installed there. The ADH, that is the Armagh, Dunsink, Harvard telescope, which was sent down there I think primarily and the initiative of Bok. And Bok was there to install it, with Paraskevopoulos of course. I don't know how much use has been made of that telescope, but it was supposed to be a very good telescope,
DeVorkinThe fact is the whole thing closed by '51.
Wesselink:I don't know the exact year in which it closed. I think it was closed because of lack of interest from Harvard University in the station. Harvard University considered that the Boyden Station was too expensive to be kept up by Harvard University. And then of course you know what happened. The Boyden Station was taken over by a group of observatories in Europe with Harvard. But at this moment, I think it is closing down completely. Isn't it?
DeVorkinThat's what I thought, yes. Well, you moved to the Radcliffe Observatory. Did you see greater opportunity to do your own work there?
Wesselink:Oh yes. I was much happier, because Thackeray and I got on very well and had common interests in discovering RR Lyrae variable stars in the Magellanic Clouds. The very important issue, whether there were or were not RR Lyraes in the Magellanic Cloud had not yet been solved at that time. Shapley said, "There aren't any." He made this statement some years before, that there were no RR Lyrae stars in the Magellanic Clouds. Because if they were there, he would have discovered them, because he expected the RR Lyraes at magnitude 17-1/2. That is the distance modulus given by Shapley for the Magellanic Clouds.
DeVorkinI see, and RR Lyraes being at zero absolute, then they would be at 17-1/2.
Wesselink:That of course is on the basis of zero absolute magnitude.
DeVorkinThat's what they thought.
Wesselink:That's what I thought too. And because his photographs went to 18, he didn't see any RR Lyraes, so here we have a system with no RR Lyraes. So our enthusiasm was great in discovering them at a fainter level. We said, "This may be at a fainter level, that the distance modulus was wrong," That was our opinion. There might be a possibility that there are there. And when I arrived in December, 1950, at the Radcliffe, Thackeray had found RR Lyrae variables, I think three or four, in NGC 121, which is a faint globular cluster near the Small Cloud, and presumably was at the same distance as the Small Cloud, he was thinking that this may very well be, because there were several globular clusters, very faint globular clusters near the Small Magellanic Cloud, and the large one which were presumably at the distance of the clouds but there was not much known about the globular clusters. Of course the stars were very very faint.
DeVorkinBut would it be better to look at a globular that wasn't right in the vicinity of the cloud, because the background would be less.
Wesselink:The background would be less interfering. Well, at any rate, I started discovering RR Lyraes in 1978 and NGC 1466. And in NGC 1466, I discovered about 40 RR Lyraes, which is a tremendous lot, and we discovered some more in NGC 2257.
DeVorkinYou also in the later fifties started finding RR Lyraes in 47 TUC and others, but those are globular clusters in our own galaxy?
Wesselink:These were known in 47 TUC, but we wrote a paper later with M.W. Feast and Thackeray on their membership, which was a different thing. They were known. They were found by Harvard, but Harvard claimed that they were not members, and we started contesting that, saying they are.
DeVorkinSo in the beginning of your time at Radcliffe in the fifties, you worked on variables in the Magellanic Clouds and the dust content of the Magellanic Clouds.
Wesselink:Yes. Well let me say a few more words about these variables. When we had these RR Lyraes in the Magellanic Clouds, the next problem was finding out how faint they were. And I started measuring them without proper photoelectric equipment; I measured them and found that they were 19.0. That is a full 1.5 magnitude fainter than what Shapley claimed that they would been -- and that in the same 1.5 magnitude Walter Baade needed in his extension of the distance scale of the Andromeda Nebula. So we had amplified Baade's conclusion that the distance scale in the universe had to be multiplied by two, with a similar discovery, but this was the RR Lyrae stars in the Magellanic Clouds. That is the same thing as Baade found, about the same time in '52. There was a conference in Rome, where Baade first announced the extension of the distance scale, and Thackeray went to that conference, stood announcing our find of the RR Lyraes in the Magellanic Clouds.
DeVorkinDid Thackeray talk about the reactions of the audience when he did that?
Wesselink:Yes. He said, "Of course people were very interested," They thought that this was very good. So the next thing I did at Radcliffe was to determine in a new way the distance of Alpha Centauri. I wanted to very briefly tell you more about that.
DeVorkinThis was my parallax?
Wesselink:I measured the difference in radial velocity of the two components, A and B of Alpha, when at the time the spectrograph first arrived, the difference in radial velocity was at the maximum.
DeVorkinThat was the nodal passage?
Wesselink:The nodal passage, and it was a very opportune time to do this very thing. I mean, we have to wait for 80 years, in the moment it's still 60 years away, before we can do a thing again like that. And if I were alive in the 60 year time, which I have doubts, I would do it again, much better of course with the Coudé spectrograph which is available now. Anyway, I used the two prism Cassegrain spectrograph for the purpose, and got a very accurate value for the difference. But anyway, I got out a parallax, which is not better I would say than the trig. value, but it's of the same order of accuracy as the trigonometric value.
DeVorkinWere you able to choose these projects yourself?
Wesselink:Well. I proposed it to Thackeray, and he was very enthusiastic about it, and he said that I should go ahead with it, and I did that myself.
DeVorkinYou were in contact with van den Boss during this time.
Wesselink:Yes, because I needed a good double star orbit. What you require is the best double star orbit available for the purpose, because that comes in, and he gave me all the information. I also had contact with Hertzsprung, because he was still alive, he gave me his latest photographic measures. His were of course extremely important, better than the visual observations. That fixed the major axis which is important, an accuracy for the --
DeVorkinAccurate to 1 percent?
Wesselink:1 percent and you require therefore all the other elements of the orbit also to the same accuracy. Well, anyway, the other things at Radcliffe, I always enjoyed tremendously. Feast, Thackeray and I were doing radial velocities of B stars, all around the Milky Way, for the purpose of determining the constants of galactic rotation -- Oort's constants -- by using combining certain Southern Hemisphere data with Northern Hemisphere data, strengthening the solution of Plaskett. It had been done in the past by (J.S.) Plaskett in Victoria. Then I started my work on photometry of clusters. I took several other plates, and we had an iris photometer by then, and I did photoelectric photometry properly, with the help of the Royal Observatory, Capetown. They helped me photoelectrically to set up a good amplifier.
DeVorkinWho helped you?
Wesselink:Cousins helped me in getting me the equipment. The Leiden Observatory was kind enough to help me with the photometer. They built it in their shop. So I put that on the 74-inch telescope. Well, then of course with Thackeray and Feast and I, we did our well known work on the brightest star, in the Magellanic Clouds -- the supersuper giants. That had some importance for the absolute magnitude of such stars. Knowing the distance of the clouds, we got better absolute magnitudes for the brightest absolute magnitude stars can possibly have.
DeVorkinThe problem I have in using the SCIENCE CITATION INDEX to derive some of your bibliographical references is, I only have those where you are the first author. The work that you did with Feast and Thackeray on the supergiants, I don't have a reference to. Can you give me the approximate year that was done?
Wesselink:I think that was published in 1961. I have a copy of it here. So that was a cooperation between Feast, Thackeray and myself, Feast and Thackeray doing the spectroscopy and I doing the photoelectric photometry in the clouds. Then we wrote a paper together, the three of us, discussing the kinematics of the radial velocities -- the rotation of the Large Magellanic Cloud from radial velocities.
DeVorkinDuring this entire period, how was interest increasing in South Africa for astronomy? People were becoming more and more aware of the need to complete observational programs and continue work in the Southern Hemisphere. Was there a large growth of let's say native interest, let's say by the South Africans, Afrikaaners, in astronomy?
Wesselink:I think so, yes. I think there was a good flourishing amateur society in Pretoria, in Johannesburg, in Capetown, and in Durban. All the big cities had their departments of the South African Astronomical Society.
DeVorkinDid you participate, or do any popular lecturing?
Wesselink:Yes, I did participate in that, and I think all astronomers became president of that society for one year, one after the other. I was president I think in '63, and gave my annual lecture on Cepheid variables.
DeVorkinI know that when ESO was beginning, they were looking for a number of different observatory sites and that certainly South Africa was considered along with other sites. Where you involved at all in discussing this?
Wesselink:No. I was not. I'm sorry that I was not. Because once the ESO made a decision, and they made a decision to go to South America. I think they were afraid of the political situation in South Africa. I think that's the primary reason. I once discussed this with Blaauw. Blaauw's opinion was that the political situation in South Africa was not safe enough to have ESO there.
DeVorkinHow did you feel about that?
Wesselink:Well, at the time I didn't think he was right.
DeVorkinWhen was this?
Wesselink:A long time before I think even Blaauw was involved with ESO. In 1953 or something, he came over and I spoke with him, because in my opinion, the European view of the South African situation was completely out of proportion.
DeVorkinWhat were the conditions like, living down there? You were living in the community as well as working.
Wesselink:Yes, you were living in the community, and you were of course in close range with the apartheid problems. I mean, take the observatory itself, how was that organized? With black and with white workers. The astronomers, Thackeray had his own house at the observatory and I had mine. All belonged to the Radcliffe trust. Feast had his own house, and the mechanic had his own house. But we had black staff. They had their little houses on the observatory grounds, the black workers. They were gardeners mostly. The gardens were kept up by the black workers, and I think we were very friendly with one another, all of us. I got on beautifully with all the black people. As a matter of fact, I was put in charge of them by Thackeray, to deal with their passports and with their salaries. I was their chief for transport. We had an observatory car with a black driver, and I was supervising him. I told him where to go and who to pick up and who to bring down. He always saw me at a certain hour in the morning and in the evening, and I gave him complete instructions.
DeVorkinWas this rare for the blacks to have a residence in the area? Didn't most blacks have to commute from a black area into a white area to work during the day? Or this wasn't the case?
Wesselink:Yes. That's right.
DeVorkinSo was there any problem with the white community, in providing housing for the blacks?
Wesselink:I never understood that situation, why we had it and why someone else could not have that. I don't think we ever had any problems. I mean, I was involved quite a bit with their housing. As a matter of fact, I inspected the housing. I was much more involved even with their lives than anybody else, because if they were sick, you see, I went there and saw that, as a kind of a witch doctor, I considered myself. But when someone was really sick, -- if I really thought it was important I called in a white doctor to see them.
DeVorkinSo to your knowledge, there was no problem with the rest of the white community in your housing the blacks on the observatory grounds?
Wesselink:No. Only the wives I think were not there.
DeVorkinThe wives of the men who worked?
Wesselink:Yes. They were not there.
DeVorkinSo they were separated.
Wesselink:They were separated. Then I think that is one of the main objections, of course, against the apartheid scheme, see.
DeVorkinYes, sure. How did you feel about it?
Wesselink:Well, we all felt sorry for the situation, but we were thinking whether one could devise another scheme. There was a difficulty, you see. I mean, these people, when you have whole black families on your grounds, they have more complicated way of living, and very soon you get riots and quarrels among them. The quarrels among them are not negligible -- as soon as there are women around, also. We had native servants for the different people. The Thackerays had two native servants, what we call natives -- a black man and woman, working for them. We had one occasionally, because Nettie did not like to have a black servant. She would rather have none than have a servant with all the problems of that. "I want to do my own household," she would say. So our children were not brought up by black servants, something she didn't want to have happen. "I want to bring up my children." Most white people in South Africa who can afford it have black nannies and servants who do a lot of educating, put the children in the bath, give them food, and all kinds of things that we didn't want our children to have.
DeVorkinWhat about the Thackerays?
Wesselink:The Thackerays had the black servants. They had quite a say and quite a part in the education of the children. But I don't think it has done them any harm.
DeVorkinAre the children down there now?
Wesselink:No, there's one here.
DeVorkinHere at Yale?
Wesselink:Here at Yale. And he's going to stay in my house when I am leaving here on the 29th of this month. For 14 days, he's going to stay here. We know him. He's married, and we know that young couple very well, working at Yale. [Pause for lunch]
DeVorkinWe're resuming now after a nice break for lunch. We've been talking about conditions for research in South Africa and ESO, the European Southern Observatory.
DeVorkinAfter ESO decided not to come to South Africa, how did astronomy continue to develop down there?
Wesselink:Well, I think Boyden Station went on, and of course, you know the development of the South African Astronomical Observatory. Radcliffe was practically taken over by the British Research Council, and together with the CSIR, that is the Council for Scientific and Industrial Research, which was in Pretoria, it's a South African institution. They wanted to close Radcliffe and they did close Radcliffe, and Thackeray was of course discharged because of that and became a Professor in Capetown, and Feast went to Capetown. R.V.D.R. Woolley was the first director of South African Astronomical Observatory in Sutherland, but Woolley is retired now, and Feast took over as his successor.
DeVorkinThis is after Woolley left -- Australia?
Wesselink:Yes, sure, when Woolley left Australia, he went to England, I think, and from there, he went to South Africa. When Woolley left Australia he became Astronomer Royal, and he was Astronomer Royal for a great number of years. Then after he retired from being Astronomer Royal, he left for South Africa.
DeVorkinWhy was Woolley made the director and not Thackeray, do you feel?
Wesselink:I think Thackeray was probably opposed to the whole thing. Thackeray was satisfied with the site in Pretoria, and in my judgment, Thackeray was right only as far at spectroscopy was concerned, not photometry. The site was deteriorating continuously.
DeVorkinBecause of the growth of the town?
Wesselink:Because of the growth of the town in all directions. I had so many problems in 1964, getting anything done photometrically, because of the amount of light. The work on the faint stars in the Magellanic Clouds, to establish how faint the RR Lyraes were, was done only with great difficulty. And so I was in favor of another site for the observatory. And I left in '64, in the first place because I was being asked to come here, and furthermore, I thought that Radcliffe was not a good site for astronomy anymore.
DeVorkinWho asked you to come to Yale?
DeVorkinHad you known him over a long period of time?
Wesselink:Not for a long time. I met him in 1950, and Brouwer and Oort and van den Bos wanted a big observatory, with American-Dutch and South African money, somewhere on the Veldt in South Africa.
DeVorkinWhat happened to that?
Wesselink:That project failed because of Finsen. Have you ever heard of him?
Wesselink:Finsen said, "I don't like the project because that means that in practice, South Africa will have to pay the most. And the South African astronomers will have to do most of the work, to the benefit of the other countries." That was his opinion. The time service, for instance, for South Africa would be situated at the observatory, and would be run by South Africans, and the other astronomers would benefit from the time service, as done by South Africans, and he was just against it.
DeVorkinThe fact is, let's see, Yale had already placed a 26-inch telescope down in South Africa. Schlesinger's project.
DeVorkinWas Brouwer following up this interest that Schlesinger had?
Wesselink:Yes. But that telescope had nothing to do with the Union Observatory at all. That was independent of it on the university grounds. I know that place, but that was right in the center of Johannesburg and that was a very poor site too.
DeVorkinIt was in the center of Johannesburg?
Wesselink:Well, it was fairly close to it, yes. Dirk Brouwer wanted to have that telescope for his parallaxes, moved away from there, and Oort wanted my telescope, which I had in Johannesburg, the Leiden telescope, away from that site. So we all wanted to leave the city of Johannesburg, for the same reason. But Finsen, who was a South African, was against it, because he felt that South African would be subordinated to the foreign powers, as he called it. And his opinion was that certainly the United States has money enough, as he put it, to pay for it them. "If they want to build an observatory" he said, "let them do it. There's room enough in South Africa.''
DeVorkinAnd so the whole thing was canned.
Wesselink:Yes. Brouwer was very annoyed about that, and he therefore moved the telescope to Australia.
DeVorkinThat's when he moved it to Australia in 1950 approximately.
DeVorkinAnd so it was because of Finsen's negative feelings that the 26-inch went to Australia.
DeVorkinI noticed you had used some of Brouwer's work, especially on the position of the sun and moon, as early as in 1936.
DeVorkinHad you had any contact with him that early?
Wesselink:Yes, in correspondence about it.
DeVorkinBut you'd not met him until 1950?
Wesselink:I hadn't met him until 1950. That's right.
DeVorkinWhat was his interest in you in the fifties, in bringing you to Yale?
Wesselink:I don't know. He never said. I just suddenly got a letter, "Will you come here?" There it is.
DeVorkinWhat was your feeling when you got that letter? Did you try to see a way of staying in South Africa, or there was no question?
Wesselink:Well, I did discuss it with Thackeray. And my health was not good. I was unable to keep up the whole observing night with the big telescope. I just couldn't do it. And I foresaw that it would worsen in the years to come, if I kept that position, because there was no excuse. I mean, you had to observe. And that was also a reason why I wanted to leave, and I said to him, "I think I will accept this offer.'' Furthermore, I wanted to get my family away because in my opinion, South Africa will lose against -- whatever you believe -- world power. And I think finally South Africa will be given to the black people. I foresee problems of the same nature as in Rhodesia and I don't want to have my family involved.
DeVorkinYou could see that as early as 1964 easily.
Wesselink:That's my opinion. Yes. And that's why I told Thackeray, that I want to get them out. "If I do it now, it's possible," I said, "If they start marrying here in this country, it won't he possible.''
DeVorkinSo did your entire family come to the United States, or did your oldest son go elsewhere?
Wesselink:Well, my oldest daughter was already in Holland, because I sent her to Holland in ‘62, which was for two years, just for widening her education, in my opinion. And then she married a Dutchman, so she's safe. But I was still there with my son and youngest daughter, and we came over to this country in '64, see.
DeVorkinNow, when you arrived here, had you known that Brouwer was building the 40-inch telescope at Bethany?
Wesselink:He had written about it to me.
DeVorkinWhat were your ideas in using that telescope here?
Wesselink:I wanted to use it for a kind of photometry. I first wanted to have a simple photometer which would not be very suitable even for this climate, but there was nothing in the beginning, and I felt that we should just start doing something.
DeVorkinBrouwer had built that telescope with a design for parallaxes, really, for proper motion work, is that correct?
DeVorkinMainly interested in astrometric applications.
Wesselink:Yes. But I think I did some changing there. I told him that we should do something more modern.
DeVorkinWas he receptive to that?
Wesselink:Yes. He was. He was receptive to that. But I also knew about the telescope in South America, at El Leoncito, the astrograph for the big proper motion program, and I wanted to get my fingers on that too, but he said "No.''
DeVorkinHe said no?
Wesselink:He said, "that is earmarked for the proper motions." And I got the impression that he didn't want me to have anything to do with that. Of course, when he died, I became the scientific director of that project.
Wesselink:Because Gerald Clenence didn't want to be involved with that project, and someone however had to be involved at Yale with it, and that was supposed to me, and I was involved all the rest of the time. I'm sorry about that. That's all right. It's a good program. But I think they could have done more investigations of direct interest with it, because it's an excellent telescope for photometry also.
DeVorkinAfter Brouwer's death, how did the department change?
Wesselink:Well, after Brouwer's death, it was R. Wildt who became director. You remember him?
Wesselink:And then, the difficulty was that I don't think, there was much direction in those days, because everybody was waiting for a new director to be nominated.
DeVorkinYou mean, they realized that Wildt was an interim director?
Wesselink:Yes. Wildt considered himself an interim director. And he said, "I'm just keeping things going." Everybody kept his fingers crossed concerning who would be the new director, and of course the new director would give new directions, and one didn't want to start big programs which had to be stopped after the coming of a new director.
DeVorkinMeanwhile, what was the support for Bethany? You were directly involved in running Bethany at that time?
Wesselink:I didn't have any support. It was extremely difficult in those days. Even NSF was concerned about the absence of a firm direction, that Yale couldn't make up its mind who was going to succeed Brouwer, and Yale was not at all sure what they wanted. You see, Yale University was undecided and had no plans. They wanted to do away with celestial mechanics, which was a major, a major thing.
DeVorkinThe University wanted to get rid of celestial mechanics?
DeVorkinThis was during the period when it was needed for the space program, more than anything, Wesselink: Well, you know, after Brouwer died, Yale University was looking for a successor to Brouwer, and that successor was certainly not going to be a celestial mechanic.
Wesselink:Why? Because Yale wanted to be in the current astrophysical stream, of evolution and more theoretical astrophysics, and not in celestial mechanics. They wanted nothing to do with it. And I think that uncertainty in those days was felt everywhere. All the people in Washington thought: "Let's wait until these people have a new director. a firm new director."
DeVorkinI see. Wesselink: I mean, it was devastating. I looked at this situation. I hope it doesn't last long. I looked in my own files, that I still had unpublished, from Radcliffe, in which there were still some things, and I started working on that and writing it up, and gave classes. I spent my time that way, you can say, waiting also for things to develop.
DeVorkinWhat direction did you see? Did you have any particular choices in mind for director? Who would succeed Brouwer?
Wesselink:No. I didn't have. I had not foreseen such a drastic reduction of celestial mechanics as has happened. I thought some reduction of celestial mechanics was good, because too big a part of Yale was involved with celestial mechanics.
DeVorkinWell, Wildt always maintained his astrophysical work.
Wesselink:He maintained theoretical work.
DeVorkinHarlan Smith was here too?
Wesselink:Harlan Smith did radio astronomy. And I suppose that was very very good, all of it.
DeVorkinWas Smith still doing radio astronomy when you came? Wesselink: Smith wasn't here then, he had just left when I came.
DeVorkinOh, I see.
Wesselink:So my first student was Milone, and he was working on his PhD, and he was working with the spectrophotometer of Rodman?
DeVorkinYes, James Rodman. Well, then when Demarque finally came in 1968, how did the situation change?
Wesselink:Well, I don't know, whether I would like to go into that. It might get somewhat too personal, and I would like to avoid that.
Wesselink:I was not happy. I was not being backed up as far as Bethany was concerned. I did do things in Bethany but I was never backed up with things. Orders were given, behind my back, frustrating what I was doing, because it was considered a people's observatory where everybody could go and do what he liked. And I had some plans which I wanted, to develop the place, and I couldn't do it. Not enough power. And of course, McClure was then appointed, and he's very good and young.. And then of course there was less incentive for me to develop Bethany less and less.
DeVorkinWhat about when they started discussing the removal of the 40-inch to the Southern Hemisphere?
Wesselink:Right. I was asked about that.
DeVorkinYou were asked about that.
Wesselink:Yes. And I was in favor of it.
DeVorkinYou were in favor of it.
Wesselink:Yes, because I saw at once their point, and I said that it is sad that we are losing the thing here, but it is the best thing.
DeVorkinWhat do you feel could be done with Bethany?
Wesselink:I think Bethany can be developed, in the way I have in that little draft that I showed you.
DeVorkinThis is the "Summary Remarks for a NASA Symposium"?
Wesselink:Yes. In Washington, D.C., June 1 and 2.
DeVorkinIf we can get a copy of that, it would be good to go into your file to back up and help diccuss what we have here.
DeVorkinOK. Well, we've come up pretty much to the present. Are there other things that you would like to add, about any of the periods we've talked about, anything that we've left out that you feel should be included?
Wesselink:No. I don't think so. I think we have covered very well.
DeVorkinOK. Thank you very much for the time, and as with the first session, you'll receive transcript to chop up any way you want, and I hope that you will have a good time with it. Thank you.
 By D. Gill and J.C. Kapteyn (Annals of the Cape Observatories III, IV, V, VI) (1896 ff.)
 "Photographic Observations of the integrated brightness of the Solar Crescent near Totality..." by J.G. Ferwerda, J. Uitterdijk and A.J. Wesselink. Discussed by A.J. Wesselink [B.of the Astz. Insts. of the Neth. 9 (1940) p. 81]
 "Stellar Variability and Relaxation Oscillations" APJ 89 (1939) p. 659.
 BAN 10 11946-43) #390 p. 351
 [Possibly Shapley too, but it is difficult to ascertain the origin of the idea. Shapley published commentary on construction and organization of the observatory.]
 Paper with M.W. Feast and Thackeray
 Baade, W. Trans. IAU 8 (1952) p. 397
 European Southern Observatory