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Oral History Transcript — Dr. Leon Chaffee

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Interview with Dr. Leon Chaffee
By Frederick V. Hunt
At faculty room of Jefferson-Leyman Laboratory
January 31, 1964

open tab View abstract

Leon Chaffee; January 31, 1964

ABSTRACT: Graduate study at Harvard University; greatest influence was Wallace C. Sabine; Ph.D. on E/M as a function of accelerating voltage supervised by Harry Moss, 1907; as corollary he developed the ďChaffee quenched gapĒ for producing continuous oscillations. Work on oxide filament in thermionic vacuum tubes, 1910; the Chaffee Gap used in wireless telegraphy experiments, 1911; mercury arc work with Pierce resulting in mercury vapor detector. World War I: torpedo detectors, double modulation, warbling the spectrum by rotating condenser, super-heterodyne; travels to France and Italy to demonstrate his transmitter. Starts first vacuum tube course in U.S. at Harvard, 1920; work on regeneration in coupled circuits, 1924; elaborate equivalent circuits, 1929; works on electronic response of retina with Bovie (first application of vacuum tubes to biophysics; continued some work of Einthoven), 1920s. In 1930s, works on stimulation of autonomic responses in a monkeyís brain (R. U. Light), and power tubes and non-linear systems; becomes chairman of Power Tubes Committee of the Institute of Radio Engineers. Also a short discussion of the invention of crystal oscillators by Cady, Pierce, and Arnold.

Transcript

Hunt:

Letís start out, Professor Chaffee with the biography. You were born in 1885, I believe in these parts, werenít you.

Chaffee:

In Sommerville, yes.

Hunt:

Was your family a scientific family?

Chaffee:

No.

Hunt:

What was your Dadís occupation?

Chaffee:

He was a chemist, and pharmacist.

Hunt:

You went to Sommerville School and eventually you turned up at MIT. Why was that?

Chaffee:

Why did I turn up at MIT?

Hunt:

Yes.

Chaffee:

Well —

Hunt:

Letís put it this way. How early did you know you wanted to be a scientist?

Chaffee:

Oh, way back in grammar school, I guess, because I was very much interested in engineering and in science. I had always planned to go to MIT. I donít know how much influence my family had, but I donít think very much.

Hunt:

So you went to MIT. and graduated there in 1907. How did you happen to come to Harvard?

Chaffee:

I took electrical engineering at MIT. When I was young, I was interested in engineering. I wanted to do practical things, deal with practical matters, but through my course at MIT. I had a growing feeling that was not what I wanted, that I really wanted to study the fundamentals of science, and particularly of physics. So, there was no question about what I should do. I was just waiting to get through with the MIT. course so that I could go to Harvard.

Hunt:

Was there a particular professor at MIT. who was a stimulus to you?

Chaffee:

Well, not a stimulus to turn me that way, but there was a particular professor who was a stimulating contact and that was Professor Harry Clifford, and he later was at Harvard. I knew him then very well and had many contacts with him.

Hunt:

He was brought to Harvard by Professor Wallace Sabine.

Chaffee:

Yes.

Hunt:

I believe he was the editor of your book, wasnít he?

Chaffee:

Thatís right.

Hunt:

What other people at Harvard did you come in contact? What are the first personalities you recall at Harvard?

Chaffee:

Wallace C. Sabine mostly, but also Professor Trowbridge who then was Director of the Jefferson Laboratory. Of course there are others who impressed me very much such as Professor Hall; Professor G. W. Pierce, Mathematician; Professor Bialy, who was in the Mathematics Department — but I think Professor Sabine was the outstanding man so far as my contact and my future was concerned.

Hunt:

You mentioned Professor Hall — weíre holding this interview in the Faculty room in the Lyman Laboratory — you will recall as I do, Professor Hall used to come in here and take a nap on that couch, in the later years of his life.

Chaffee:

I do remember that.

Hunt:

Professor Sabine was influential, wasnít he?

Chaffee:

Yes, quite so.

Hunt:

I think you mentioned to me at one time that he had helped get your appointment here after you finished your Doctorate Degree.

Chaffee:

Iím sure he did. I donít know the internal workings of a department at that time, as I was a student, but I am sure that he was the one who advanced me.

Hunt:

Professor Lyman was here then, too, wasnít he?

Chaffee:

Yes he was.

Hunt:

Do you recall any others?

Chaffee:

Mr. Pierce was here, G.W. Pierce.

Hunt:

Now, what did you do your Doctorate thesis with?

Chaffee:

I did that for some reason, under, which I donít know, under Professor Harry Moss, and he was a chemist, or rather interested more in chemistry, still in the Physics Department. As I say, I donít know why I chose him, but he was my research director.

Hunt:

Did he suggest the problem that you picked?

Chaffee:

No, he didnít. I picked my own problem.

Hunt:

What did you pick first? What did you start to do for this thesis?

Chaffee:

My main objective was to measure E over M, of the electron, as a function of the accelerating voltage; to obtain the change in mass due to velocity change, the relativistic change.

Hunt:

Did you bring this off?

Chaffee:

Well, I didnít at that time. I set up the apparatus for doing it which consisted mostly of a cathode ray oscilloscope, and that was operated on the 40,000 volt storage battery which was then installed in the Jefferson Laboratory. For my method, which I believe was a new method of measurement of E over M; I needed a source of continuous oscillations of two meters wave length. I searched the literature and the practice to find such a source, and could not find it. I then set about to make a method which would serve the purpose of continuous oscillations, and I succeeded in the form of a special gap.

Hunt:

This is the famous Chaffee-quenched gap.

Chaffee:

Yes, it was the gap between aluminum and copper terminals in atmosphere of hydrogen. It did produce continuous oscillations of any wave length easily up to two meters wave length —

Hunt:

This is why itís called quenched gap. What was quenched about it?

Chaffee:

Well, I think thatís a misnomer. It was quenched in the sense that it did not oscillate, it allowed the current to go through in pulses and the pulse was cut off by, I suppose, the action in the gap, so that it did not produce trains of oscillations as ordinary gaps did.

Hunt:

These devices always had large fins, this was —

Chaffee:

This was water cooled.

Hunt:

The temperature control was important in the quenching, wasnít it?

Chaffee:

Yes.

Hunt:

Now, this produced continuous oscillations, at this then high frequency for the first time, didnít it?

Chaffee:

I believe so, yes. I think there was that one gap which was purported to give continuous oscillation — it was the Peukert, German invention, but that I tried, but could get no continuous oscillations from it.

Hunt:

What power level did this operate?

Chaffee:

Oh, 50 to 100 watts, or perhaps more.

Hunt:

Pretty respectable power.

Chaffee:

Yes.

Hunt:

Now, with this gap you could have finished the E over M experiment, couldnít you?

Chaffee:

Yes, I could have. There were two reasons for not doing it at that time. I got so interested in the properties of the gap and its operation that I devoted my Doctors thesis to that as an investigation of the operation of the gap. The other reason for not continuing at that time was that 40,000 volts was hardly adequate to produce a good change in the value of E over M, and there was planned, at that time, to build a larger battery of 100,000 volts. The money for that was given by Dr. Blackwell, a former student. So, I thought I would wait for that higher voltage, however, the battery was not built for a considerable time, longer than first anticipated, into the Ď20ís.

Hunt:

Were the mechanical alternators of Fessenden well-known at that time?

Chaffee:

A little later, I believe, but they were very low frequency devices. They would not go up much higher than 10 or 20, 50,000 cycles.

Hunt:

This was two meters —

Chaffee:

Three meters is a million, isnít it?

Hunt:

Itís then 150 megacycles.

Chaffee:

Yes.

Hunt:

You mentioned the cathode ray oscilloscope. You didnít call it that in those days did you?

Chaffee:

No. What did they call it? They called it the Braun Tube, and I had a Braun Tube imported from Germany which I used, but then I constructed my own Braun Tubes for this E over M experiment, or rather had them constructed for me.

Hunt:

That was later?

Chaffee:

Oh, that was later. Well, I had them then, too, because I did try this out at that time with the 40,000 volts.

Hunt:

So you did it more or less — you carried on this experiment. Itís Just that the voltage was too low to get a demonstration of the relativistic effect.

Chaffee:

I knew I couldnít get as good a result as I wanted.

Hunt:

The ones you made, was this the occasion for your first go at monoxide thermionic emitter.

Chaffee:

Yes.

Hunt:

Letís date this. You attended Harvard, 1908-1911 and you got your degree in 1911. This gap must have come around 1912.

Chaffee:

Yes.

Hunt:

Had you done this oxide filament by the end of your thesis?

Chaffee:

No. This came after the thesis. Iíd say about two or three years after the thesis.

Hunt:

How did this oxide filament thing look? What was this device?

Chaffee:

I mounted a strip of platinum, about 1/16th inch wide, which was the heater, and on the center of this strip of platinum was a dot of oxide, so that the emission came only from the dot.

Hunt:

What kind of oxide?

Chaffee:

Calcium oxide.

Hunt:

What gave you the idea of using calcium oxide?

Chaffee:

I donít remember, but I think I knew at that time, that oxides did emit.

Hunt:

Do you know whether anybody else had used the oxide emitter before that?

Chaffee:

I donít think so — not on the cathode ray tube. Now, as to whether they were used in thermionic vacuum tubes —

Hunt:

The Wehnelt cathode —

Chaffee:

The Wehnelt cathode —

Hunt:

That was used in the tubes of 1914.

Chaffee:

I just canít be sure. I donít remember.

Hunt:

So, you had a gap in 1911, and you had a source of continuous oscillation. What else did you do with it? What did you do with it when you abandoned E by M waiting for voltage?

Chaffee:

Well, as a source of continuous oscillation, I immediately thought it would be applicable to wireless telephony. G.W. Pierce joined me in two-way experiments and in carrying on tests of telephoning between here and his house, between here and Gloucester, Mass., and various other places. We modulated by simply putting a microphone in the antenna.

Hunt:

A carbon microphone?

Chaffee:

Yes, a carbon microphone, with perhaps one ampere in the antenna. Something of that sort.

Hunt:

What kind of an antenna did you use for the experiment?

Chaffee:

I donít remember in detail, but a vertical wire, probably. Probably at G.W. Pierceís house it was just a wire from the roof.

Hunt:

Now Cruft Laboratory was built in 1914, and it had the big tower. Did you use the tower for this source?

Chaffee:

Yes, a low antenna on the towers, I believe.

Hunt:

You told me a nice incident about a student that eavesdropped on your telephony experiments.

Chaffee:

I didnít see the student, but G.W. Pierce tells this story that a student who was living in Hallworthy Hall, in one of the dormitories, was lying on his couch with the earphones on his head listening to amateur telegraph signals, and suddenly he heard a voice which was then not common. He ran over to G.W. Pierce and said ďSomething must have happened. I think perhaps a telephone wire fell over my antenna.Ē

Hunt:

So, this is 1911-1914 vintage — somewhere in there, did you get connected with Hammond at that time?

Chaffee:

Yes, I think around possibly 1915.

Hunt:

Before that you were involved with Prof. Pierce in the mercury arc.

Chaffee:

Yes, he was consulting engineer for John Hays Hammond, Jr. of Gloucester. John Hays Hammond was occupied in steering torpedoes by radio, and G. W. Pierce was helping him in that work and had suggested and used a detector comprising a mercury vapor lamp with a grid and a plate, and then the mercury pool for the emitter similar to a triode except it was a triode, except, of course, there was mercury vapor. This acted as a detector.

Hunt:

Professor Chaffee, was this sealed off at atmospheric pressure?

Chaffee:

Oh no, this was activated. All the air, which is as much as possible, was taken out, but there was still mercury vapor in the tube. Hammond and he got into some controversy about the patent situation regarding that, and G.W. Pierce then took me down to Gloucester to see the work going on down there, and he withdrew from further work so that I took up the work of helping Hammond in his radio-controlled torpedo work. I did a good deal of work on stabilizing and improving the mercury vapor detector, at first.

Hunt:

Was this related to the Cooper-Hewitt lamp? Do you think this is where Pierce got that idea, or vice versa?

Chaffee:

Pierce sold his patent eventually to Hewitt, and out of this came the Cooper-Hewitt lamp. This mercury vapor lamp development was interesting in two other respects; one, it was the basis for the thyratron development, and Pierce got into some patent controversy on that score. The other was an incident that occurred in the early 1930ís. The Western Electric Company got involved, in Canada, in an interference suit on the talking movies. In one of Pierceís patent disclosures, he had shown this mercury vapor lamp with the discharge modulated by a microphone signal, and Western Electric in defending their suit — by this time they had acquired the patents, and Western Electric came up, took some of Pierceís old apparatus that he had salvaged, connected it up with a microphone, recorded sound on a film, and used it to defend their suit in Canada. So, Pierce, one morning when he came in said, ďI just discovered that I invented the talking movies twenty years ago and didnít know it.Ē

Hunt:

Well, you then got involved in the torpedo business and this continued up until the U.S. involvement in World War I. Tell us what happened in that interval?

Chaffee:

Well, World War I began in 1917 — previous to that we had given up the mercury vapor lamp as the detector. I had worked on detectors involving gas, regular triodes with a small amount of atmospheric gas in the tube. That acted as a detector, and a very sensitive detector because of the kinks in ionization caused by ionization potential. I did a great deal of work on developing these on the pumps here in the laboratory, and applied them both to the torpedo work and also to a communication system. About that time, the Signal Corps became interested in some work that was being done at Hammondís Laboratory on a secret and interference less communication system. They were interested in it as a possible application in the front-line trenches. This new communication system which involved not only the particular detector that Iíve spoken of, but also of double modulation involving circuits somewhat similar to the super heterodyne. As to just who first devised the circuits, I donít know. It may have been Hammond, and it may have been me, but Iím not sure at all about that.

Hunt:

Was Hammond much of a technical man?

Chaffee:

No, he did very little work himself. We never saw him at the bench doing any work. He was mostly a thinker.

Hunt:

An idea man.

Chaffee:

Yes, an idea man.

Hunt:

You mentioned circuit. There are the hardware circuits that did the receiving, but there was also the concept of the double modulation. Remind me how this double modulation works.

Chaffee:

Well, the, process was to modulate by sound, by voice, or by signals — a dot and dash signal — either one, a 20,000 cycle tone. When this 20,000 cycle tone was used to modulate the carrier, which may be up in radio frequencies, the signal could be received —

Hunt:

There was a transmitted signal, was an RF carrier and two 20 kilocycles sub-carrier side band each of which had its own audio side bands attached. Chafee: Thatís right. Now this was not secret because a person with a simple herodine could beat the side band — one of the side bands, and receive a message. So, to prevent that, we warbled the whole spectrum by a rotating condenser in the antenna.

Hunt:

It was the RF carrier that was warbled.

Chaffee:

Not only the carrier, but the sidebands too. It carried the side bands with it, so that that messed up anybody, any reception from beating. In order to receive it then, had to first receive the radio go through a 20,000 cycle intermediate frequency — of course with the heterodyne to beat down to the 20,000 cycle, then receive the message.

Hunt:

You had to have a radio frequency band that would include the excursions of the RF carrier, and then this would carry the rest of it in.

Chaffee:

Yes.

Hunt:

Very ingenious. How about synchronizing the detection with the modulation of the carrier?

Chaffee:

They were always the same distance apart, because the whole thing was warbled, so that the warbling tone did not appear in our reception.

Hunt:

Was that concept of the warble yours or Hammonds?

Chaffee:

That was mine, Iím sure of that. We were sent over to France with this system to demonstrate to the AEF, and that we did.

Hunt:

You spent some time in Italy, too?

Chaffee:

Yes, we also demonstrated it in Italy with Professor Varni in Rome and it was remarkably successful in that the Marconi engineers were invited down to the laboratory, the Varniís Laboratory, where our transmitter was set up. They were in another room, and they had all the apparatus they could muster to see whether they could pick up the message. Our message was put out on an antenna, and we went out on a station wagon with the receiver — say twenty miles out, and received that they were unable to pick it up, which attested to the secrecy of it.

Hunt:

I think I recall the name Varni in connection with some of the early experiments on modulation.

Chaffee:

Yes, he had a detector on modulation.

Hunt:

Iíd like to go back just a minute to the installation in France. Was there a Frenchman by the name of Ferriť?

Chaffee:

Yes.

Hunt:

What was his role in that organization?

Chaffee:

Well, I didnít meet him. I really donít know. I remember the name very well.

Hunt:

Dr. Le Corbeiller worked closely with Ferriť in the War. He has talked to me about that.

Chaffee:

I did not meet any of the French, only the American representatives. There was General Russell at that time over there in command of the AEF, and Edwin Armstrong —

Hunt:

Armstrong was in the group to whom you demonstrated in France.

Chaffee:

Yes. He was in charge of the Paris laboratory at that time of the Signal Corps. And your demonstration occurred just before Armstrong made his announcement of the super heterodyne receiver.

Chaffee:

Yes.

Hunt:

Was there a man by the name of Labe there, a Frenchman?

Chaffee:

Well, I remember the name, but I didnít see him.

Hunt:

It seems to me that his name has come up in regard to the super heterodyne, and I was wondering if there might be any relation between Labe and Armstrong.

Chaffee:

I think Dr. Le Corbeiller is in New York now, and I would suggest that you ask him about that.

Hunt:

But letís try to pin down the relation between this method of modulation and the super heterodyne. In the super heterodyne you have a local oscillator which beats with the carrier, and then you amplify at the different frequency, and it is the amplification that affects different frequency which is one of the great virtues of the super heterodyne. Now, in this case you can amplify at the 20 kilocycle sub-carrier. This has the advantages so far as the receiver is concerned of the super heterodyne, and it differs only in that instead of supplying the sub-carrier locally, you transmitted it.

Chaffee:

Thatís right.

Hunt:

And in its answer, I suppose you were going to be beat by it, because itís less efficient for the transmitter to transmit that power than to supply it at the local receiver.

Chaffee:

Yes. There is certain advantage, as far as the super heterodyne. On the other hand, there is one slight difference here too. In our case, we modulated the intermediate frequency, the 20,000 cycles. In the ordinary super heterodyne, the carrier wave would be modulated. But there is a close connection.

Hunt:

By the time you were doing this, you were using vacuum tubes?

Chaffee:

Yes.

Hunt:

So you had to work out some theory for these vacuum tubes, and you did didnít you?

Chaffee:

Yes.

Hunt:

This is a lead-in now for the aftermath of this war-work. What came next?

Chaffee:

After the War, I guess I —

Hunt:

You came back and you had a lot of notes on how the vacuum tubes had worked.

Chaffee:

Yes. Let me recall. I —

Hunt:

Iím trying to lead you in this first course in vacuum tubes offered in 1920.

Chaffee:

Thatís true. I did introduce a course in vacuum tubes in 1920, and I think it was 1918 that I had been abroad — well, that was coming back from 1918, of course — coming back from there after the War because the Armistice was just signed in 1918, and I came back. On the ship coming back, I did write out a theory regarding the vacuum tube, because none was available at that time, and introduced the course in vacuum tubes here in 1920.

Hunt:

As far as you know, is this the first course ever offered in an American college?

Chaffee:

As far as I know, and I think it was so for a number of years, too.

Hunt:

Probably in any college?

Chaffee:

I think so. MIT started vacuum tubes considerably later because one of their students came here and took the courses here, and then went back and introduced it.

Hunt:

Who was that?

Chaffee:

Bolds, Edward Bolds.

Hunt:

I wonder if I could go back just a minute. The work which you were doing with Hammond was under contract as private individuals with the Government?

Chaffee:

That is right.

Hunt:

It wasnít within the contract of the Signal Corps?

Chaffee:

It was a Signal Corps contract.

Hunt:

It was the Signal Corps contract, but was it outside the Government? It was a private contract with the Signal Corps to do its work?

Chaffee:

Yes. I was a private consultant to Hammond. But previous to that, a lot of the work was done previous to this contract with the Signal Corps. When Hammond was working individually on steering torpedoes, and that work he did and had, at one time later, a contract with the Navy to do that work. He succeeded with it, steering the white head torpedo by radio.

Hunt:

We were speaking the other day about the equivalent plate circuit theorem. Van Der Waals credits this to you about 1913.

Chaffee:

I think that was in existence before —

Hunt:

I always thought that was yours.

Chaffee:

I didnít know it at the time.

Hunt:

Iím glad our conversation — you discovered this independently.

Chaffee:

Yes, thatís right.

Hunt:

We had a new vacuum course in 1920, and now within a year or two you get diverted into a new interest.

Chaffee:

You mean the eye work?

Hunt:

Before we pick that up, I wonder if I could go back just to the matter of the equivalent circuits. What led you to develop this?

Chaffee:

I had no theory. I knew no theory of the vacuum tube. I had not read any. I donít think any was easily available at the time I returned from abroad. Van Der Waals book didnít appear until 1920. I thought I would work it out myself, which I did.

Hunt:

Did you approach this in terms of experiments, or in terms of theory?

Chaffee:

In terms of theory, but of course, I had experimented with it, and made them in the laboratory. I made many of them, both oscillators and detectors. Although I think the oscillators came a little after that. I did mostly detector work at that time.

Hunt:

When you applied voltages to two ends of the vacuum tube and measured two currents, you very quickly need some kind of theory to guide you in handling all these variables.

Chaffee:

Yes. I wish I had preserved my notes at that time, but I have never found them. It would be interesting to compare them with — but I was doing this in anticipation of them being put in a course as I was planning to put that course in.

Hunt:

We went over one bit of activity you did in this 1915 period. You got into this with Pierce, or was it Pierce that interested you in current relations in coupled circuits?

Chaffee:

Pierce had done a very — some preliminary work in coupled circuits, but I got much more interested. His was mostly free oscillations in coupled circuits, and I got more interested in the forced oscillations as well as the free oscillations, and wrote some papers on that.

Hunt:

In 1916 you wrote papers on that?

Chaffee:

Yes.

Hunt:

There are interesting threads of continuity. You did this in 1916, and then you had your vacuum tubes, and now early in the 1920ís you do this monumental job on regeneration in coupling circuits. This, sure strikes a chord in you, in your memory?

Chaffee:

Yes, I spent a good deal of time on that. I worked it out. It was an interesting theory, but Iím afraid the practical value of it was —

Hunt:

This paper was published in 1924, and I appeared on the Harvard scene in the fall of l925, so itís still fresh in your mind, and I recall very vividly your teaching of this subject and laboratory experiments that you had arranged in which all these weird variations of current were tooting, went down the laboratory, and by golly, it worked that way. The laboratory experiment was a fine demonstration that the theory really worked. Wasnít this applied in the design of the sets of the time?

Chaffee:

I imagine so.

Hunt:

Donít you remember the Browning-Drake receiver, with that tickler coil?

Chaffee:

Yes. Also there were transmitters that were put out by the Cutting and Washington people who bought my patent on the gap, and they were putting out transmitters with the gap as a source of oscillations.

Hunt:

Well, you had this regeneration in coupled circuits in 1924, and three years later you do the work on the voltage detection co-efficient. I suppose in that period is when you went from the linear to the non-linear, but you have a throw-back to the linear in 1929 with this job on the equivalent circuits. These are now more elaborate equivalent circuits in which you take into account the — which you deduce the input and output admittances. I made a continuity appear here. Was it continuity in your mind, too?

Chaffee:

It was a natural sequence, I guess, thatís all. I donít know if I understand exactly what you mean by continuity.

Hunt:

I think what I mean is your devotion to vacuum tubes and the most pressing problem in vacuum tubes was continuous.

Chaffee:

Yes, that is true. It has been practically all through life.

Hunt:

And in one sense that jumps on to with the admittance with the throw-back to the linear, but then you go non-linear again with your techniques for analyzing the performance of high power tubes.

Chaffee:

Of course, detection is non-linear, also.

Hunt:

Well, then this is a continuity of work on vacuum tubes, but as you say, continues right on. But still in the early 1920ís, you get a distraction with the electric response of the retina. This one sort of interleans and comes along for a period of almost ten years. Tell us about this. How you got into it, and how it developed.

Chaffee:

That resulted from a conference that I had — I donít know the exact date, but before this work began with Professor Bovie who was then in the Medical school. He was a Professor of Biophysics — I donít know whether he was Professor — I think he was only Doctor. He got me interested in the eye, and induced me to go in with him in experimental work on the electrical response of the retina. Although this was far afield from my primary interest, being biological, it nevertheless was a wonderful place to apply the vacuum tube. Now Einthoven had previously measured the response of the retina of a frog using the whole eye by putting electrodes on carrying them to an Einthoven Galvanometer with no amplification. That was the initial work, and I think about the only work up to that time that had been done on the eye. I emphasize, he did not cut the eye in two. He used the whole eye. We set up the apparatus over in the Peter Bent Brigham Hospital, where Bovie was, at that time stationed, and with a two-page amplifier using Western Electric tubes, we got a considerable response from the retina over and above what theyíd ever gotten before. I continued that work by — we cut the eye in two, and set the optic nerve on a pad which was one terminal going to the amplifier, and the other electrode was consisted of a thin thread of cotton soaked in ringer solution which touched the retina inside and lightens, of course, as shown on the retina, and we measured the variation of intensity with intensity of light, and with the change of color, and various aspects of that. I think there were several students who followed in taking up the work under my direction. I donít know. There were some eight or ten papers, I guess.

Hunt:

I was going to say, you brought in quite a few people. Edwin Sussquiss, Meservy, C. E. Keeler, and there was another colleague you had in the beginning of this work by the name of Hamson.

Chaffee:

Miss Alice Hamson had been a student at Radcliffe where I had given a course in Physics, and after graduation, she became my assistant in this work and manipulated the apparatus.

Hunt:

Sheís been your assistant ever since?

Chaffee:

Yes. Sheís my wife now. Married her in Ď24,

Hunt:

That was the date of the first paper.

Chaffee:

Was it?

Hunt:

Yes.

Chaffee:

Well, the work was done long before that.

Hunt:

The paper was done in 1923. No 1922. You used your assistant for two years before you married her.

Chaffee:

Yes.

Hunt:

Was this one of the first applications of the vacuum tube to instrumentation in Biophysics?

Chaffee:

In Biophysics I think it was.

Hunt:

You couldnít say in Physics, in general?

Chaffee:

No.

Hunt:

In general, because amplifiers were too eagerly wanted for too many things. For instance, the use of the vacuum tube — the use of the amplifier for the measurement of voltages — about when did that begin?

Chaffee:

Thatís hard to say.

Hunt:

When you say measurable voltages — if you used a vacuum tube for a transcontinental telephone, youíve measured some voltages. Now I think in the hands of the laboratory rather than commercial. Well, it was used for the condenser microphone in sound in 1919, so that every scientist used this as a voltage measuring tool, very early.

Chaffee:

I think so. Yes.

Hunt:

These tubes didnít have a very high input resistance, did they that is in the early Ď20ís?

Chaffee:

Pretty high. These were Western Electric tubes. They were apt to be a little bit gassy, but they were fairly good, and I had to construct a DC amplifier. That was the more difficult thing, because I wanted to preserve the shape of these pulses and I could not have any condensers in the circuit. I did this by balancing storage battery voltages against drifts. That worked out pretty well.

Hunt:

You had one other fling about the middle 1930ís with Biophysics.

Chaffee:

Oh yes, with Dr. Light. Dr. Light was at Yale University at that time, and he was interested in brain response. He heard of me, and interested me in devising a means of stimulating a monkeyís brain electrically without attached wires. He was interested in that I mentioned in studying the autonomic responses of the monkey by strong stimulation of the inner part of the brain that is down between the two halves (?). So, what he did was to operate on the monkey, and insert under the skull, a small coiled wire about an inch in diameter of many turns. One was a neutral electrode, just connected to a plate. The other was a wire thrust down into the brain where he wished to stimulate. My contribution only was in devising a means external to the cage of inducing a voltage in this little coil. This consisted of discharge from using thyratrons and a large coil around the cage so that we could produce pulses in the large coil which then produced pulses in the smaller coil and cause the stimulation.

Hunt:

There were lively times around the Cruft Laboratory, at that time when they brought a monkey into try this scheme out. This was not the kind of normal apparatus we used at Cruft.

Chaffee:

It was my understanding that Cady had invented or discovered the properties of a crystal as a resonator. In other words, he used it as a very sharp tuned circuit. Whereas Pierce, as is my recollection, was the first one who actually made the crystal oscillate by connecting it into a vacuum tube circuit. I think Cady admits that, because the patents reflect that difference. Cady had patents on the resonator; Pierce took out patents which were not challenged by Cady on the crystal oscillator. Now where does Arnold come into this? I donít know whether he comes into this?

Hunt:

That is a rather long story, and as I mentioned before, there are these black and white pictures of 4.0 Arnold. Perhaps we can come back to that later. I dug into this crystal oscillator story pretty carefully in the history section of my book on electro acoustics and I reviewed my own text before I spoke too much on that. That was a sticky story.

Hunt:

I think Professor Cady agrees completely with your description of it. In fact I got some of it from him. I consulted with him before it was printed. In fact, I sent him a copy of that part of the manuscript and had his comments before it was final. I think he does agree with it. Well, shall we go back to the power tubes, early 1930ís? Weíre tracing a logical development. You did the input circuits with the input admittances of triodes, and this pretty well dried up the linear, the analysis of linear behavior. Then, tell us the story about your involvement with power tubes.

Chaffee:

I donít know that I can recall just which started my interest in power tubes, except it probably was a natural sequence. I became intensely interested in non-linear systems. I wrote up some mathematics for non-linear systems, and the power tube, of course, is a perfect example of a non-linear device. I donít know I just naturally went over to power tubes after the smaller tubes.

Hunt:

Were there power tubes in production at this time?

Chaffee:

Oh, yes.

Hunt:

How big would they be? How many watts?

Chaffee:

The very first one, I think, was probably the Western Electric ones, about 30 watts. They were used in the transatlantic telephone.

Hunt:

Tubes had gotten big by this time.

Chaffee:

Yes.

Hunt:

They were sleeper copper glass seal in the water cooled tubes so that power was available then.

Chaffee:

Yes, they were available, and I was Chairman of the Power Tubes Committee of the IRE at that time. I donít know if that has any great importance, but Morenself (?) of Westinghouse Company was on that Committee at that time, and he and I were competitors in this theory —

Hunt:

That was late in the 1930ís, wasnít it?

Chaffee:

Yes.

Hunt:

Let me go back a little further on that. There was a fundamental concept that a power tube with an oscillator or power amplifier was efficient when the maximum current was delivered when the plate voltage was lowest. I remember your teaching this. Have you any ideas when that concept of the control of the efficiency grew up?

Chaffee:

I couldnít place that. I have no way of dating that.

Hunt:

It might have been Princeís analysis.

Chaffee:

Prince? I donít remember the gentleman.

Hunt:

General Electric.

Chaffee:

I donít remember. I donít know Prince. At any rate, I was very interested in methods of showing how and analyzing the operation of power tubes, and devised a scheme of testing and explaining. The Harmonicon analysis was one method.

Hunt:

Weíve passed over one item that Iíd like to put back in the sequence. Way back in 1911, we left that E over M experiment. When did you revive this?

Chaffee:

One of my students at Radcliffe, who came to me as director of her research for a Doctorís degree, wanted a problem, and I gave her this problem of reviving the measurement of E over M, which she did. This was Charlotte T. Perry, who later married professor Phillips of MIT. At that time then the 100,000 volt battery was available, and we just went on with the original plan of measuring it using my, at this time, lay vacuum tube as a source instead of my gap, because vacuum tubes were then available for producing the oscillations.

Hunt:

But the method she used —

Chaffee:

— was the method -ó

Hunt:

— of your 1909-11 method. So there was nothing wrong with the method. You just needed 20 more years of apparatus development. It ought to give you some satisfaction to have that measurement finally made.

Chaffee:

Yes, it was with fairly good results, too, as it lines up among the various values of the E over M.

Hunt:

How basically did this method work?

Chaffee:

It timed the passage of an electron from one set of coils to another set of coils which was spaced perhaps 1 1/2-two feet apart down the cathode ray tube. The same oscillations excited the deflecting coil, both deflecting coils which deflected the beam transversely. The idea was that by rotating one coil with respect to the other, the deflection could be made a circle, and then from the angle of rotation and the frequency, you got the value of E over M.

Hunt:

Was this R F timing method?

Chaffee:

Yes, it was.

Hunt:

Where you reduce the velocity measurement to a frequency measurement, to a frequency and distance measurement? You can hardly do better in measuring velocity.

Chaffee:

Thatís right.

Hunt:

Well, weíve come to the end of the 1930ís, and there was a war in sight. This warped all of our lives. Tell us how it warped yours? I wonder if I may interrupt this