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Oral History Transcript — Dr. John Strong

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Interview with Dr. John Strong
By David DeVorkin
At Amherst, MA
April 20, 1984

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John Strong; April 20, 1984

ABSTRACT: After reviewing his upbringing and undergraduate and post-graduate education, Strong (b. January 15, 1905) describes his work on the aluminizing process and other projects as a National Research Fellow and then Astrophysics Fellow at CALTECH and his relations there with George Hale, John Anderson, Milton Humason, and others. Strong next discusses his efforts at Harvard during the War on infrared detection, obtaining a professorship at Johns Hopkins after the war and continuing his research in the infrared area for the Office of Naval Research, role in the creation of the Laboratory of Astrophysics and Physical Meteorology, and assuming its directorship. He then reviews his efforts in balloon astronomy and other areas of study, relations with the Space Science Board, and opinions on the evolution of space exploration.

Transcript

DeVorkin:

To start with Dr. Strong, I know that you were born in Riverdale. Kansas, on January 15, 1905. I would like to know just to start out a little bit more about your family, who your father and your mother were, if you had any brothers and sisters, and what your home life and training was like. What were your early interests? Let's start with your father and mother.

Strong:

My father was one of the sons of John Strong — born in Pleasant View, Illinois. My mother was one of three daughters of Efrain Bennett — born in Indiana. The name of the town just slips me. I don't remember the details of how my parents got acquainted. After they were married they set up household in Pleasant View. My grandfather was a millwright and had both a grain and lumber mill there. My grandmother was a Horton and she descended from an engineer who had been prominent in the building of the Erie Canal. My own three sisters were born there. The youngest is now 90 — the only survivor of the three. They were 12, 14 and 16 years older than I. My father emigrated to Kansas in 1893 — by horse-drawn carriage. He settled in the Kansas town then called Mallory, later changed to Riverdale when it moved one mile east to coincide with the intersection of the New Rock Island Railroad, where it crossed the Missouri Pacific railroad. My father was sometimes an agent of the Missouri Pacific, a grain dealer and livestock merchant, and he fattened out cattle about every year. I was born in Riverdale. The doctor who delivered me came by sleigh from Wellington as it was snowing at the time. I was a large baby. [If you're interested, at that time Mrs. Swan came to see me and she said, "He'll never live, his head's too big." That turned out to be quite a good prophecy.] I had to leave home to go to high school at the county seat in Wellington, and after that I went to college for one year — in Wichita.

DeVorkin:

What was the name of the college?

Strong:

Friends University (Quakers). Of course I immediately became a Quaker.

DeVorkin:

What were you before?

Strong:

Methodist. I am now a Catholic, having been an Episcopalian and a Presbyterian between. The bishop who baptized me said I certainly touched all the bases.

DeVorkin:

What were your interests? Were you the first in your family to go to college? And why?

Strong:

My sisters went to college, but none of them graduated — I was the first. I went to college because I got interested in radio. My father wanted me to be a doctor or a lawyer, so he was behind me. I went to Friends University, and then I ran out of money. I did a course in chemistry and psychology from the University of Kansas by correspondence the following year.

DeVorkin:

How did you support yourself at that time?

Strong:

I was at home. And, I got a job locally as a timekeeper for a construction company. When I was in college I supported myself by washing dishes, and by delivering a morning newspaper: the WITCHITA EAGLE.

DeVorkin:

So you went to the University of Kansas eventually?

Strong:

I was out the year of 1921. Then I went to the University of Kansas. That was after a year of timekeeping, after I graduated, and graduate work. I transferred to the University of Michigan (in 1927). Kansas made a bigger impact on me than Michigan. I did more creative work at Michigan than I did at Cal Tech. When I had graduated from the University of Kansas (1926) and decided to go on to graduate school all of my father's friends said, "Fred Strong's boy is going to be an educated fool."

DeVorkin:

Why was that?

Strong:

Well, I was the only boy in the whole community who ever went to high school. I guess the Strongs and the Benetts were a kind of proud and arrogant bunch. Oh, there is an interesting story about my going into physical science.

DeVorkin:

Yes, I'd like to know that.

Strong:

My father wanted me to be either a doctor or a lawyer, and by all means, neither a minister nor a musician, which he had a low opinion of — being a cattle man, and grain dealer. When I went to the University of Kansas, one of my friends took me to the dissecting room of the medical school one day. The result was that day I didn't eat any lunch; and, I gave up my career in medicine! Then I told my father I intended to go into chemistry. He objected because his idea of a chemist was a flour-mill chemist — a chap who baked a loaf of bread every day. Professor Hamilton Perkins Cady, of the chemistry department at the University of Kansas, converted my father to chemistry. Cady was a great man who made a practice of giving liquid-air lectures — wonderful demonstration lectures — all over the state." He was stranded in Riverdale once, when he changed trains from the Rock Island to the Missouri Pacific (to go somewhere and give his lecture) and my father, who was sociable, got acquainted with him. He said, "My boy wants to be a chemist but I don't take a very good view of it. Is there any future in chemistry?" Cady did such a beautiful job on him that I never had any more trouble on that point.

DeVorkin:

That is great. so you started out interested in chemistry. Did you change to physics at Kansas?

Strong:

No. I had a year of graduate work at Kansas in chemistry.

DeVorkin:

So your bachelor's degree in 1926, University of Kansas, is in chemistry?

Strong:

In chemistry.

DeVorkin:

Was it physical chemistry primarily?

Strong:

Physical chemistry. I never had a course in organic chemistry, and when I became a senior my advisor, Professor Dains, said: "You haven't had organic chemistry yet. We can't graduate you in chemistry." I said, "Dr. Dains, I'm earning my way through school, and I don't want organic chemistry. If you don't want to give me a degree, it's all right with me. I came here for an education." And they not only gave me a degree but I was an instructor my senior year in chemistry, and they made me a Phi Beta Kappa prematurely. They allowed me to graduate in chemistry without organic chemistry.

DeVorkin:

Now, this is of course eight years after World War I, which was largely known as a chemist's war, where a lot of chemistry was shown to be extremely important. Did this mean that there were job offers for you, alternatives to going to graduate school, or what?

Strong:

One of my peers at Kansas — a physics major, Lloyd Young — had gone on to Michigan. He influenced me to go to Michigan after the summer of 1926. Prof Cady had arranged a summer job at Bell Labs in New York City. I was an effete Easterner that summer. The next summer I got a job at GE in Building 5, in Schenectady, NY.

DeVorkin:

Tell me first about the summer at Bell Labs. What did you do?

Strong:

I worked on the elastic properties of rubber, balata, and gutta perch. I later, at Kansas University, studied the elastic properties of sulfur and wrote a paper on my results — my second publication. I think it was. Well, I worked for Dr. Kohman. He was also a Kansan. He was the son of German immigrants to Kansas. His older brother had majored in chemistry and developed a method of making yeast for sour dough bread which became quite a financial success. Kohman's father, a farmer, influenced all of the Kohman brothers and sisters to be chemists.

DeVorkin:

The next summer, which I take was after a year of chemistry at Michigan —

Strong:

No. I was still at Kansas. I went back to Kansas for 1926-1927. Then I went to GE for the summer of 1927.

DeVorkin:

Was that Schenectady?

Strong:

Schenectady.

DeVorkin:

What was your work there?

Strong:

I worked in metallurgy that summer on hydrogen embrittlement of steel in turbine blades. Building 5 was a very inspiring place, with Longmuir and Collidge there with whom I had some contact. The Director of the Research Lab (his name slips me) came upon me once when I was sawing a spiral cut in a graphite tube to be the heating coil of an Arsem furnace. I looked like a chimney sweep. He simply asked, "You're the student from Kansas. aren't you?" I said, "Yes." and he said, "Are you having fun?" I said, "Yes." and he said, "Then everything's all right."

DeVorkin:

Steinmetz was there for a while.

Strong:

He was dead by 1927, I think. I never met Steinmetz. He was the grand old man of GE.

DeVorkin:

That's right. Now, you went back to Kansas and you got your degree.

Strong:

No. I had my bachelor's degree when I went to Bell Labs. After a year in chemistry at Kansas I went to GE. And then I transferred to Michigan.

DeVorkin:

Okay. And you went to Michigan primarily in chemistry in the beginning.

Strong:

No, physics.

DeVorkin:

Oh? So how did you make the switch to physics?

Strong:

I was influenced by Lloyd Young, my friend who had gone to Michigan a year earlier. As you well know Michigan was the place to go in 1928, '29, '30, because they had many great names there in the summer. Their avant guard professors were Uhlenbeck. Goudschmidt, and La Port from Europe; and Dennison and Colby locally. Lloyd Young told me that Michigan was the place to go. Prof. C.V. Kent at Kansas had himself gotten his PhD from Michigan.

DeVorkin:

And you went to the Michigan Summer School?

Strong:

Yes, after 1928. I worked in the Kansas wheat harvest the summer of '28; but I was in summer school '29 and '30.

DeVorkin:

And you found them very exciting and stimulating?

Strong:

Oh my yes. At Michigan I got to know Ehrenfest from Holland (and Ornstein); Sommerfeldt from Germany; Dirac from England; and Johnny von Neuman. Prof. Ehrenfest was in California as a visitor the first year I was there.

DeVorkin:

After your PhD from Michigan?

Strong:

After my PhD.

DeVorkin:

Did you by any chance meet such people as E.A. Milne, who also was at the Michigan Summer School?

Strong:

I remember Milne. He is H and K line Milne.

DeVorkin:

My interest is also to identify the origins of your interest in astronomy. I was wondering if perhaps some of the theoretical astronomers who were at Michigan —?

Strong:

No. I had absolutely no interest in astronomy then. Indeed, I never had a course in astronomy in my life — that is as student. I visited the Michigan observatory only once or twice. Dr. Alter at Kansas, and two students were my first influence. One of the students later became the discoverer of Pluto. They were Clyde Tombaugh and his brother. The Tombaugh brothers both had a fire that burned bright inside. The brother took a chemistry study section under me in which he worked all the problems out with logarithms to 7 decimal places.

DeVorkin:

What kind of interest in physics were you developing, and who were you studying with?

Strong:

Firstly, I had taken all the physics courses offered at Kansas. I had always been interested in the laboratory. I could tell you some interesting stories about Kansas, because Kansas is the place that built a fire inside me. And when I went to Michigan, I had already had some experience growing large crystals of copper sulphate and roschelle salt (for no good reason except for the fun and beauty of it).

DeVorkin:

You were interested in radio from the beginning. Does that mean you were interested in electronics?

Strong:

No. I'm very weak in electronics. But at Kansas, I had made a very simple Geiger counter. It consisted of a brass cylinder with a phonograph needle sticking through the end of a glass tube at its center. The needle connected to the inner side of a Leyden jar; the cylinder was grounded through headphones to the outer side of the jar. On charge by means of a Wimhurst machine after the needle discharges the jar automatically to the right potential, this setup counts alpha, beta and gamma particles. It works for a fraction of a minute. My first paper was with Professor Cady on that. I had read about this counter in a German journal. I made it at Kansas, and it worked. Prof. Cady and I had a lot of fun with it. The associated "electronics" amplifier represents the major part of my total involvement in electronics.

DeVorkin:

That was "Broadcasting the Sounds of Atoms" in 1926. Very good.

Strong:

That's right. We finally put it on the University of Kansas radio, so people could hear the sounds of atoms.

DeVorkin:

Marvelous. That's quite delightful. What were your courses in physics at Michigan like, and when were you sure that you were specializing in something? What was your specialty?

Strong:

The reason I told you about the crystal growing is that when I went to Michigan they had a graduate student — whose name I've forgotten, who was trying to grow large alkali-halide crystals for infrared use. I asked Professor Randall, who was the head of the department and who was an infrared spectroscopist, if I could take on this program of growing large crystals. The chap who had been running it had left. Randall said "Yes." and by 1929 I was growing large potassium bromide crystals for infrared prisms. The significance is that earned me a National Research Fellowship.

DeVorkin:

At Cal Tech?

Strong:

At Cal Tech.

DeVorkin:

What was your thesis on? Was it on spectroscopy?

Strong:

My thesis described the growing of alkali-halide crystals for infrared prisms; the first infrared spectrometer recording. That spectrometer had a KBr prism made from one of my own crystals. The prism allowed extension of the observable infrared spectrum from wavelength 14 mu — the limit for prisms made there-to-fore from natural NaCl cyrstals — by over 12 mu — to wavelength 26 mu. The summer after my 1930 (June) PhD I recorded for the first time, the full extent of the 15 mu band Of C02 — with rotation lines resolved.

DeVorkin:

In December 1930 in the PHYSICAL REVIEW there's a paper by you, "A Method For Growing Large Crystals of the Alkali-halides."

Strong:

Yes, that's it. There's an interesting story about that. You know scientists get into little quarrels. Prof. Stockbarger at MIT grew crystals and published a paper some six years after I published mine in the PHYSICAL REVIEW. He grew his crystals the same way I grew mine, with one exception: I moved the melting temperature isotherm through the molten salt; he moved the molten salt through the melting temperature isotherm. When Stockbarger published an account of his crystal growing he wrote that large crystals of KBr were now available in optical quality for the first time. I protested to this claim by sending him a reprint of my Physical Review paper. He wrote and pointed out that I said I could do it, not that I had done it. The irony of this was that my crystals were far superior to his: For a year or so after that exchange of correspondence the KBr prism blanks supplied by Harsham Chemical Company (made under Stockbarger's patent) had an absorption band around 10 mu. I attribute this to tracers of KBrO3 — my crystals were grown in an iron pot under hydrogen — his in a platinum pot under oxidizing air.

DeVorkin:

You had grown them?

Strong:

I had grown them and they were completely free from annoying absorption bands due to the prism itself.

DeVorkin:

Oh my. So you were firmly in laboratory techniques and infrared while at Michigan.

Strong:

Sure.

DeVorkin:

You had no contact at that time with Coblentz from the National Bureau of Standards or others who did infrared work?

Strong:

No.

DeVorkin:

Okay. Let's move on to the period at Cal Tech, 1930 to 1937. You said you had an NRC Fellowship to go to Cal Tech, and this was to do specifically what?

Strong:

Well, I had a fellowship to go to Berlin and study under Prof. Czerny, a famous Berlin infrared spectroscopist. However, my wife became pregnant. Fearing that there wouldn't be any good obstetricians there, I asked the Fellowship Board if I could go somewhere else in the USA. They said I could go any place I pleased — except I couldn't stay at Michigan. So I asked Cal Tech if I could come there and they said yes.

DeVorkin:

Where did you meet your wife?

Strong:

At Kansas University. I got married in 1928. That was two years before I got my doctor's degree.

DeVorkin:

Then she went with you first to Michigan, then to Cal Tech?

Strong:

Yes.

DeVorkin:

You went to the physics department at Cal Tech?

Strong:

Yes. I applied and they assented.

DeVorkin:

What were your first duties there and what was the atmosphere like there for research?

Strong:

The atmosphere was marvelous — even the sky then, in Pasadena, was free of smog. As an NRC fellow I had no duties. I could have taught a class but I didn't. To make things coherent, I must tell how I got vectored into the aluminizing of astronomical mirrors. It owed to the circumstances that I wanted to deposit a reflective coating on the back face of the Littrow prism of my Michigan PhD spectrometer. Of course a KBr prism couldn't be silvered by the Brashear water-solution process.

DeVorkin:

You wanted to silver the back of the prism because the Littrow goes through the prism twice? And because an auxiliary mirror can't be perfectly aligned?

Strong:

Yes. Just at the time I had this requirement, a fortunate event occurred. Prof. Ornstein, from Holland, came and gave a physics lecture at which he described a procedure of evaporating silver in vacuum. It consisted of putting a silver wire in a tungsten helix and heating it. The evaporated silver condensed on the surfaces exposed to the rays of evaporated silver atoms. Condensed, they formed a mirror. I hurried to ask Professor Randall if I could set up this procedure. He said, he had already given permission to Professor Barker. But after a few weeks Barker had done nothing about it, so Randall reversed himself and said, "Yes" After I coated my Littrow prism I did nothing more with thermal evaporation there. When I got to Cal Tech, the first thing I did was design an infrared spectrometer (which was built for me). While I was waiting for it to be built, Hawley Cartwright became fascinated by the vacuum silvering process that I told him about. Together, he and I built a thermal evaporation apparatus. With it we tested evaporation possibilities — "animal, vegetable and mineral" — so to speak. With aluminum we were unsuccessful since the molten aluminum dissolved the tungsten heater wire before any mirror deposit formed.

DeVorkin:

So that was right when you got to Cal Tech in 1930.

Strong:

Yes. We published the results of these experiments. Later Cartwright left on a CRB Fellowship, for Belgium. I must have sensed the importance of aluminum because I found it's reflectivity was superior to silver in the ultraviolet. I persisted in trying to evaporate it. I indulged a heroic attempt: I fused Ti02 for crucibles to heat the aluminum in, but they were unsuccessful. Finally in 1932, it occurred to me to try heavier tungsten wire. It turns out that tungsten has a limited solubility in molten aluminum, and so the heavier wire worked.

DeVorkin:

It took more current, but you had plenty of that.

Strong:

Yes. It required a step down transformer. That was in the summer 1932. It was during the Depression and at the time I was looking forward to the responsibility for a wife and a child with no job.

DeVorkin:

Was the NRC Fellowship for two years?

Strong:

They were for one year but they regularly renewed them for a second year. After that they didn't renew them any more.

DeVorkin:

That's right. So at the end of your second year, you had perfected the aluminum process, and you were looking for a job.

Strong:

Yes. I looked for a job, but I never got any offer. The registrar there, Prof. Philip Fogg, had made a six inch diameter, amateur telescope mirror himself which I aluminized. That was the first astronomical mirror that was ever aluminized. It's now down in Memphis, Tennessee, in a museum at Rhodes College.

DeVorkin:

In the museum there? It's safe?

Strong:

They have a museum in the physics building.

DeVorkin:

How did it get to Memphis, Tennessee?

Strong:

I had a graduate student who became the head of the department there. He set up a room which he calls the John Donovan Strong Room — a little museum in my honor — I sent him that mirror for it. First of all I had to write for it to Phil Fogg (who was then chairman of Bell and Howell Co.). I told him I wanted that mirror. So he went up in his attic and found it and sent it to me. I then sent it to Memphis. Today it still has its original aluminum coating.

DeVorkin:

Marvelous, that's just marvelous. When did you perceive the advantages of aluminizing over silvering?

Strong:

I perceived the advantages before I could do it. Aluminum had a known high ultraviolet reflectivity where silver had a blind spot — around 3150 angstroms.

DeVorkin:

So that was the primary motivation for aluminization?

Strong:

Yes, that and the opportunity I saw in it to drum up a job, In which I had the cooperation of Professor Fogg. He went with me, taking his aluminized mirror along, to see Dr. John Anderson who was chairman of the 200-inch Observatory Council. Together, we sold the idea of aluminizing astronomical mirrors to him. At that point, I must have been relaxed for I did an imprudent thing: I hadn't had a vacation since married. I took my wife and daughter, job or not, for two weeks camping on the seashore at Morro Bay (near Lompoc, Cal.). When I got back to Cal Tech I met Dr. Millikan in the hall of Bridge Laboratory and he told me that I had been appointed to an Astrophysics Fellowship (paid $2.000 a year). I was delighted.

DeVorkin:

I see. Were you aware of Millikan's cosmic ray work?

Strong:

Oh my yes! I shared a laboratory room with Victor Neher. It was Neher's data that fueled the controversy.

DeVorkin:

I think that's pretty well appreciated. But at that time, of course, there was the controversy over the nature of the cosmic rays, whether they were electromagnetic or —

Strong:

We took Victor and Sarah down to the San Pedro harbor to put them on the boat to start their trip south for his cosmic ray studies. Just as the boat was leaving, Victor yelled to me, "John, I forgot to bring my developing can." He had a little can to develop the motion picture film record of the electroscope responses of the electroscope he was taking down to South America to Lake Titicaca to put it down in the lake. He asked me to mail it (airmail) to him in care of this boat at Mazetlan, Mexico. So we were buddies in the laboratory. Back at the laboratory I found the developing can, packed it up, took it over to the Cal Tech post office and mailed it, charged to Millikan. That occurred during the Depression. It wasn't long until I got a call from the Cal Tech treasurer. He said, "You know, you've spent $11 on postage. what's the explanation of this, John?" I told him that Millikan's expedition to Lake Titicaca was in hazard and this was to allay the hazard.

DeVorkin:

That's good. What were your own personal feelings about the nature of cosmic rays? Did you think about it at that time?

Strong:

Oh no. I didn't think about it.

DeVorkin:

Taking a part in building the 200-inch must have been quite a challenge and quite an interesting thing to do. What was your reaction to that? Was that stated as the purpose of your fellowship?

Strong:

My charge was to do anything I pleased to develop the instrumentation for the 200-inch telescope. But the implied responsibility was to develop aluminizing, which I did.They kind of looked on me at the time as the fair haired boy. That's the reason I got an invitation to go down and work with Dr. Hale in his private observatory.

DeVorkin:

Down in San Marino?

Strong:

Down in San Marino.

DeVorkin:

Tell me a little bit about the people you worked with, and whether there was any resistance by the older astronomers to the aluminizing process. Were they worried?

Strong:

Oh no. There was absolutely no resistance. No trouble whatever. As a matter of fact, I worked very closely with them through Milton Humason. The name probably is familiar to you.

DeVorkin:

Oh yes.

Strong:

He was, in effect, the "liaison officer" that brought the wild man into the observatory — me being the wild man.

DeVorkin:

Why were you nicknamed the wild man?

Strong:

Oh. I wasn't nicknamed the wild man. But you know, once when I was at Mt. Wilson I charged Dr. Hubble that, "The conversations at the (Monestary) table are very boring — all the talk is about what the seeing was last night; and how to develop a photographic plate." Perhaps it was roughness more than wildness.

DeVorkin:

This is at the Monastery Table?

Strong:

Yes. You know, people who are that forthright aren't typical of astronomers. Astronomers are very sedate and regulated people.

DeVorkin:

Did Hubble have any memorable reactions to you regarding that?

Strong:

Oh no. I love Hubble. Hubble was, you know, a gentleman, a gentleman is charitable. I am certain he liked me. I had very cordial relations with him. As an example of how the astronomers had to put up with me I can cite: When I aluminized the 100-inch mirror the first time, an assemblage of dignitaries appeared on the mountain: Dr. Adams, the Director; Mr. Vorella of the Carnegie Institution from Washington; my boss, John Anderson; Al Whitford and Dr. Stebbins; etc. etc. Dr. Adams asked me when I intended to do the evaporation. The tank had been pumped out all night. I told him 11 a.m. When the entourage came into the 100-inch Dome at that time I had finished the evaporation: I had let air into the tank; and it had been opened. I simply had to avoid too close surveillance.

DeVorkin:

Did you supervise the design and construction of the vacuum chamber itself?

Strong:

Certainly.

DeVorkin:

Was there any problem with building that big vacuum chamber?

Strong:

Certainly. Engineers designed it to my specification. But I was worried. I certainly didn't want the chamber to collapse under vacuum. In construction, the welding had left a flat spot in the cylindrical side wall, this worried me, so I suggested to the Machine Shop Superintendent, Mickey Sherbourne, that we load the top of the tank with sand bags to test it. He got a long wooden 4x4 from the pattern shop lumber stock and, with the tank under vacuum, he and another ran and rammed the flat spot — like attacking a medieval gate. It didn't fail and Mickey turned to me and said." "Forget it John, it won't collapse."

DeVorkin:

That's marvelous. That's a great attitude. Well, the first aluminization was apparently a success. When was that, what year?

Strong:

February in the year 1934.

DeVorkin:

1934. And this was in anticipation of designing even larger tanks for the 200-inch and that sort of thing?

Strong:

Yes.

DeVorkin:

How much was actually evaporated on the 100-inch?

Strong:

A length of about 10 cm of aluminum wire of 1mm diameter.

DeVorkin:

Okay, it's very very small.

Strong:

Very small. When the first aluminum coating was deposited, in winter. a moth miller got into the tank somehow. In the pump-down, overnight, it perished, of course. It's body lay on the 100-inch mirror face during the evaporation so that, for seven years, the mirror coating had the silhouette of that moth on its face!

DeVorkin:

Did anybody ever take a picture of that?

Strong:

I don't recall.

DeVorkin:

We were talking about aluminizing the 100-inch. What else were you doing in these years as a fellow? Because I see you were continuing to work with people such as Randall on infrared spectrometers.

Strong:

You are referring to publications that came from the earlier Michigan work. At Cal Tech I continued working in infrared.

DeVorkin:

That's right, and I was wondering, did you have contact with Petit and with Nicholson when you were working in the infrared?

Strong:

Oh yes.

DeVorkin:

Could you tell me about your contact with them?

Strong:

Petit, of course, was not a chummy type of person. Both Petit and I were involved in the design, construction, and use of radiation thermocouples. I can't remember ever talking shop with him, or with Nicholson in the 1930's. Over a decade later, when I brought Prof. William Sinton — then my graduate student — to Mt. Wilson to observe Venus and Mars with the telescope, Nicholson asked me what we were going to do about the moon. I told him we had no plans. He said that was a mistake since focusing the moon on a thermal detector was invariably interesting. So when we were ready for the planets with our spectrometer slit at the 100-inch Coude focus we noticed the moon near the meridian in late afternoon when the dome was opened to equalize temperatures inside and out. Sinton and I looked at each other and set to work to take a scan across the moon terminator — before supper, and before night work began. We mounted a Leica camera next to the slit and took periodic pictures during the scan for documentation. We only made one scan. Back in Baltimore we appealed to Dr. Fred Wright, a lunar astronomer, for a map or picture of the moon which would serve to identify our Leica photographs — and through that, the path of our scan. That scan is reported in Sinton's dissertation. It passed, by pure chance (we told ourselves) exactly across the newly christened Crater Porter.

DeVorkin:

Russell W. Porter?

Strong:

Yes. Russell Porter himself. A crater on the moon had been named after him.

DeVorkin:

You must have met him when you were involved in the 200-inch project.

Strong:

Yes. We saw a lot of each other. With Russell Porter a group of us organized a club. We called it the "100 to 1 Shot Club." We met at various member's houses at Palomar; in the Mohave Desert; etc. — about 6 or 7 times a year. It was called by the name mentioned to indicate that our considerations (like: Does the water spin in a contrary way in the Southern hemisphere when it runs out of the bath tub? — etc.) were restricted to topics that were fantastic by a factor of 100:1 over scientific. The dozen members included: Trim Barkelov — patent council for Paramount Pictures Roger Hayward — artist and architect Victor Neher  laboratory roommate George Mitchell — millionaire manufacturer of the Mitchell camera; a former Hollywood camera man Byron Graves — an amateur astronomer and retired executive from Ford Co. in Detroit John Anderson — my boss Jack McMorris — a chemist (and disappointed concert pianist) George Worrell — successor to Mitchell at the Camera plant Milton Humason — astronomer I mention this because it was a group worthy to go down in history. On one of his earlier Arctic expeditions Porter had composed some piano music which his wife, Alice, had discovered in the attic. Without telling him she gave it to Jack McMorris who in turn had a local concert pianist, Lillian Stuber, play it for a disc recording. Then at Jack's house, on the occasion of a Sunday morning 100-to-1 Shot breakfast meeting Jack surprised Russell by playing it. We all knew what was up. Russell recognized it at once.

DeVorkin:

Marvelous. What was his design style? What was his role in designing the 200-inch?

Strong:

Porter's most conspicuous, and I would say most important role, was interpretive: He could look at the drawings and designs of the engineers. (Fasserro, Surrerier, and the others) and then make a pencil drawing that appeared as if the component involved had already been built, and photographed. These previews were of value to the Observatory Council, obviously, and they were, in addition, works of art.

DeVorkin:

I see. Very interesting. So that was a very important role for him.

Strong:

He played a very important role. I cannot give you an example of his participation in original design. I'm sure he contributed much.

DeVorkin:

I see. Did he ever create pictures that you know of — images, treatments — that showed the Council something they didn't want so a design was changed as a result?

Strong:

I suppose so — but I cannot give an example.

DeVorkin:

Okay. What about the small site testing telescopes that he designed? Are you familiar with those at all?

Strong:

I have one of them.

DeVorkin:

You do?

Strong:

Dr. John Anderson gave me one of them. They were of one meter focal length and they mounted on a firm tripod pointed at Polaris. The observer counted the number of discernable diffraction rings around the Polaris image as a measure of "seeing".

DeVorkin:

Right. Where do you have this telescope?

Strong:

When I settled at Hopkins, a lot of things got sent from Cal Tech. Jesse Greenstein asked me once if there was anything else I wanted, and I told him I wanted a certain quartz photo cell. It was made by electrolyzing sodium through glass. I didn't have the wit to ask for the Leica camera that I had had there — He would have given it to me. It was the first camera to have its lenses coated with a film of MgF2 — a reflection reducing film. I coated its lens surfaces.

DeVorkin:

I see. So you took these things to Johns Hopkins?

Strong:

I took them to Johns Hopkins and it included one of the site telescopes.

DeVorkin:

And is it still there or did you bring it with you here to Amherst?

Strong:

I brought it here to Amherst, but I'm not sure I could put my hands on it at the lab. I looked for it a few years ago, and I think somebody must have stolen it.

DeVorkin:

Oh my. But the possibility is that it's around here somewhere?

Strong:

There's a possibility that it's around here.

DeVorkin:

Not in your house here?

Strong:

Not in the house, no. If you ever want it for any purpose, I'd have a thorough search made for it.

DeVorkin:

Yes, I think we would. We would like to know about it and I'm sure that the museum would be very interested.

Strong:

I think that there was a total of ten of them that were built.

DeVorkin:

It's a very important piece of history. Let me ask you about the people that you worked with.

Strong:

I will first speak of my boss. John Anderson: He supervised construction (optical and mechanical). But he never ceased being a natural physicist — with his little private projects — quietly pursued. One of these was the study of "seeing". He devised a novel way to evaluate it. A large part of the optical distortion of star images — the scintillaton, etc. — is produced in the stratosphere (as Douglas showed). Dr. Anderson made a pocket telescope about the size of a large fountain pen... it had an object lens at one end, and an eye lens at the other. He would hold the eye-lens end of the telescope to his eye with his left hand and move the objective end of it, with his right, in a small circular path at a "standardized" frequency. The image of a bright star (usually one low in the western sky) appeared, like a 4th of July sparkler moving in circular path, a circle. And the scintillations punctuated the circle so it looked like a beautiful necklace of pearl beads. Dr. Anderson simply estimated the number of beads in a convenient sector of the cirle to give him the frequency of scintillation. A high frequency of (as I remember) 50 cycles per second meant poor seeing — a lower frequency, good seeing. Another one of these little projects of his was the calcite achromat. He discovered that the partial dispersions of the ordinary and extra-ordinary rays for calcite satisfied the condition for making an achromatic doublet. The resulting lens gave two polarized images. The poor image in the orthoginal polarization was blocked with a paddle. For the good image the transmission, and correction extends into the ultraviolet. Its performance is described in my optics book.

DeVorkin:

Well, I first heard of Anderson when he worked with Pease and with Michelson in 1920 on the big interferometer for the 100-inch telescope, he always seemed to be the real problem solver.

Strong:

Oh. he was. He was.

DeVorkin:

What was his actual role in the 200-inch project?

Strong:

He was chariman of the Executive Council.

DeVorkin:

What did that mean he was responsible for?

Strong:

One of his important accomplishments was a test lens, for testing the 200-inch parabola in the Pasadena Optical Shop. As Gaviola has shown, the knife-edge test at the center of curvature of a parabolic mirror is faulted by the fact that pheriferal rays focus at different distances — a situation not found in the knife-edge test of a spherical mirror. Dr. Anderson designed and built an aspheric lens of about 1 foot in diameter. When it was properly located in front of the knife-edge it caused the parabola to look like a sphere. He also, applied Gavola's knife-edge test procedure. Quite apart from his 200-inch role, Dr. Anderson had produced the highest temperature on earth until the atom bomb — 20,0000 degrees. And, he did it in his characteristic, simple way. He simply made a saw cut in a 1-inch cube of wood strung a very fine wire along near the bottom of the cut and then exploded the wire with the discharge from a bank of charged condensers. It was a large bank that had a volume comparable to the volume of this room. The exploding wire was focused on the slit of a spectrograph and the spectrum yielded the temperature. It amounted to simulation of a blue-star's spectrum. Dr. Anderson was a very quiet person. I do not think he published about his calcite lens, etc. He had an enormous and pragmatic creativity coupled with very sound judgement. If there was a defect in him it was perhaps marked when an ex-captain from the Navy was brought in to move things faster on the operational side.

DeVorkin:

Did Anderson have trouble monitoring the shops and managing the project?

Strong:

No. No. Everyone trusted him.

DeVorkin:

Was he interested in doing any specific scientific projects as well?

Strong:

I think, vis-a-vis the 200-inch project, that he took objective stance — as an obligation of his executive position.

DeVorkin:

Okay. He did a broad number of things.

Strong:

You know his history at Hopkins, don't you?

DeVorkin:

No. I don't. I'd like to know that.

Strong:

Hopkins was where he got his doctorate. He came there from a little college near Chicago called Valparaiso College, and the only telescope held ever looked through was the refractor telescope there — having a lens with an aperture of about three inches. When he came down to Hopkins with its Alvin Clark 9-inch telescope he was impressed. After Rowland died the ruling of gratings languished until Prof. Ames put Anderson in charge of the ruling engines. The reason that he went to Mt. Wilson was that Dr. Hale enlisted him to make a ruling engine at the Mt. Wilson laboratory.

DeVorkin:

I see. I didn't realize that.

Strong:

That's the reason he left Hopkins. After I became a professor at Hopkins I visited Anderson, who had a very high opinion of Hopkins; and I found that he was more interested to hear about the 9-inch Avin Clark telescope at Hopkins than to report to me on the 200-inch for Palomar.

DeVorkin:

That's beautiful. In continuing, going back to infrared work in the 1930s, I know that you were doing a lot of work on evaporization processes and vacuum techniques, but you also worked on monochrometers and did some infrared work in the thirties. Did you work at all or follow the atmospheric studies, planetary studies, that Dunham and St. John and others were doing at the time?

Strong:

Oh, yes. You see, infrared got me into thermal evaporation; that got me into the aluminizing of telescopes; and telescopes coupled with my infrared got me acquainted with Nicholson and Petit. I was making my own radiation thermocouples at the time. Cartwright's dissertation was on thermocouples, and I got introduced to that art by him. I certainly read all of the Nicholson and Petit papers on the moon and on stellar radiometry. Dr. Abbott came to Mt. Wilson as a visiting astronomer and I remember making a vacuum thermocouple for him. It was provided with a KI window (out of one of my Michigan crystals). KI transmitted the infrared as last twice as far out into the long wavelength infrared as a natural rock-salt window. My crystals seemed to invite me to look at atmospheric transmission beyond the wavelength 8 to 14 mu atmospheric window — and I made observations in Pasadena, and at Palomar. I used a home-made radiometer using residual rays of crystals to isolate various spectral bands. Indeed, it was that work which got me into military research during WWII. I think, also, that your Smithsonian scientist, Fowle, inspired me to study atmospheric transmission — I saw an opportunity to extend his work. Laboratory studies of the transmission were also stimulated when Dr. Walter Elsasser came to Cal Tech. I have had great privileges having known Abbot and Hale. Millikan and Michelson, R.W. Wood and Lyman, and of course, all the 1930 California astronomers, particularly Dr. Wright of Lick. And C.P. Butler, one of Abbot's men on the solar constant, worked with me during WWII.

DeVorkin:

My interest in that work in the late thirties, when you were determining the height of the ozone layer, was that eventually studying the ozone layer was done in great detail with rockets. What was your interest in determining the height of the ozone layer in 1939 and 1940?

Strong:

The 9.6 mu atmospheric absorption band of ozone lies in the shortwavelength half of the 8 to 14 mu atmospheric window. I had measured the pressure dependence of its absorption in the laboratory. I did this with Martin Sommerfield who used the results as the subject for his PhD dissertation. A critical factor was the opportunity to involve K. Watanabe, a post-doc fellow in the ozone height project.

DeVorkin:

Could you tell me a little more about Keniche Watanabe, because he went to NRL during the war and worked with Tousey, and they did determine the height of the ozone layer by traveling through it with V-2 rockets. I'd be very interested to know more about Watanabe, especially as he was interested in photoelectric work instead of photographic.

Strong:

The ozone absorption coefficients in the centers of it's (infrared vibration) rotation lines are Strong. Thus, the pressure-broadened, wider lines at the bottom of the ozone layer take the narrower lines above out of play. The overall transmission of the 9.6 mu band is heavily weighed by the pressure broadening at the bottom of the layer so that the height yielded looses meaning. Cambridge University was attracted to our method and they set it up for observations that lasted a year or so. The results for the height were consistently too low.

DeVorkin:

Well, tell me a little more about Keniche Watanabe. Where did he get his degree and what kind of a person was he?

Strong:

He got his degree at Cal Tech. He was a quiet and retiring sort of fellow; but the most effective teacher I ever knew. For example, the Cal Tech freshman class of 160 was selected by personal interviews from 250 candidates that had passed the entrance examination. Further tests after they arrived on campus in the fall allowed a segregation of the 20 potentially smartest into Section A — a section taught by Prof. Watson; the 20 next most promising into Section B — taught by Strong; and six unsegregated sections of the remainder — one of these being concurrently, taught by Watanabe as a graduate-student instructor. When an examination was given, each of the 8 teachers of the 8 sections provided one question which he graded for the whole freshman class of 160. Thus, the grades had high consistency, from section to section: The grades of Section A were, as I remember 85 and up; Section B were 75 and up; and of the six others, with one exception, 75 and down. That exception was Watanabe's section which was always a close competitor for second place with my Section B. I don't know how he did it. The circumstances that made his work with me possible grew from a neutral-density, platinum filter that I made for Dr. Walter Baade (Mt. Wilson astronomer). It provided the opportunity for me to get Dr. Watanabe as a post-doc associate.

That filter served in Dr. Baade's study of stellar magnitudes on classes that led to his discovery of Population II stars. He wanted a neutral density coat over one half the area of a 4x5 inch cover plate — to cover his photographic plate. If the (platinum) filter reduced the photographic exposure by one magnitude then two stars that appeared equally exposed in the two halves of his star field would be of 1 magnitude difference. It became a "break-through" in stellar magnitude precision. Thermal evaluation of platinum is difficult to control. Dr. Baade told me the filter didn't either need to be uniform, or exactly one magnitude in attenuation. But when I got into it I decided to do it well; and I don't think he had to involve any calibration corrections. He was delighted with the filter. Whenever he gave a paper on his results there was occasionally an astronomer who would want such a filter, since it provided a good observing program. This brought filter requests to me. But, I had had my fill with Baade's, so I never made any more of them. Watanabe came into the picture when I asked Max Mason for a post-doc fellowship for him. Apparently the filter-frustrated astronomers had been complaining to Mason that if Cal Tech got 6 million they should benefit from it by one filter. Mason asked if I might with Watanabe's assistance, be able to make a few more filters. I said "Yes"; but I'm afraid I never did even though I did get the post-doc fellowship for Watanabe.

DeVorkin:

What were his personal interests in physics? What did he want to do?

Strong:

I cannot tell you what his scientific motivations were. Our relations were pleasant, and he was as effective with me as at teaching. After Watanabe became professor in Hawaii, he sent Hjami Sakai, his student and co-worker to Hopkins to work with me for his PhD. Now Sakai is a tenured Profesor here. I brought him in when I retired, as my successor.

DeVorkin:

Okay. The reason I'm interested in Watanabe is that he went to NRL and he worked with Tousey, and then after that, he went to AFCRL and helped to pioneer the tungsten cathode techniques for photoelectric spectrometers that were flown in rockets. I had the feeling that Tousey was not interested in photoelectric work but rather in photographic, and I'm wondering if Watanabe left because of that reason, or if there were other reasons.

Strong:

I can't tell you. Watanabe had a typically Japanese personality – non-committal about his own affairs.

DeVorkin:

The last question then on Watanabe is about the ozone work. Now, he worked on the pressure effect with you. Was he interested in geophysical measurements as well, or was he purely a lab physicist in his interests?

Strong:

Well, he joined me because I propositioned him and it was an opportunity for him. I don't think he was extraordinarily interested in the ozone geophysically. I don't know much about his motivation. With me that was adequate.

DeVorkin:

Let's move on then. Is there anything else about the 200- inch telescope project we should talk about, your involvement, your work?

Strong:

I can't think of anything. Don Hendrix, the optician who figured the 120-inch for Mt. Hamilton. also finished the figuring of the 200-inch. And he became my successor at aluminizing. The picture of me with the 200-inch freshly aluminized also includes Don Hendrix since he was with me in doing it. That was in 1947.

DeVorkin:

Did you have any contact with Babcock?

Strong:

Certainly.

DeVorkin:

Was this your first contact with making gratings and working on ruling engines?

Strong:

I had many conversations with the elder Babcock. We naturally liked each other. He ruled the first grating on an aluminized glass surface for me. I appealed to him after Julius Pierson at Cal Tech had tried it. Julius told me, "The aluminum dissolved the diamond." I'm not certain that the Babcock son was then involved with the ruling of gratings. I remember that he was interested in automatic guiding (in about 1941 — maybe 1947).

DeVorkin:

Was this after you were back at Johns Hopkins?

Strong:

Oh no. The first ruling on an aluminum film was while I was still at Cal Tech. The time was about 1936.

DeVorkin:

So you started ruling when you were at Cal Tech?

Strong:

No, no I only initiated the aluminizing of glass grating blanks. The grating's were ruled in it by Babcock.

Strong:

There is an incident I would like to recall. It bears on Dr. Anderson's attitude toward research. My 1932 Fellowship charge was to do anything that would improve instrumentation for astronomers. Accordingly. I thought of image intensification. I assessed the possibility of focusing a star field on a transparent photo-cathode. Accelerating and focusing the photo-electrons emitted beyond the cathode on a photographic plate — accelerating them with an electric field; and focusing them with a magnetic lens — I looked up the cogent photo-electric efficiency and the photographic effectiveness of accelerated electrons. The result was a promised, substantial intensification. I approached Dr. Anderson with this idea. He was enthusiastic about it and said "Do it". I explained that I needed to finish my literature search. His repsonse was that I had better start to do it, that any further literature searching would simply convince me that the idea wouldn't work. Unfortunately, other matters interceded and I never did "do it."

DeVorkin:

This was in the early thirties?

Strong:

Yes, It was 1932 or 1933. That was before image intensifier tubes came in.

DeVorkin:

That's marvelous. That is really a very interesting recollection, because he was the sort of fellow who seemed to be very intuitive with what he did.

Strong:

At meetings of the 100-to-1 Shot Club, we had long conversations about ruling gratings. He told me "There are no great problems with the ruling engine screw. The main problem is to get the diamond to go back and forth in the same straight line." Anderson wrote an article on ruling engines for Glazebrook's DICTIONARY OF APPLIED PHYSICS (a beautiful set of three or four volumes). I have learned a lot of physics out of that book. Anderson in his article tells how he made cross rulings.

DeVorkin:

You said there were three things you wanted to add?

Strong:

One concerns Paul Merill — the interstellar mass astronomer. He didn't trust me at first when I propositioned him to let me aluminize his pet Hopkins grating. It was speculum metal ruling, and I told him I could increase its efficiency by 50% — from 60% to 90% surface reflectivity. He demurred at first. But when I brought him a speculum grating which I had aluminized 10 times, he gave in. One can remove the aluminum coat with a Strong caustic potash solution followed by copious washing under a tap. I coated his grating successfully — and to his great satisfaction. That's one story I wanted to tell you.

DeVorkin:

Marvelous. This must have been from the 1930s?

Strong:

Oh yes — about 1936. Of course, when I worked with Hale, he was getting the Copley Medal for his work on the magnetic field of the sun. Being a very fastidious scientist, he wanted to check the 1910 Zeeman observations of Van Maanan, Lasby, and Sears — observations that established a general magnetic field of about 10 gauss. The Zeeman line shifts produced were at most only a few thousands of the line widths on the spectrum plates. I was charged by Hale to remeasure some of the old 1910 plates with his nice new Zeiss microphotometer (it was in the basement shop of his San Marino Observatory) The old observations had shown a variation of field — with a greater field for lines considered to have a deeper origin in the sun's atmosphere. I reckoned that if the field was stronger at higher atmospheric pressures, and temperatures, then the lines should show different assymetries for the right and left circular polarizations. I got the idea of a null approach — a kind of a null measurement: My idea was to make a multitude of microphotometer traces and determine the bisector the microphotometer traces. Then all these bisectors would be brought together for the centers of each line traced, and averaged. It was expected the two averages, for She two polarizations, would then diverge progressively as the bisector represented, more and more, the line wings. Dr. Hale was pleased with my idea, and he followed my results closely. However the idea never worked out. Recently, Dr. Babcock explained "why" to me — but I can't recall the "why" now. Dr. Babcock instrumented the San Marino solar telescope to determine daily variations of the field over the suns face routinely. That observatory has coelostat mirrors that I'll never forget: when the aluminizing procedure emerged those were the first astronomical mirrors that I coated "in anger"—to use a naval term. Dr. Hale's eagerness for progress was the reason they were the first — just as for their being the first large Pyrex glass mirrors in astronomy. And being the first mirrors, they contained millions, it seemed, of tiny bubbles. Perhaps only hundreds of them were cut by the figured and polished mirror surfaces. Each bubble that touched the mirror surface had been ground out. The resulting small pits were all still filled in with polishing pitch, and rouge — from the original polishing and figuring. I remember them because, before aluminizing, I had to regrind each one to get it free of pitch — since pitch is anethema to aluminizing. There's a third story I wanted to tell: When I coated the 100-inch mirror in 1934, Dr. Adams was working on the Einstein gravitational red shift for the lines of the companion to Sirius. Since Sirius' companion is 10,000 times dimmer he had a substantial problem of correcting for scattered light. And so when I first aluminized the 100-inch mirror, and it was free of the scattered light (that comes from the necessary burnishing of silver), Dr. Adams was eager to use the aluminized mirror. The result was gratifying — so gratifying that he sent word down to me by Humason: If Strong has a problem that he wants to use the 100-inch telescope mirror on, he may have it for one night a month. That was before I had any pretensions of being an astronomer. I was only interested in the procedure of aluminizing.

DeVorkin:

Oh did you pass it up?

Strong:

Yes. I didn't have any problem that was apt for the 100-inch telescope.

DeVorkin:

Okay. Let me ask you about the writing of your book, Procedures In Experimental Physics, which first came out in 1938. You were still a fellow at Cal Tech.

Strong:

I think I had just become an assistant professor. I met Max Mason on the campus one day and told him I was planning to go to work the first of the year for Otto Beeck at Shell Development Co., Emeryville, California. Mason asked "why." I told him because I had no academic appointment; my salary was hardly a living wage; and I was tired of aluminizing mirrors for astronomers. The upshot of that was Mason's provision for an extended trip in the East, visiting laboratories at Cal Tech expense: a promised appointment; and, an escalation of my salary to $3,500. That was in 1937. I must tell you an interesting story about Max Mason, that I later came upon. Dr. Mason had been the youngest President of the Rockefeller Foundation. His first action in office there had been to push through funding for the establishment of a Mathematics Institute in Gottingen Germany (where he had gotten his Doctorate). When Dr. Mason came to Germany to inaugurate it, he paid a call on his aegis Professor, who was to be the new Institute director. It was either Courant or Hilbert, I forget. Professor Courant or Hilbert asked Mason how long he would be in town. He then explained why he would like to have him call back later. This was because he was busy finishing his speech for the inaugural, and that he was about to go to the University to meet the Rockefeller Foundation's President. Dr. Mason said, "I'm that President." Courant or Hilbert said "Oh, no! Not you Max."

DeVorkin:

What prompted you to write the textbook Procedures In Experimental Physics?

Strong:

One thing lead to another: I became a sort of "confessor" to several of the Cal Tech researchers. I was useful to them because I would listen to their experimental problems. They were useful to me because they stretched my involvement in procedures. I was familiar with earlier books on procedures, but they seemed inadequate. The opportunity to involve Roger Hayward, with his wonderful talent for illustrations, was an important factor. Russel Porter could have illustrated the book but there was less generation gap between the Strongs and the Haywards. And Hayward's architecture involvement was at low ebb due to the Depression. And there were other favorable circumstances: the opportunity to learn all the nuances of glass blowing from Clancy, the Cal Tech glass blower; of optical surface generating from Marcus Brown (working in the 200-inch optical shop) and from Don Hendrix of the Mt. Wilson Shop on Santa Barbara Street; and of learning about metal working. I have a reputation in the large community of being a good glass blower. It's a much overblown reputation — one that owes most to my effectiveness as Clancy's amenuensis. When I had the manuscript for the book almost finished, I showed it, with Hayward's drawings, to Dr. Millikan. He was himself. you know. an experimental physicist first and foremost. He was enthusiastic about my project.

DeVorkin:

So you wrote that book and it was published in 1938. You must have used it in your own coursework as you became an assistant professor at Cal Tech.

Strong:

No. it's not a textbook.

DeVorkin:

It isn't, really?

Strong:

It wasn't intended as a textbook, and has been used only a little as one. I can cite one example: Recently, a retired A.D. Little chemist told me that he got acquainted with my name when Professor Kistiakowsky at Harvard used my book in his course for chemists on experimental techniques. Its main use was as a how-to-do-it book for individuals.

DeVorkin:

Did that help you become an assistant professor?

Strong:

No. That was a result of the aluminizing. The book wasn't out then. I don't know whether Max Mason knew about it.

DeVorkin:

How did your duties change? Did your interest change as you became assistant professor at Cal Tech?

Strong:

I just wanted that title because everybody else wanted one. It didn't have any great influence on me at all.

DeVorkin:

Did you continue working on the 200-inch then?

Strong:

Oh. yes. I told you about my getting Max Mason motivated to get me the assistant professorship — I told him I had a bellyfull of aluminizing mirrors. He said, "You don't ever have to do another mirror again. John. We would like to have your advice and counsel. Nevertheless, I continued with aluminizing.

DeVorkin:

You worked on an optical slit design?

Strong:

Yes. I carried a reminder to remind me to design a slit that involved the kinematical design, in some way. I remembered the moment the idea struck. Russel Porter made an illustration for me of the design that resulted, after it was constructed. I published it. Dr. Sears of Cambridge University saw my design and called my attention to his earlier publication that showed a drawing for the same design. Even screws in his design and mine were similarly located. I was very embarassed. I knew I hadn't plagurized him because the Cal Tech Library did not take the journal he published in. It was simply that we had both sensed how the slit wanted to be designed. [Like Professor Rainich in his Michigan lectures told us repeatedly, speaking of mathematical developments: "It's like a sturgeon that likes to be cooked in sour cream."] And so I had to write a note of apology. That was the slit story.

DeVorkin:

Quite fascinating. In the early forties, as the war began first in Europe and then gradually expanded, were you concerned? Did you want to participate in some way? I know that you left in '42 for Harvard, but was that to do with the war at all?

Strong:

First of all. I must confess that I was an ardent isolationist then — and I didn't have any urge to run down and enlist. Two factors came into play. I had been observing infrared transmission of the atmosphere and I had observed that the 8 to 14 mu atmospheric window was not blocked by the smoke from orange grove smoke pots when that made the sky black in Pasadena when a freeze threatened the fruit. Also, on Palomar, I had found those wavelengths from the sun penetrated to my apparatus through haze when it was dense enough to make the disk of the sun blur out. I believe Max Mason knew of this, and that he told on me (to the military). Another factor was that Alan Bemis, at MIT, was working on a target-seeking, dirigable bomb. He asked me to come to Harvard and collaborate with his MIT project. I told Max Mason he could draw that project out to Cal Tech if he would — I told him that we were ahead of the Bemis group as far as detectors and knowledge of infrared was concerned. Dr. Mason said he would try. Alan Bemis was scheduled to call on me the next morning at 8 a.m. I asked Dr. Mason to join us in my Astrophysics Bldg. office. He agreed. At 8 a.m. Mason didn't show up. Neither had Bemis. I ran up the stairs to Dr. Mason's 3rd floor office and found that he wasn't in. After waiting a while for him I ran back down stairs. Just then Bemis arrived. So I agreed to go to Harvard. Later that day, when I saw Dr. Mason he asked, "Where were you this morning at 8?" It turned out he had come down to my office from his the same time I had gone up from mine, vice and versa. We missed each other because he took the elevator while I took to the stairs. That is the story of my transfer to Harvard for war effort work.

DeVorkin:

So without Max Mason there, you couldn't argue to move the project to Cal Tech?

Strong:

No.

DeVorkin:

That's too bad. Or was it too bad?

Strong:

I don't think it was too bad.

DeVorkin:

What was your experience like at Harvard? You worked in the physics department?

Strong:

Yes, on the top floor of Cruft Laboratory.

DeVorkin:

And your work there was on transmission effects?

Strong:

We had a field laboratory — a small building set up at Fort Heath. It tested the atmospheric transmission across Round Bay — between the receiver station at Ft. Heath and a source of infrared radiation that we set up on the tip of the Nahant peninsula. The British, when they saw our set-up, liked it well enough to copy: they established a similar set-up at Castle Tantallon in Scotland. In the Cruft laboratory we had a laboratory where we worked on detectors. At Cruft, we were behind an iron gate on the top floor of the building. Once I got a visit authorization from a Dr. Randall of St. Andrews College, Scotland. At the gate, when he called, as I admitted him I remarked, "Since you come from St. Andrews, I surmise you have heard of my golf game, and have come to talk about golf?" "No". he said quite seriously, "I come to discuss thermal detectors with you." So we talked shop. After the war I got a British journal that showed his picture on the front cover. He may have been knighted in recognition of his having invented the strapped magnetron (for radar). I soon got into trouble at Harvard. I reckoned that I could make a passive infrared range finder for ships at sea working from their infrared emission. I found the NDRC personality above us was not enthusiastic. That was Dr. Duffendack. So. I told the Navy, at the Bureau of Ordinance about my idea, and they supported it. Finally, when the idea got embodied in hardware an official test of it was planned. The test was to be attended by the "brass" — Lieutenant Commanders from the Navy and Colonels from the Army. We arranged to have a tug boat in Round Bay to serve as our target ship. It was to follow a course in Round Bay and we were to range it — both by means of a 1-meter-base, visual range finder at Ft. Heath, and with our new infrared job. Preston Butler was to be aboard the tug. He was a former Smithsonian observer of the Solar Constant for Dr. Abbot. Jim Hooper (another of our group of 4) was to man the visual range finder at Ft. Heath. Jim knew the Morse Code, and Butler learned it (in 2 weeks) so that the two could communicate by blinker lights. Jim Winget manned our infrared range finder I was to give the "brass" a briefing while the other three of our group got the show going. We had been bothered by one problem — a sporadic noise that crippled the electronics. We had located it in necessary slip rings; and we had seven cures when the ailment arose. Often none was an effective cure. Sometimes one, then another. The apparatus at times even cured itself. It was a great worry for us — would we be free of it the night of the demonstration? While I was giving the briefing that night, we had the arrangment that Winget, outside with the gear, should periodically come to a window to signal to me: Fingers in his ears meant electronic noise. A finger on his lips meant the noise was satisfactorily quiet. As I gave the briefing he repeatedly gave me the report I rued — but I persisted with my briefing. Just as I was finishing the briefing he showed up at the window with his finger on his lips. That was 9 p.m. We demonstrated without noise, and we ranged all evening to 5% or less. Finally, when everyone was leaving, satisfied at about 11 p.m.. the noise reappeared. It seemed that we certainly must have been living right.

DeVorkin:

Was that range finder put into operation?

Strong:

The Navy gave a contract for its development but I understand it wasn't finished in time for WWII.

DeVorkin:

Tell me, what kind of detector was used?

Strong:

Metal bolometers in a surrounding of lowpressure hydrogen or helium — nickel bolometers. Prof. S.P. Langley, if he did not invent it, at least named that detector. And, he certainly pioneered it. It was not as sensitive as semi-conductor cells that have superceded it. These were first developed by the Germans. One of them was picked up by General Eisenhower's army. It came to this country and the Navy sent it to me to evaluate. At first, I took a dim view of it — it was simply a disk-cell with two electrodes on the back. However, when I substituted it for one of my own bolometers my respect was aroused. It was a hundred-fold more sensitive.

DeVorkin:

This was before Cashman was making —?

Strong:

I think it was before Cashman.

DeVorkin:

That was from Germany?

Strong:

That is the way I remember, from Germany.

DeVorkin:

When was that? Do you remember the year?

Strong:

It was, I believe, in the spring of 1945.

DeVorkin:

Well. that's very interesting. You must have been quite surprised.

Strong:

I was.

DeVorkin:

Did you apply it, work on it?

Strong:

Sure.

DeVorkin:

How did Cashman come to make these things, then?

Strong:

I am, at the moment, unable to give you any details about the early history of PbS detectors. It has always been my impression that they were introduced in Germany, and that Cashman's contributions followed. But I may be wrong.

DeVorkin:

I see. That's interesting. When you first saw this and used the lead sulfide cell, did that greatly increase your interest in doing science with infrared or what?

Strong:

I have used lead-sulfide. Lead-selenide and lead-telluride cells extensively. But at the end of WWII I was not excited by the promise of the infrared for military application: To me, the detectors (even PbS) seemed too insensitive, the military targets too weak as infrared sources, and, the background too cluttered. But cooled semiconductors cells; very hot jet engines as targets with the targets, above the background clutter of clouds soon changed all that — and so I proved me to be a poor prophet.

DeVorkin:

But you were excited about it?

Strong:

Yes. Yes.

DeVorkin:

Okay. You contined at Harvard until 1945. So you were only there for about three years. Did you have an actual faculty position at Harvard?

Strong:

Oh no. That was the whole point. Harvard asked me to stay on but it was without an academic appointment. I had, at that time, several opportunities in addition to returning to Cal Tech. These included offers of jobs from Dr. Land of Polaroid Corp and from Dr. Hulburt of NRL; also professorships: one at NY university, and the other at Michigan. Land's offer was tempting: he said I could do what I pleased in the way of research, with their support, as long as I devoted part of my time to Polaroid problems — I remember it as half time. I elected to resign from Cal Tech and go to Michigan. There, my professorship was perhaps the shortest tenure (two weeks) on record. After I got to Ann Arbor I got a call from Prof. Dieke at JHU with an offer of a professorship. Then President Bowman contacted me by phone. I always thought he was put up to it by Dr. Hulburt. I told him I couldn't come because I had told Michigan I would accept. Dr. Bowman said, "Strong, I do not think that a moral point is involved. If it is, then you are the only moral professor I know." My admiration of Professor Wood and Pfund made the offer effective — to get associated with them. The physics department of the University of Michigan had a committee to pass on professor's research. I took offense at that and resigned. The attraction was certainly not money, for my salary at Hopkins was only $6,000.00 I had at least one arrow in my quiver. The Office of Research and Invention (later ONR) had assured me that it would support my infrared work wherever I might go. When I said "Harvard no! and "Michigan yes," they said "Michigan yes". Then, when I changed my mind again they supported me at Johns Hopkins.

DeVorkin:

Who actually wanted you at Hopkins? Was it Bowman himself who wanted you?

Strong:

Well, I do not, of course, know. I think it was Pfund and Wood at first. I do know that Prof. Dick Lord (of MIT, later) mentioned my name to Pfund. I think they could not have motivated President Bowman, as he was motivated, unless my unconfirmed suspicion is true that Hulburt influenced him. One incident had impressed Prof. Pfund that I was an optics whiz. It was a lucky coincidence due to the fact that I had been reviewing polarized light. In his office once, he played a trick on me which I saw through immediately — as a result of that lucky review: He gave me what was purportedly a piece of Polaroid sheet between glass plates. He said one could rotate it and see the waxed floor get alternately bright and dark — the reflected window light was polarized on reflection by the waxed floor. He handed me the polarizer and I saw it. He took it back, and looked himself. He said "My goodness. I can't see it now." Then he handed the thing back to me and I couldn't see it either. He had on the sly, turned the plate over. I said, "You have a half wave plate on one side of the Polaroid sheet, and you turned it over." Prof. Pfund had developed a monitoring process for DuPont for making cellophane sheets of uniform thickness. It depended on the sheet being a half-wave plate. The cellophane around a package of Granger tobacco was such a half-wave "plate." Professor Pfund had put some Granger cellophane on one side of the Polaroid sheet. Prof. Wood also had a good opinion of me from our work together at Cal Tech on anomolies in grating spectra. Also, he had adapted the aluminizing of glass grating blanks that I had introduced. I had found anomolies in the spectra of 3 gratings — one of them was the grating ruled by Babcock for me on an aluminized glass plate. I presented a paper on my results at a Berkely meeting of the physical society (circa 1937). Wood was there. After Berkeley he came to Pasadena for a couple of weeks during which we experimented together on grating anomalies. He had encountered them many years earlier, and Lord Rayleigh had proposed a formula that predicted where they occur in spectrum. When Wood returned to Baltimore I divided the Babcock ruling into two pieces, and gave one to him so that he could continue experiments in Baltimore. Enrique Gaviola, from Argentina, was then working with me at Cal Tech. He had previously spent a year with Wood in Baltimore, and he knew him well. When I gave Wood one half of my prize example of anomolies, Gaviola said it was a mistake. He said, "Wood will go back and do experiments, and describe them in such a spectacular way in a publication that your part will be lost." Actually Wood did just that; but his very impressive paper in the Physical Review gave me full credit for my work.

DeVorkin:

Good. That's marvelous. So, you were invited to Hopkins, you went to Hopkins; what did you want to do when you got there?

Strong:

At the very first I started an infrared study of atmospheric absorption, using ONR support to acquire a big tube in which I could introduce absorber gas at a variety of pressures.

DeVorkin:

The big tube being a vacuum tube?

Strong:

It's an evacuable tube: 3 feet in diameter and 100 feet long. Two 3-foot mirrors make a Pfund-type absorption cell of it that affords an optical path 300 feet long (3 passes) or, 600 feet if double passed.

DeVorkin:

This was primarily for ONR, Office of Naval Research?

Strong:

Yes.

DeVorkin:

You also worked on ruling engines and gratings. Did that activity increase?

Strong:

When I first went to Hopkins, Prof. Pfund was head of the department. He influenced the local power structure in such a way that they asked me to take charge of the ruling engines.

DeVorkin:

Did you want to do that?

Strong:

I wanted it to get involved with gratings, but not to get myself crossed up with Prof. Wood, or with Prof. Dieke. I knew that Wood was ungovernable, and that Dieke enjoyed the control over the distribution of gratings to other spectroscopists. I responded with a counter proposal, that the engines be managed by a committee of three. It amounted to simply testing whether we could continue informally with several bosses for Wilbur Perry. If you knew Perry you would see that wouldn't be a problem as he would also do as he pleased. That arrangement worked well until the time that I discovered Professor Dieke showing off my work to a visitor. That seemed to me to be a trespass on my "turf." I offered him exclusive control. He countered by withdrawing from the committee. I think I asked him to continue the distributors. But, I more or less controlled the gratings production and development after that.

DeVorkin:

When was that?

Strong:

About 1950.

DeVorkin:

I'm interested though in the very first years, when you started supplying gratings to Tousey and to others.

Strong:

Oh. that's a story I want to tell you about.

DeVorkin:

You said Bowman himself put you in charge of the ruling engines?

Strong:

Bowman called me over to his office and told me to take charge of the ruling engines. I was in charge of the engines when Tousey got the first of the gratings he needed. Bowman charged me as follows, "Strong, industry is going to make gratings eventually. If they do better than you do, I'm not going to hold it against you. But don't you let any other university get ahead of Hopkins in gratings. If that happens I'll hold you responsible." Then Pfund saw me and said, "Strong, do something about gratings." And ONR said, "Here's money to do something about gratings." Well. what would you have done? You'd start working on gratings. ONR gave me very good advice. They said, You may wish to work on replicas. But they added, "That's not a command, that's a suggestion. You do what you please." I pleased not to work on replicas, and that was a mistake. I worked on improvement of the ruling engines. Wilbur Perry, alone, operated the engines. They are very unforgiving of mistakes. I did get involved once: my student, Harold Stewart, came to me with an idea to invoke physical optics for blazing. He proposed to rule 50 grooves at 5 spacings; then, one at 4 spacings. This was to be repeated until the face of the blank was covered with grooves. He predicted that all the orders would be absent for the spectrum lines except in one order. Our policy (Andersons advice) was "to jump first, then think." Perry stood aside so that Harold and I could spend all day putting a shim in the spacing mechanism — for one groove after every 50 lines were ruled — the spaceing pawl causing an advance of only 4 (rather than 5) teeth on the dividing head. You can imagine our excitement to test the result that evening. True enough, the spectrum line was absent in all grating orders but one. However in all the absent orders there was a mess of thes strongest Rowland Ghosts (of the missing line) that I ever saw. And so his idea went into history — a beautiful experiment that said "No!" When I got ONR funding for work on gratings, the first thing I did was to procure a very sensitive instrument and measure the precision in repetition of grating groove spacings. Stimulated by the results, I invented a new method of lapping a precision lead scow. Eventually, a new ruling engine was made applying my invention. The idea and the associated design worked out so well that the very first grating that Perry ruled with the new engine was free of Rowland ghosts — so that no cross rulings were ever made. I am getting ahead of myself in chronology since the new engine came to completion after the opportunity we had to rule gratings for Dr. Tousey's V-2 spectrograph.

DeVorkin:

Did you know Tousey before that time?

Strong:

Oh yes.

DeVorkin:

How did you meet him?

Strong:

At NRL. I knew all of Hulburt's group, Tousey and Sanderson especially. Dr. Tousey posed us a difficult problem. He needed a concave grating of short radius of curvatus, only 50 cm. And he wanted it blazed for the ultraviolet — centered at about 2000A. Perry said it couldn't be realized because that blazing meant a very shallow group. The heavy diamond loading required for such shallow grooves would not produce equal grooves — their depths would vary. I take credit for suggesting that he try it anyway, with a thin coating of aluminum. A thin coating, of itself. would require heavier diamond loading. We ruled gratings on six blanks supplied by Tousey. it turned out that Perry's fareboding was valid, but it did not take account of beginners luck. Of the six rulings Tousey found one that was fair. He rated the other five as poor gratings. It was with the fair one that Tousey "drew first blood" — the first spectra of the sun for wavelengths below 2900A. We made many futile attempts to do better. Dr. Friedman made electron-microscope pictures of the "fairly good" grating grooves, trying to uncover the reason why one of those original six was better than subsequent ones.

DeVorkin:

Wood had already developed blazed gratings?

Strong:

Oh yes. But that was on speculum metal grating blanks. We never considered speculum metal blanks for Tousey. Maybe that would have worked better.

DeVorkin:

You modified it for evaporated aluminum on glass?

Strong:

Exactly.

DeVorkin:

Herb Friedman did electron miscroscope pictures of Tousey's gratings. Do you have those pictures, by any chance, anywhere?

Strong:

I must have them somewhere but I don't know how to find them. I'll have a look for them.

DeVorkin:

It would be very interesting, if they were retrievable, to get some copies of them so we could record it for posterity. Now, I know that the Applied Physics Lab at this same time, in a group with James Van Allen, were designing spectrographs as well. Were you involved at all with them?

Strong:

No. I wasn't involved with Van Allen.

DeVorkin:

Why is that? Because he must have been quite close to you. Did you have contact with the APL group there at all?

Strong:

Not much. I knew Gibson, who was the director for many years, but I never had much contact with their projects.

DeVorkin:

I see. Can you speculate as to why?

Strong:

No. I think they felt we were kind of pampered children that weren't accustomed to tight deadlines, etc. etc.

DeVorkin:

Was that the feeling of APL generally or of Van Allen or what?

Strong:

I really don't know. If I knew and it was tactless to tell you, I'd tell you anyway!

DeVorkin:

I know that J.J. Hopfield and Harold Clearman worked with Van Allen and they did build some spectrographs. The gratings were the same design, it looked like, as the ones of Tousey's. Did they come from you or some place else?

Strong:

I don't remember that they came from me.

DeVorkin:

Had you developed any interest in the ultravoilet as a result of your contact with Tousey?

Strong:

No. The only interest I had in the ultraviolt was the Hartley Band of ozone — the band involved in the ozone-height work mentioned earlier.

DeVorkin:

Did you follow their work? Watanabe of course was with them by that time and they were doing ozone studies. Did you involve yourself at all with them or talk to them about it?

Strong:

No. My interest in ozone was long past then. With Martin Summerfield, I had measured the pressure effect of ozone absorption in the 9.6 mu band. Summerfield, who got his PhD at Cal Tech on that work, became prominent in jet engines, later becoming Professor of Jet Propulsion at Princeton University. He became my student at Cal Tech after he had done a research study of a vacuum-spark stripped atomic spectrum for his PhD under Professor Bowen. Just as he finished it, a paper by Edlane, a Swedish spectroscopist, came out on the same spectrums. Prof. Bowen asked me if I had a problem that would make a quick second research for Summerfield, and I offered the ozone problem. The way he got into jet propulsion is notable: At a party, after that work with me, Dr. Theodore von Karman asked him if he knew anthing about the infrared. He cited his work with me. Von Karman then asked him to look into heat transfer between hot gases and solids. He said it was known that the Germans were burning fuel in jet engines at a great rate — Prof. Gage (of Cal Tech chemical engineering) allowed it would require a fire box at least an order of magnitude larger than their engines. Summerfield soon had things in hand. He put a graphite plug in an experimental jet engine that reduced the jet from 3 inches diameter to 1/2 inch diameter; but, at the same time it doubled the jet's thrust. I don't know the details, but it was his kick-off in jet propulsion.

DeVorkin:

Let me ask , then, during the first few years back at Johns Hopkins, you were making gratings, you were working in the infrared, and you started to have students. Is that all correct in that order?

Strong:

Yes. I taught the Electricity and Magnetism course at first. Then, after Prof. Pfund retired I taught Optics. And I conducted a weekly Seminar on a wide variety of topics — generally by invited speakers. (Once we had a lecture on Easter Island by a National Geographic photographer whom I knew.) I had over 2 dozen PhD's at Hopkins — and not the worst at that. When Hopkins had its centenary celebration they had, on the program. a seminar (or something like one) with a dozen of their physics PhDs who had succeeded in the outside world. A large majority of that dozen were Strong's PhD students. That made me proud. My teaching of classes was without benefit of ever having had a course as a student in optics on spectroscopy. I don't recommend that — but, it does give a fresh point of view. I taught E and M from Harnwell's text — a truly wonderful book. I learned a lot. Prof. Ditchburn — who wrote a wonderful book in Optics — once said to me, "When you take a course in Optics you learn it. When you teach a course, you really learn it. But, when you write the book, you really do learn it." That was my experience except for the first phase. In E and M. I worked every problem in Harnwell's book during the first year I was at Hopkins. It certainly kept me out of mischief.

DeVorkin:

That's marvelous. Were your interests changing at all? Were you getting more and more interested in astronomical problems during this period?

Strong:

I was most involved in developing instrumentation for infrared spectroscopy.

DeVorkin:

Laboratory spectroscopy.

Strong:

By the mid 50's I was ready to claim telescope time with the California telescopes. I had designed and started to build an infrared monochromator at Cal Tech. It was completed in Baltimore. It was intended for the study of the planets. My student William Sinton, who is now an astronomer in Hawaii, collaborated in these studies. I must tell you of another physicist that I "seduced"! at Hopkins. The story is not a very cogent one to your purposes but I'll give it anyway. In 1949 (I believe it was) I was Chairman of the Physics Dept. for one year. When Prof. Pfund retired he must have recommended me to Dr. Bowman as his successor. Anyway Bowman called me to his office. When I was seated he said "Strong, look at the clock and tell me what time it is." I said "9:15". To this he responded, "You say "Yes." and at 10 o'clock you'll be chairman of Physics." I said that I would need first to consult with Bearden and Dieke, I couldn't say "yes" because I knew those two had each planned for the chair for many years. The first thing I then did was call on Pfund. He was at home, ill, having retired owing to his heart. The long and the short of it, was that Bowman established an arrangement by which Bearden was chairman for one year; Dieke for the second; and then Strong for the third.

After that the Physics department was to vote on their preference for permanent chairman. That all happened and Dieke was elected after my tenure. I pushed to get Schrodinger as a professor during my year. For some reason that was a mistake. To get back to the seduction story. During my year as chairman Prof. Gilbert Plass came to me and said he wanted a summer job. I had written a memorandum on the stratosphere and had drawn some intuitive inferences. I gave him a job with stipend from my ONR funding. Dr. Waterman at ONR had liked my stratosphere fantasies so much that he had had them printed up as an ONR publication. I assisgned to Plass the job of translating that intuitive fantasy into mathematical logic. I say I "seduced" him because, at the time he was probably still involved with the same subject as his Princeton dissertation. "action at a distance" — a very esoteric theoretical or more properly philosophical matter. He found my intuition was correct; and he then and there converted his physics interests to meteorology. He has since become prominent in that field. He is a Professor in Texas now. I think it was the reality of the stratosphere that got to him.

DeVorkin:

I'm curious about a number of questions concerning your work with Sinton. Why did you wait so long to publish the work on infrared radiometry of the planets? It finally came out in 1960. Was there any reason for that?

Strong:

I don't recall any special circumstance.

DeVorkin:

Well, unless we don't recognize it, the first article with William Sinton is. "Radiometric observations of Mars." ASTROPHYSICAL JOURNAL. I 31, March 1960.

Strong:

We may have waited too long; but there wasn't any special reason. The APJ took our paper promptly when it was submitted.

DeVorkin:

Did it take a long time to reduce the data?

Strong:

It just took Sinton a long time at Hopkins to finish his dissertation. Prof. Dieke was one of his dissertation referees. In his thesis, whenever he referred to Venus he used the adjective "Cytherean." When Dieke saw this, he said, "the Venus atmosphere is not Cytherean, it's venereal." Dieke's only criticism was the use of that one adjective.

DeVorkin:

Of course, to be correct. Let me ask you the opinion of other Mt. Wilson astronomers who were at that time in favor of planetary astronomy. Were people happy that you were doing planetary, or did they say that planetary wasn't important?

Strong:

Perhaps they tolerated me because they owed it to me. Nicholson was, as I intimated by my story, interested in the moon, and Petit was interested in the moon.

DeVorkin:

Why don't you think there was more support for planetary astronomy in the 1950s? Do you have any feeling about that?

Strong:

No, not really. All scientists are blind, you know. You get more and more interested in what you're interested in, and you don't pay much attention to anything else. I never worried about want of support.

DeVorkin:

So in a way they owed you telescope time.

Strong:

That's right. I didn't have any cronies in planetary work there at the time.

DeVorkin:

Did you have contact and correspondence with Gerald Kuiper during that period?

Strong:

I was at a meeting in Tuscon, the only time I remember contact with Kuiper. But it was a memorable occasion. At the meeting Lewis Kaplan said there was spectroscopic evidence for water vapor in the Mars atmosphere. Kuiper's reaction to this was, "I wouldn't believe that if you proved it."

DeVorkin:

When was that, in the sixties already?

Strong:

Late fifties.

DeVorkin:

This was before or after you were working on the balloon-borne studies of Venus?

Strong:

It was before, as I remember.

DeVorkin:

Were you interested in the possible atmospheric water vapor content of Mars as a problem?

Strong:

Yes. We had tried for a balloon flight on Mars. But it was unsuccessful — the balloon was a leaker.

DeVorkin:

I wanted to ask you a quick question about your general feeling about the science that was being done at places like NRL after the war. How would you characterize the science there, as opposed to science that was being done at university laboratories such as at Johns Hopkins, Cal Tech or Harvard? Were the scientists any different? Did they have different goals?

Strong:

I have lost contact with NRL and ONR for the last 10 years. I suppose the situations there may be less propitious now. I can only testify to my opinions of the 60's and before. When Dr. Hulburt invited me to give up my Hopkins professorship and to join NRL (as he did in about 1960), I didn't accept his proposal from want of respect for the work of his group, and of himself — I declined from inertia: I did not want to move to D.C. I think the work of his group was as good as any of the places you mention. Perhaps the personnel was better. The NRL situation was patently the result of Hulburt's leadership. The situation at ONRL was also a result (as I understand) of Charlie Lauritsen's influence on the Navy's Admirals after WWII. It was the model for AFCRL, which has been a kind of ONR-NRL combination. I'm inclined to suspect that Hulburt was also involved here. ONR-NRL had set a fast pace. Of course Tousey's work has the highest merit compared to any of the places that you alluded to, it ranks absolutely first class! The admirals in the Navy apparently took good advice on the organization of ONRL. I think that the Navy is a superior service for the simple reason that they've always had to rely heavily on engineering or they'd sink. The Army can tolerate a little more incompetence than the Navy can. I think it was Charlie Lauritsen who briefed the admirals on how to set up ONRL so that it worked for creative scientists.

DeVorkin:

I know there was a group of young scientists called Bird-dogs or something, just after the war?

Strong:

I don't know a thing about them. I have a consumer of the privileges — not a policy maker.

DeVorkin:

Okay. One thing we missed from this period also, approximately 1946-1951: I read somewhere that there was a period of time when the Army Air Force had B-29s that it wanted to provide to scientists to take instruments up into the high atmosphere to do cosmic ray work, etc., and part of that mentioned that you were to take infrared —

Strong:

Yes, I did.

DeVorkin:

Could you describe that work?

Strong:

It was the B-29 that had the tunnel in the middle of the fusilage.

DeVorkin:

That's right.

Strong:

We only flew one mission with the it.

DeVorkin:

What did you do? What kind of instrument did you prepare?

Strong:

We measured the spectrum of the sun from high altitude with our KBr-prism infrared monochromator.

DeVorkin:

You have a publication on the infrared spectrum of the sun. let me find the actual reference —

Strong:

With Stoeffer?

DeVorkin:

"Solar spectrum from 3.3 to 4.2 microns" with William Benesh and W.S. Benedict. Did that come from this work?

Strong:

No. King McCubbin flew that B-29 mission. I don't think it resulted in a publication.

DeVorkin:

Was there another one that you did?

Strong:

Yes. There was another one. It turned out that the Air Force wanted an infrared spectrum of the sun from even higher altitude. I had some connections, and Kelly Johnson who was in charge of the U-2 aeroplanes at Northrup, agreed to let me put instrumentation in one of them. Frank Isaacson of ONR provided the funding. We only had one flight. When we published the results (I think Stauffer and Palmer were the authors) they prevented us from disclosing the altitude. I suppose the Air Force knew the altitude — we didn't. This was because the U-2 was a sensitive subject — especially, before Powers got shot down over Russia.

DeVorkin:

What was the Air Force interest in the far infrared spectrum of the sun?

Strong:

I can only give you presumptions. I presume that the Air Force was more interested in the atmospheric transmission above 70,000 ft. (in the 8-14 mu window, etc.) than in the spectrum of the sun. It's easy to guess why from the context of these days' "Star Wars".

DeVorkin:

That's right. Were you ever asked to design an infrared experiment for an Aerobee rocket or any kind of rocket flight?

Strong:

No.

DeVorkin:

Did you ever have any interest in doing that yourself in the fifties?

Strong:

No. We got interested in balloons as carriers. We considered that the altitudes they reached were adequate for our purposes.

DeVorkin:

Could we talk about, first, the origins of the Johns Hopkins University Lab for Astrophysics and Physical Meteorology, and then how you got interested in balloons?

Strong:

Yes. Before that, I'd like to tell you about a paper that is pertinent to the atmosphere's transmission — a paper signed by Tait Elder and John Strong.

DeVorkin:

What year was that?

Strong:

Oh, about 1954. I can't remember. It was on the transmission of atmospheric windows.

DeVorkin:

Here it is, Tait Elder, "The InfraRed Transmission of Atmospheric Windows." Journal of the Franklin Institute, 1953.

Strong:

A Dr. Green from the Atomic Energy Commission asked me to make a review of the literature on infrared atmospheric transmission. That's what gives me the presumed idea about the Air Force's interest. I knew Tait Elder needed a job. He was a graduate student and he wasn't getting quite enough money to go on. I asked him if he would be interested in doing the leg work on Green's proposed program. I didn't intend to do it myself. Having been polarized by John Anderson's advice Elder took it on eagerly. The standard way to plot the atmospheric transmission, when it follows an exponential law, is to plot the logarithms of the transmission as a function of the optical path. I suggested that Elder start by plotting the window transmission we had observed between Fort Heath and Nahant — the Harvard data. And also, that he include Fowles' data. He came back with the thing reversed — he had plotted the transmission versus the logarithm of the optical path. But his plots gave straight lines. Straight line plots are very helpful for extrapolations. I decided that Elder had done something important, and I derived a formula for band absorption that gave straight lines, such as he found. I did this in response to his success so that I could join up with him on the project. That paper gave us a lot of satisfaction even though my claim to co-authorship was not very equitable.

DeVorkin:

So there was an extraordinary amount of interest by the military groups, both Navy and Air Force, in infrared windows and in the transmission characteristics of the atmosphere.

Strong:

Yes.

DeVorkin:

Did you regard this as personal field research or pretty much applied research to national goals, that sort of thing?

Strong:

I don't think it would be completely honest for me to wave the flag. It was just that there I was, in a situation, and this was a good way to cope with it. The situation was to do research along the lines on which I'd been going where I had some momentum; and, to provide programs that would be suitable for my students. That was my main motivation.

DeVorkin:

Did you have any sources of funding in the early 1950s other than ONR? Did Johns Hopkins fund you?

Strong:

Johns Hopkins didn't have any money for my work.

DeVorkin:

What about NSF? Did you ever apply for NSF funds?

Strong:

I applied once. I was told that the support which I had asked for was half of their astronomy budget. Although they turned me down, Dr. Harold Glaser, then there, was as helpful to me as possible.

DeVorkin:

What was that for?

Strong:

Balloon astronomy. Yes. Harold Glaser told me that I got a high grade from NSF's outside judges. Glaser tried to organize a group of sponsors to support me.

DeVorkin:

When was that?

Strong:

In 1966 — somewhere in there. It was just before I came up here. As a matter of fact, I asked the vice president of Johns Hopkins to come to the meeting of possible sponsors that Harold Glaser had organized. He said he'd come but he didn't. When he didn't come, I started looking for another job.

DeVorkin:

The same thing that happened with Max Mason when he didn't show up for the meeting.

Strong:

Yes.

DeVorkin:

And what was your motive behind that? I'd like to know when you did it and who you brought in.

Strong:

I'll try to give you the whole story, chronologically. It started from a request that President Bowman made of me. He wanted me to analyze, "confidentially", the use of space by the Physics Department in Rowland Hall. That was easy as I had inherited a set of floor blueprints from Professor Hubbard, when he retired. The situation blew up when Professor Bearden stormed into my office and asked what it was all about. He was angry. Dr. Bowman had further asked me what I would do with 1200 square feet of floor space in a new building that was contemplated. I told Professor Bearden that I couldn't discuss it. After he left I called Dr. Bowman and asked for an immediate appointment — and got it. The first thing I said was that I couldn't work with him "confidentially" if he leaked the matter. He reared back in his chair and let go a hearty laugh. Just then Bearden called him on the phone and I heard one side of the conversation. All I remember now is that Professor Bearden had a lot of influence. The matter did blow over, but it sowed a seed in my mind. The seed, I suppose, sprouted in the form of my wishes for a separate laboratory, later.

That sprouted when Dr. Detlev Bronk had become the President. Dr. Bronk didn't respond to my wish, and so I had to tell him I had two offers of research professorships. Taylor, a trustee of Stevens Insitute in Hoboken, was the catalyst for one. At the time when Stevens was having a renaissance. The University of Colorado at Boulder, was the other university. President Quig Newton tempted me to come to Boulder by mentioning that the Faculty Club Annex, in the mountains, had an associated private trout stream. Applying my education from the above-mentioned, Max Mason incident, I got my wish from Dr. Bronk. I got 1200 square feet of space in the New Ames Hall. Dr. Bronk even gave me an exaggerated title: Professor of Astrophysics and Meteorology. I ducked that one and asked it to be, rather, Professor of Experimental Physics — and so it appeared in the next year's catalog. I got one of my friends who was at the time (or had been). a trustee of Johns Hopkins University, Dr. Walter Baird to give Dr. Bronk a little push in my favor. That did it. Dr. William Benedict had been associated with us since the Senator McCarthy era — of which he was a victim. There were no other senior scientists — not counting three post-docs who came and worked in the laboratory — each for a year. One from Israel; one from Switzerland; the third from Japan. One of my proud accomplishments, in those days, came from my being a Director of Eppley Foundation. I found out that the Foundation was embarassed by too much money. Forthwith, I influenced them to establish a scholarship for students who had been forced to drop their graduate work (toward the PhD) by lack of funds. The scholarship was to have a larger than usual stipend. I argued that it would be at no risk since it would be given to people who were currently successful without a doctorate.

The first recipient was a black man, recommended by Dr. Benedict. He had been a hero in the Korean War — but his current family obligations prevented further PhD work. Mr. Judd's stipend was $6,000 a year. I had to leave him on Hopkins hands when I left in 1967. I don't know if he ever got his PhD. Parenthetically, I did something the Epply people disapproved of, so I resigned, and Judd's was the only such scholarship they supported. Diane Primz, my only, female PhD at Hopkins, got into the Shuttle program. I haven't heard from or of her recently and so I don't know whether she is making it in space, or not. She was at NRL for a long time. I believe she worked with Tousey some. LAPM was established in approximately 1952.

DeVorkin:

That's very interesting. And then you were director of the Laboratory of Astrophysics and Physical Meteorology from 1952 to 1967.

Strong:

Yes. Since my status was that of a department head, it gave me control over all the laboratory's property — property that I had accumulated under ONR, and other grants and contracts — I gave it to myself and brought it along when I came up here to Amherst. When I resigned, I conveyed whatever claim I had to it here, by formal letter, to my successor Professor Hjami Sakai. He was at Hanscome Field, Air Force Laboratory, when I propositioned him to take my place here.

DeVorkin:

Was there something of a problem, bringing all this property up here?

Strong:

No. Hopkins didn't have any objection.

DeVorkin:

But why did it make Time Magazine?

Strong:

Because there was a lot of it — appraised at about a million dollars. It included machine tools for a very complete machine shop; telescopes that I had built, etc.

DeVorkin:

Johns Hopkins didn't worry about it at all?

Strong:

Not to my knowledge.

DeVorkin:

Did you bring any astrophysicists in?

Strong:

I didn't have any to bring. I did bring Bill Plummer along. And I brought along William Mankin to do research work at University of Massachusetts for his doctorate — a doctorate that was later granted by Hopkins. Plummer was a brilliant experimentalist. He later moved on to Polaroid Corp. where he has been very successful. He was one of my PhD's who spoke at my retirment symposium — his speech is in the January 84 Applied Optics — along with all the others (save Martin Summerfield who didn't write up the reminiscences that he recounted here).

DeVorkin:

Tell me about the events that drew you into balloon astronomy. How did that happen?

Strong:

Well, I just responded to ONRL. They provided the initiative. They were interested in exploiting balloons after Winzen and Raven made plastic balloons available. ONR told me that they were interested in experiments — that exploited the new balloon vehicles and I responded.

DeVorkin:

In your SCIENTIFIC AMERICAN article on balloon infrared astronomy. you said that Shirleigh Silverman, Frank B. Isaacson. and Malcolm Ross approached you.

Strong:

Yes, that's right.

DeVorkin:

They represented ONR?

Strong:

Yes. Malcolm Ross was actually a Navy officer.

DeVorkin:

They inquired if you had any astronomical projects to be done from a Navy, two-man balloon. Shirleigh Silverman is somebody who worked with you before that.

Strong:

He never worked with me. Shirleigh Silverman got his doctor's degree at Johns Hopkins. He was a very good friend of mine and often visited Prof. Pfund and me there.

DeVorkin:

What I'm trying to understand is the following. The Navy had these manned balloons called Man High or whatever project it was, and these were clearly to be manned; that was a very complex operation. They were looking to you for some scientific experiment. Had they asked other people as well, or they asked you personally?

Strong:

I don't know whether they asked other people. I know they asked me. And I produced a project which they liked. At a meeting of concerned people the question came up, with respect to my proposal, of who would fly with Malcolm Ross. Ross said that he intended to invite me. Then they looked at me and asked my reaction. I said I would go. It promised adventure. When the time came, I was all suited up and locked into the balloon capsule with Mal Ross; the balloon was inflated and ready for take off, but just then it ripped open from top to bottom. People get a certain fever in such situations and Ross and I were both keen to turn at once to the second, spare balloon. But someone with authority said we must wait until the balloon fault had been resolved. By the time everything was "go-go" again, a year had passed. Charlie Moore, my second, took my place and made the first flight. We thought the meager data he got showed water vapor in the atmosphere of Venus (that was our project goal) — but the indication was not a hard one.

DeVorkin:

What I'd like to know is how you decided upon doing infrared planetary work with this, and how you set about designing the instrument that would go on the gondola?

Strong:

A Schmidt telescope with a 16-inch diameter mirror had an auxiliary small telescope of 3-inches diameter for fine tracking. It was practical to track Venus to within a degree or so with the large telescope in the gondola. And, because the small telescope had a moment of inertia orders of magnitude smaller it was possible by servo-control to track Venus with it to within an arc-second or so. How the optical features of the Schmidt telescope were thus exploited is described in my Ives Medal paper in J.O.S.A. My system has been used in large microwave telescopes that pointed to the zenith in order to track stars across a limited field — like the telescopes at San Juan, and here at University of Massachusetts. Being a relay system that picked up the image, the imaging in the spherical field of a Schmidt mirror transfered it to the spectrograph slit.

DeVorkin:

Did you use the Librascope startracker from the very beginning?

Strong:

Yes.

DeVorkin:

Will you tell me how that was developed and designed?

Strong:

Well, that was Morris Birnbaum's development. A rotating semi-circular, opaque disk, rotating about its center in the focal plane of the auxiliary telescope, chopped the planet image formed by its objective lens. When the planet was off center a signal from a photocell behind the rotary dish "knew" from its phase, in which direction the planet was off. This signal fed the servo mechanism that kept the auxiliary telescope and an optical relay system pointed at Venus.

DeVorkin:

What kind of detectors did you use?

Strong:

We used an S-1 photomultiplier tube for the spectrometer. It was responsive in the phi band. I think Langley was probably responsible for naming that. The S-1 photomultiplier tube is very sensitive there, so we used it.

DeVorkin:

Now, you had your first flight, that was in 1958?

Strong:

We thought we detected water vapor, but it wasn't hard evidence.

DeVorkin:

This was Venus. Your first intention was to do Mars, wasn't it?

Strong:

No. Venus.

DeVorkin:

Why so?

Strong:

To track Venus with the startracker it must first be acquired. and there is a lot of sky for the planet to be found in. However, the sun is easy to find and Venus was to be found on a circle of radius Beta (of about 450 radius) around it. Thus the sun served for the acquisition and rough tracking. The Beta was pre set and a sub system was programmed to roll slowly until the telescope found Venus. Then it went into another programmed mode to keep the telescope pointed at Venus within the field of the startracker (about a degree in diameter). One time in a telescope we saw this acquisition occur when the balloon was at least 25 miles away. So you see Venus was far easier to do than Mars. Morris Birnbaum used the same trick on Voyager. However rather than using the Sun as a fiducial point he used the bright star Canopus. That's why we went for Venus first.

DeVorkin:

Now, I'm confused. Wasn't your first one manned?

Strong:

The first one was manned. The reason we chose Venus for it was we thought Venus had the most chance of having water vapor and life. I was describing acquisition for our second unmanned flight. The better data it yielded was reduced by William Plummer, who was then a graduate student. He got positive evidence of water vapor — but it has never been confirmed. It is a mystery why his data indicated water vapor in the Venus atmosphere.

DeVorkin:

Is there a chance that you were looking at Earth's atmosphere?

Strong:

No. I don't think so.

DeVorkin:

You were up around 86,000 feet?

Strong:

Yes.

DeVorkin:

Now, you flew both manned and unmanned experiments. At that time, as you pointed out, there was an acquisition problem in an unmanned.

Strong:

Yes.

DeVorkin:

But what is your feeling now about the difference between manned and unmanned flights? Did you prefer one over the other at that time?

Strong:

At first, we preferred manned flight because we didn't have the technology for an unmanned flight. As soon as we got the techology, we preferred unmanned (then you don't have anybody in the gondola kicking).

DeVorkin:

That's right. Did you find that to be a problem, with the manned flights?

Strong:

No. Charlie Moore who finally flew in the manned flight from Rapid City says he didn't have any problem, either acquiring Venus or tracking it. Another factor in our case was funding. As you pointed out, the motivation of our first flight with the Navy was simply to provide a program that served their vector for manned flight. We didn't have either funding or the technology for unmanned flight at first.

DeVorkin:

When you went to unmanned, did Librascopes still do the star tracking or did you have a different source?

Strong:

Librascopes attempted it, but they never did produce a satisfactory system. We did that ourselves with Morris Birnbaum's collaboration as a consultant. Librascope Co. had Birnbaum in Binghamton, NY and we established a laboratory in a Howard Johnson's motel there in order to use him. We got funding for the unmanned flight from the Air Force. It owed to the efforts of Knox Millsaps. When we got funding we gave the contract to Librascope to make our design because we had had such satisfaction with them before. I wanted to write Morris Birnbaum in the contract, but they objected to "black and white" as a matter of policy. Rather, they gave us verbal assurance that he would be our project engineer. Actually, they never assigned him to us. Rather, they assigned a green engineer who first off bought and used germanium rather than silicon transistors. This was a mistake that cost us dearly: They were cold sensitive and we had to correct this mistake by making a capsule to go in the gondola to contain the germanium electronics. Even so, the system they tried to deliver to us would not work. We finally had to take delivery of it. I then sent a Hopkins group to Binghamton (where Birnbaum was working on a Librascope job). Birnbaum was granted permission to consult with my group in the evenings. When the system finally functioned, and my group came home, I had to buy a new rug for the HowardJohnson motel room that my group had used as electronics shop — the new rug became the old one which was infested with dropped molten solder, which couldn't be cleaned up. On our first flight with that system — flying out of the Holloman Balloon Base — the startracker failed. The minute the flight was off the ground Birnbaum told me it wouldn't work. The vacuum tight electronics capsule hadn't been sealed. There's a lot of excitement just before launch; with three or four people walking all over each other each to get his particular part of the gear ready. It's a wonder it ever works. We had check lists, of course, and a system. but our system failed once. On the next flight the star tracker operation was unsullied.

DeVorkin:

Good. Morris Birnbaum, the electrical engineer who was responsible for this startracker success is now at JPL, just so we know. Let me ask you a few other questions about the early ballooning program. Your funding started with ONR, of course, but then it shifted to Air Force in 1961. Why was that? Was that when you switched to unmanned flight?

Strong:

I had been at Cloudcroft, N.M. several summers to participate in study groups that were organized by Dr. Knox Millsaps. (Knox is now a professor living in Gainesville, Florida). He was then in charge of the Air Force science at Holloman Base, Alamogordo. Before or during the time after he got funding for us, he was Chief Scientist for the Air Force. That, I hope, identifies our patron. Well, on one of those summer visits Knox asked me to write up a paper describing what could be done with balloons. I entitled that paper, "Observations with Satellite Substitute Vehicles." After that, he asked me how much money it would take to do it . This was after our experience at Rapid City, I estimated at half a million dollars. He said "Sold." His general went up to Air Force Cambridge and arranged to get me that money.

DeVorkin:

So you switched to Air Force money in '61. What were you doing at Cloudcroft before that? I am curious because that was an important groundbased planetary observatory.

Strong:

The Millsaps studies, were independent of the Air Force's solar observatory on Sacramento Peak. Incidentally, I have one of my PhD's there at Sac Peak now — Dr. Raymond Smartt. He is an example of how academics can waste talent. They failed him on his doctoral exam at the University of Rochester. Then he turned to me here in Amherst. While here he invented the Point Diffraction Interferometer — a very useful interferometer that could have been invented a hundred years ago. It was there before all eyes until Smartt saw it. Of the study topics that Millsaps organized: One was concerned with the design of an enormous solar furnace. It was never built. It was to be at a site in the area named "Hot Spot" (in comparison to "Sun Spot"). Another was a series of lectures that included a lecture by Dr. Robert Oppenheimer. Another summer (this time in Gainesville) Millsaps had a group together to study the potentials and promise of positive ions for jet propulsion.

DeVorkin:

I still want to talk a little about the balloon work and your general impressions of the way to do it at the time. You mentioned that the technology was really not there in the beginning for unmanned acquisition. I take it the acquisition of a planetary image is quite a bit more difficult than a solar image.

Strong:

The sun is 23 magnitudes brighter than the planet, and so we arranged a suntracker with a biased rotation so that when it found the sun, the telescope would be pointing to the circle around the sun on which the planet Venus was to be found.

DeVorkin:

Okay. Is there anything else we should cover about your early balloon work itself that would help us understand the technology that was used?

Strong:

It should be pointed out that I had had many flights before the "Man High" thing. They were supported by the Air Force. Smaller balloons were involved. The scientific objective of those flights was to determine the infrared-flux gradient in the atmosphere as a function of height. The scientific instrument used was a scanning infrared (grating) spectrometer. It looked alternately up and down (up as steep as possible and yet avoiding to see the balloon above, and down at the same angle to the nadir). I think the work with balloons after that has been pretty well covered.

DeVorkin:

When you had major disasters, like when the balloon ruptured and that sort of thing, did it ever cause you to think twice about whether this was the right way to do science, or maybe it was too risky?

Strong:

Yes — I though about it many times. Winzen and that outfit was substantially more cavalier than we were. In fact, we didn't make very many mistakes or suffer due to our own negligence. I was inclined to over-test. Not as much as NASA does, but certainly far more than a cavalier outfit like Winzen.

DeVorkin:

What contact did you have with other early astronomical balloonists like Schwarzschild or A. Dollfus?

Strong:

Dollfus visited us and, Schwarzschild visited us and I visited him at Princeton. I'm very fond of Schwarzschild, he's a beautiful person. He told me once about the Cambrian Tribolites (these fossils were the hobby of Franco Rasetti. He was one of the co-inventors of the "pile" that yielded the "bomb" — with Pornicovo and Fermi). Swarzschild said in those early days of the Tribolites, when they "looked" at the heavens, if they ever did, they couldn't have seen the Pliades for those sisters had not yet been born.

DeVorkin:

Of course, stratoscope I was only for the sun, but Stratoscope II, the 26-inch, looked at the nucleus of Andromeda and things like that and of course was unmanned. Was it using a fundamentally different design for the star tracker?

Strong:

Yes, I think so. If I remember correctly one of the astronmical objectives in my NSF proposal for infrared study — mentioned earlier — was the infrared radiation from the center of our universe: an objective is set forth in the NSF Proposal that Harold Glaser tried to help us with. That objective never came from Schwartzchild, nor passed to him. I just figured that the center had to be at least infrared hot, if not hotter — overed up by dust which the infrared might penetrate. I may be fantasizing about it now. I have no copy of that proposal to check.

DeVorkin:

Were you working at the same time? Were you still working with Librascope at that time?

Strong:

No. I think Stratoscope II came after us.

DeVorkin:

Every so often in your writing, I see that you had been planning a larger telescope such as a 50-inch. How far did any of those projects get?

Strong:

They didn't get past the gleam in our eyes.

DeVorkin:

Why was that?

Strong:

Well, you always play a talk game and a hard ball game, you know, and that was our talk game.

DeVorkin:

Were you in competition with Schwarzchild or anybody like that?

Strong:

I never felt so. As you well know, there was money for everybody at that time.

DeVorkin:

In the early sixties?

Strong:

Yes.

DeVorkin:

Let me ask you: you already mentioned your U-2 flight which was about 1960. What kind of contact did you have with the early NASA airborne program as they began to use Lear Jets and U-2s? They were doing infrared work after all.

Strong:

I had no contact.

DeVorkin:

That was Frank Low and Neugebauer and others. But you had no contact with them?

Strong:

Well, Frank Low developed very good detectors. When I came up here in 1967 I had contracts, but they hadn't finished my building yet. I used some of my funding then to buy a Frank Low detector.

DeVorkin:

But you had no contact with him earlier or when he was designing instruments.

Strong:

No professional contact. I did see him occasionally at scientific meetings.

DeVorkin:

I'm just trying to determine if you had given him advice or consultancy —

Strong:

No. They largely played their game their way and I played my game my way.

DeVorkin:

Okay. Infrared astronomy of course was growing in the sixties, and there was more interest in planetary infrared work as well as stellar and galactic. Were you anxious to get involved in that in a greater amount?

Strong:

I do not remember any consort with Tousey or with Newkirk on coronagraphs. I invented a novel coronagraph — novel to the extent that it used a paddle instead of an occulting disk. The diffraction of the paddle edge is much less than from the disk edge, although it is occulted in both cases. You see, we weren't interested in all of the corona. We wanted to scan only on one diameter. I used a paddle because it gave me immunity to nodding of my gear, which was tightly servo'd in azimuth. I had a student who was very careless, in his publication, about the origin of the paddle idea.

DeVorkin:

Between June and December of 1960 there was a series of conferences sponsored by the Space Science Board on planetary atmospheres. Al Hibbs and Ray Newburn and L.D. Jaffee and others from NASA and JPL were involved, and everyone was talking about how to do planetary atmosphere research. Were you at those meetings and did you play a part?

Strong:

I don't think so. If I was, I don't remember. Incidentally, when I got my Millsaps funding for balloon astronomy, I sponsored a conference at Johns Hopkins. My student, Wm. Plummer, wrote up proceedings for it. We had the conferees discuss what they'd like to do, and what could be done with balloons.

DeVorkin:

I'm quite sure that although you may not have been at the actual conference it looks like you wrote one of the appendices, called "Observations from the Satellite Substitute Vehicles."

Strong:

Oh, that's the paper I wrote for Millsaps, mentioned earlier.

DeVorkin:

This was part of the Planetary Conference, with special reference to Mars and Venus, held by the Space Science Board of the National Academy of Sciences in Arcadia, California. You didn't go to that one?

Strong:

I don't remember going.

DeVorkin:

It was reprinted in this PROCEEDINGS. Lloyd Berkner, Hugh Odeshaw, of the Space Science Board provided the foreword to it, and it's called "The Atmospheres of Mars and Venus, a Report by the Ad Hoc Panel on Planetary Atmospheres of the Space Science Board." prepared by Kellogg and Sagan, publication 944, National Academy of Sciences, 1961.

Strong:

At the Hopkins meeting that Plummer reported, Bruce Murray pointed out the necessity to avoid seeing the infared emission of the telescope itself. Bill Sinton and I had crossed that bridge several years earlier when we found that the observed spectrum of Venus, with the 200-inch telescope, was quite different when the Venus radiations were chopped with reference to adjacent sky (sky that was reflected so it substituted Venus, accomplished by means of a two-aluminized-mirror chopper), and when the sky was chopped with respect to Venus, with the two paths interchanged. This is described in our 1960 Astrophysical Journal paper. The difference was laid to the infrared emission of the chopper. About then Bruce Murray, or others, proposed to solve that problem by cooling the telescope to liquid helium temperatures. I wrote a report on a method of doing it with tesselated tubes. It was an awkwardly proposed solution to an awkward problem.

DeVorkin:

DIRBE was the IRAS that was flown last year.

Strong:

Was it? Has it been flown?

DeVorkin:

Yes.

Strong:

Five or six years ago it was called DIRBE or something like that — Diffused InfraRed Background Evaluation.

DeVorkin:

I see. Maybe this is a different one.

Strong:

I don't know. DIRBE was to have a telescope in a liquid helium cryostat. I got involved with DIRBE much later, and quite unofficially, when I was a visiting professor at Tuscon (over 5 years ago). The Optical Sciences Center showed me a description of the DIRBE project then. I thought it was almost as awkward as my awkward cryostat. I proposed, rather, the use of a novel interferometer and Fourier Spectroscope, a "natural" for DIRBE. I figured out an alternative system and submitted it to NASA, free lance. They ignored it on the basis of a policy to fly only flight tested components — certainly a poor policy — every component is on its first flight once. My novel interferometer was criticized by my former students, Sakai and Vanesse, as yielding awkward interferograms because the interferograms were displaced from zero path difference. I worked on that for months and I have proved conclusively that with a small trick, the interferogram is only different from interferograms that started at pathdifference zero — it is only necessary to involve a sine and cosine transform, rather than a simple cosine transform. That's a small price to pay for all the many advantages of my system. I would lay a bet that some day it will be done again, my way. My DIRBE proposal didn't involve any prisms or conventional gratings. The only window in the radiation path was the window over the detector, and even that you wouldn't need in space. So it was an almost all mirror system. Work in the far infrared presents materials problems: what's transparent, what can be used as filters, how to separate the spectrum into different parts, etc. By use of Fourrier transform spectroscopy all optical filtering is done electronically.

DeVorkin:

Do you feel that you played any part in setting scientific policy, or how science should be done, in the early planetary conferences?

Strong:

No. I did have some involvement as I was a member of the Scientific Advisory Board for the Air Force for five years. Joe Kaplan was the chairman of our panel on meteorology; Fred Whipple of Harvard was always proposing to get something up there in space before the Russians do it. The reason Whipple was so wise about this was because he knew that the Russians were publishing papers on comets and meteorites, and he guessed that there was more behind the activity than scientific interest.

DeVorkin:

There is no date on your vita for when you were on that board. It was during that period that Whipple was advocating space?

Strong:

Yes. It was 1950 to 55, before Sputnik.

DeVorkin:

Let me ask you one or two more qustions about the balloon work and then we'll move on to a few final things. First of all, what is your feeling about the role that science played in doing these scientific experiments on the manned balloon flight? Was the science kind of bootlegged on, or was it really a good program for science?

Strong:

Oh, I think it was a good program even though it was a bit bootlegged and a little bit wild at times. There's a lot of wild science — in which the people trust that luck will be with you. My policy has always been to trust that luck will be against you.

DeVorkin:

Is that your philosophy?

Strong:

Yes.

DeVorkin:

So you try to account for everything.

Strong:

For everything.

DeVorkin:

In your study of the Satellite Substitute Vehicles, that you mentioned you'd done, and that I found the reprint of, you talk about the role of border of space — nice term, border of space observatories — and indicated that one of the uses of these were proof tests of instruments for satellite experiments.

Strong:

Yes.

DeVorkin:

Could you tell me, in your mind, what your priorities were at the time when you built these manned and unmanned balloon observatories? Was it more important as a proof test for space satellite observatories, or were you primarily interested in the data gathering?

Strong:

I was primarily interested in the data.

DeVorkin:

You don't see yourself as a stepping stone?

Strong:

No.

DeVorkin:

Okay. I know that even though you didn't do any direct work on satellites, designing optical systems and that sort of thing, you did give a paper at a NASA workshop in 1970 on space optics for a Large Space Telescope. I'm just wondering how close you were to the development of the design for Space Telescope?

Strong:

I wasn't involved in that.

DeVorkin:

Early on, as the Space Telescope was being designed, I know that they had planned to put infrared instruments on it as well as visual and ultraviolet. But as you say, you weren't directly involved?

Strong:

No.

DeVorkin:

There's one large area of work for which you're known that we haven't talked about in any detail, and on which I thought we could spend some time. I would like to have your recollections of how you got involved in interferometric spectroscopy. I know you did a lot of that in the 1950s.

Strong:

I was in Europe in 1949, and I visited Peter Fellgate who one might say was the father of Fourrier transform spectroscopy. However. Wood and Rubens did it primatively in Berlin in 1910. As a matter of fact, I came very close to getting involved in it at Cal Tech. but I didn't. When I visited Peter Fellgate he showed me spectra of a Globar, and of a Mercury arc that he recovered by Fourier transform of interferograms of the radiation they emitted. I was impressed but not converted. The computations involved didn't appeal to me: If you take a thousand read-outs from an interferogram and want a thousand spectrum points to plot, then a million calculations are required. That's not catnip for an experimentalist. The far infrared emission from a thermal source is relatively very weak — being proportional to the absolute temperature whereas the near infrared is proportional to temperature raised to the fourth or fifth power. Accordingly, one needs to use several selective devices (rough mirrors, black paper as a filter, crystal quartz filters and a Rubens shuttle) to avoid being "drowned out" by the Strong scattered near infrared. It suddenly struck me six months later when I was in the Chicago airport that if an interferometer in series with a far-infrared spectrometer were scanned so that the path difference was a linear function of time, it was promising that such an interferometer would modulate the long wavelengths at a low frequency while the shortwavelength, scattered radiation, would be modulated at a high frequency. In short, the detector response could be electronically filtered to yield the equivalent of optical filtering. I called the proposed device an "interferometric modulator". When I got back to Baltimore my students, Sinton and McCubbin, used the idea, and it worked. Also Bob Madden proved it out for the visible spectrum. I got involved in doing interferometric spectroscopy at Hopkins owing to the iniative of George Vanasse. He asked to use the interferometer modulator after it had served its purpose and was idle. He had become converted to Fellgete's idea; and that became the subject for his doctoral dissertation. He determined the far-infrared spectrum of atmospheric transmission — around 100 mu.

DeVorkin:

Was that in the fifties?

Strong:

In the fifties.

DeVorkin:

You continued on looking at different types of interference spectroscopy and transform spectroscopy and I noticed in the seventies you wrote a few papers on Hadamard Transform spectroscopy.

Strong:

That involvement too owed to Dr. George Vanasse then and now located at the AF laboratory at Hanscomb Field. He inspired us this time with a proposal of AF funding. The Hadamard scheme is a clever one and I believe we were the first to reduce it to practice effectively.

DeVorkin:

Did you have any contact with others who were doing Hadamard like Martin Harwit over at Cornell?

Strong:

No. We did it out of whole cloth. Although we probably got some feedback from Harwit through Vanasse, we were pioneers in that field only in a secondary sense of induced pioneering.

DeVorkin:

Okay. I'd like to have your recollections of R.W. Wood: what kind of a person was he? What are some of your personal anecdotes you have of him?

Strong:

Oh my, you'll be here till evening, or all night as well. As I've said before, I don't know what there is about me but I've always had an easy relation with people that were very competent like Hale, Millikan, Wood, Pfund and Randall. My first real contact with Wood was when we worked together, as I've told you, on the grating-spectrum anomolies. That was when held heard my paper at Berkeley and came down to Pasadena to work with me for a couple of weeks.

DeVorkin:

When you split the grating?

Strong:

Yes.

DeVorkin:

That was his character, to really exhaustively examine problems like that.

Strong:

Actually, the first example of the Echelle grating, which is important in atomic spectroscopy, was done by Wood.

DeVorkin:

Didn't Harrison —?

Strong:

Well, Wood was before Harrison. The echelle was inspired not by Wood or Harrison, but by an astronomer by the name of C.D. Shane of Lick Observatory. When he found out I was in charge of gratings at Hopkins he wrote a letter to me suggesting crossing a coarse grating with a fine grating in order to "write" the spectrum line by line on a photographic plate that was no bigger than a postage stamp, so to speak, instead of just one long straight line. He gave the idea to me because he knew R.W. Wood was careless about credits. I got Wood interested in it, and if you read Wood's paper. you'll find out he gave Shane full credit for the idea. Wood took two gratings — coarse blazed gratings — which I had ruled for him, and crossed their dispersions. He did this at his summer home in Easthampton, Long Island. He photographed a spectrum of a white-light source on a Kodachrome plate.

DeVorkin:

On Kodachrome?

Strong:

On a Kodachrome plate to give a colored spectrum from the blue to the red. And when he showed this at the Optical Society, everybody rose up and gave him a standing ovation! It was dramatic. Wood was of course a showman.

DeVorkin:

Was that the late forties when he did that?

Strong:

Yes, I think so. The abstracts of OSA meetings would tell.

DeVorkin:

I'm wondering because Harrison is usually credited with the design. Why is that? I should, perhaps, put it this way: Shane conceived the concept: Wood demonstrated it first; and then Harrison, in collaboration with Bausch and Lomb, developed the procedures to rule the coarse spacings of the echelle properly. I am giving you my impressions. The gratings Wood used were actually two identical coarse gratings. I had developed a way to evaporate thick coats of silver with very Strong adhesion. The grating was ruled on one of my thick silver deposits. Wood may have cut one large ruling to give two coarse gratings. He used the shallow groove-facet faces for the lowdispersion spectrum, crossed with the high-disperson spectrum yielded by the steel groove-facets faces with the other half.

DeVorkin:

It sounds very balanced, very fair. As you look back on your career — and you've done many many different things — what do you look back upon that has given you the most satisfaction?

Strong:

Crystal growing.

DeVorkin:

The crystal growing? Tell me why?

Strong:

Well, it's the first thing I ever did that everybody (but Stockbarger) appreciated.

DeVorkin:

Was there something in the way you did it or the completeness or the success that makes it the most memorable?

Strong:

Max Mason gave me a nice compliment once, when I was having this conversation with him about resigning. He said, "The thing we like about you, John, is you finish." And I think the thing that I did on the crystal growing was finish. In fact, all I did was to find the paper in the German journals by Stöeber which defined the conditions for growing crystals from the melt. and I applied them and finished the job.

DeVorkin:

And that was a very clean cut thing. You wrote another major textbook.

Strong:

Concepts of Classical Optics.

DeVorkin:

It doesn't seem to be in here, for some reason. What brought you to write that book?

Strong:

I had taught optics at Hopkins for years. I liked what I heard myself say, and so I wrote it out. It's been a successful book.

DeVorkin:

Was it meant as a textbook?

Strong:

Yes, it was meant as a textbook. But it takes a special kind of a writer to write a textbook, and I wasn't that kind. I intended it as a textbook.

DeVorkin:

Did your wife help you with any of the writing?

Strong:

Yes she did — with grammer, punctuation, and spelling. She always said, when she typed my first book, that I was a creative speller — that some of my misspellings were so logical that she, a perfect speller, got confused. My optics book has not been used as a textbook much, if any. But, I have many reader "fans", who like its contents. And, of course, it has some very interesting appendix material by other authors. I'm writing another book now.

DeVorkin:

What is it?

Strong:

Well, my first book, Procedures In Experimental Physics was in print fof 40 years and went through 35 printings. It's still in demand because a lot of its descriptions are still valid. It had, as I evaluate the situation, an important usefulness which was unanticipated. That is, it served young fellows in determining whether or not experimental physics was to their talents, tastes and personality traits sufficiently to promise a rewarding career in it. The book I'm writing now is, in part, a lot of anecdotes about physicists: Planck, Kepler. Tycho Brahe. the Clarks. Langley Daddy Bashear, Rowland. and others. The title of the new book is Appreciation of Experimental Physics. What I'm trying to do is to get out a book that in part is a sequel to the 1938 one. and a book which will have an impact for people who want to know what experimental physics is like.

DeVorkin:

That's marvelous. In your many years as an experimental physicist, certainly the technique of designing optical systems has changed, the grating art has changed with computerized machines, and that sort of thing. In general, what would you say have been the most significant changes and trends in the grating art during your career?

Strong:

Well, I'm really not up on the grating art as it exists today, they make gratings today with lasers, — etching the grating grooves with a holographic system.

DeVorkin:

But during your time you made an advance with the aluminum on glass?

Strong:

That is the biggest advance in the grating art that I am responsible for. I also made an advance in the lapping of lead screws that is recognized in industry. I developed several techniques which are useful in precision machine tool practice. And that was a consequence of the work on ruling engines. But my work on ruling engines, in a sense, was supernumerary, because now the control of the relative position of the ruling engines components is accomplished by interferometry. Here Harrison was the pioneer.

DeVorkin:

So you feel that advancing the techniques is the trend in your work?

Strong:

I have been pleased when people have indicated to me, or told me catagorically, that they enjoyed the perspective I gave them by some of the concepts I wrote of: "primitive constructions"; "kinematical design"; "over constraint and averaging;" etc. — all in the category of techniques.

DeVorkin:

I wasn't that sure about that. Okay, do you think there's anything else we should add? I wonder if you have anything else to add that you want to put on tape at this time. Okay, well, thank you very much. This is a marvelous session. You'll be getting a transcript of this in due course. I want to put on the tape though that we're very interested in any papers, letters, correspondence with other scientists that you may have saved and we would like to know what your plans are for them.

Strong:

Well, I'm rather loath at this time, being so deep in other projects, to make a search of my papers. Is there any time limit on this?

DeVorkin:

No. there's no time limit. We just want to make sure that they're preserved.

Strong:

I'd like to preserve Plummer's minutes of the conference I had on planetary science at Hopkins. I'll get a copy of it to you.

DeVorkin:

I'd be extremely interested to know more about that. That'll be fantastic. Thank you so much.