My work with Millikan on the oildrop experimentHarvey Fletcher Citation: Phys. Today 35(6), 43 (1982); doi: 10.1063/1.2915126 View online: http://dx.doi.org/10.1063/1.2915126 View Table of Contents: http://www.physicstoday.org/resource/1/PHTOAD/v35/i6 Published by the American Institute of Physics. Additional resources for Physics TodayHomepage: http://www.physicstoday.org/ Information: http://www.physicstoday.org/about_us Daily Edition: http://www.physicstoday.org/daily_edition

Harvey Fletcher soon afterhis wedding in September 1908.

(Photograph provided byStephen Fletcher.)

My work with Millikanon the oil-drop experiment

In this personal reminiscence the late author recounts hisexperiences as a graduate student in the Ryerson laboratory in Chicago and

his contribution to the determination of the electron's charge.

Harvey Fletcher

Lorena (Chipman) and I were marriedon 9 September 1908. Soon after weleft by train for Chicago. On arrivalthere, we found a small apartment nearthe University.

My first problem was to get admittedand registered in the graduate school. Iwent to the admission authorities andpresented my credits. [Fletcher hadtaken three years of college work atBrigham Young University, which wasat that time sufficient for a BS degree.]They glanced at them and said it wouldtake a little time before they could giveme a definite answer. They made anappointment for four or five days laterwhen I should come back. In the mean-time I had become acquainted with

Harvey Fletcher (1884-1981) directed acous-tical and, later, physical research at Bell Labo-ratories from 1925 to 1952, developing hear-ing aids and stereophonic equipment. He alsotaught at Columbia University and headedresearch at Brigham Young University.

Professor Millikan and others of thefaculty of the physics and mathematicsdepartments.

When I went back to the admissiongroup I got the sad news that I must dofour years of college work at Chicagobefore I could enter the graduateschool. This was a great blow to me.After a sleepless night I decided to talkto Millikan about admissions. At thattime he had just been made an assis-tant professor and seemed to be a verylikeable fellow.

He indicated a way out for me. Hesaid I could enter as a special studentand select the courses a first-year grad-uate student usually takes. If I passedthem successfully, the admissions com-mittee might reconsider my entranceinto the graduate school. I told him Iwas sure that I could. As a matter offact, I had already taken courses simi-lar to some of these at Brigham Young.So through his help I was able to enteras a special student.

The courses were not difficult, and Ipassed them all with high gradesamong the top in the classes. With thisrecord I went back to the admissions

committee, and they decided to let meenter the graduate school as a candi-date for the doctorate with the condi-tion that I make up one year of under-graduate college work at Chicago,preferably in those lines in which I wasdeficient, such as history, English, for-eign languages, sociology.... I thusspent three full school years and twosummers at Chicago and graduated in1911. I was as well, if not better,prepared in physics and mathematicsthan any of my classmates who hadgraduated from the College at Chicago,but I was below them in my knowledgeof subjects in the general educationalfield.

I had to borrow some money to com-plete my first year of graduate work.After that, through the influence ofMillikan, I was able to get work in theUniversity that paid enough to defraymy school and living expenses for theremaining two years. During the sec-ond year I was given a job teachingscience to high school students in theCollege of Education. I cooperatedwith other members of the faculty tomap a general science course that

0031-9228 / 82 / 0600 43-05 / $01.00 © 1982 American Institute of Physics PHYSICS TODAY / JUNE 1982 43

would be suitable for boys and girls ofthat age. . . .

Also, that year I took charge of lan-tern projectors for various classes. Ireceived a dollar for each lecture. Thistoo helped out my finances. It was atthe beginning of this second year [1909]that I went to Millikan to see if he couldsuggest a problem upon which I couldwork for a doctor's thesis in physics.He was a busy man, and I had a hardtime making an appointment with him.Finally, he told me to come down to oneof the research laboratories where heand Professor [Louis] Begeman wereworking and he would talk to me.First he and Begeman showed me theresearch work that they were doing onthe electronic charge, and reviewed thework that J. J. Thompson and E. Re-gener had been doing along this line inCambridge, England.

They had arranged a little box hav-ing a content of 2 or 3 cubic centimetersthat was fastened to the end of a mi-croscope. A tube was attached from anexpansion chamber to the box. Byopening suddenly a petcock, a suddenexpansion of the air in the box caused acloud of water vapor to form. Whenviewed through a microscope this cloudwas seen to be composed of a largenumber of tiny water drops. The dro-plets would soon fall from the top to thebottom of the box under the influenceof gravity. A conducting plate wasarranged at the top and another one atthe bottom of the box so that an electricfield could be imposed.

When an electric field was turned on,it would retard the fall of some dro-plets. They were trying to make thefield just right so that a selected dropletwould be suspended in the air betweenthe plates. From the speed of the

Apparatus for the oil-drop experiment at Caltech in the early 1920s. (Photograph courtesyCalifornia Institute of Technology Archives and AIP Niels Bohr Library.)

droplet, that is the fall speed, and theintensity of the field to stop its fall, onecould calculate the electrical charge onthe droplet. This was essentially re-peating the experiment that Regenerdid in England. However, the waterforming the droplet evaporated so fastthat it would only stay in view for about2 seconds, so it was difficult to get morethan a rough estimate of the charge.

We discussed ways and means ofgetting around the difficulty, and Ithink we all agreed that we shouldhave a droplet that did not evaporate ifwe could get it small enough and couldcontrol it. Mercury, oil, and two orthree other substances were suggested.In a discussion of that kind, it is rather

difficult to be sure who suggested what.I left with the impression that I hadsuggested oil for it was easy to get andto handle. However, in his memoirsMillikan said he had been thinking ofthis before this conference. Of course, Icannot say yes or no to that, but I doknow what happened after this confer-ence.

Professor Millikan said to me,"There is your thesis; go try one ofthese substances which will not evapo-rate."

To build an apparatus like they wereusing would take considerable time. SoI decided to make a crude setup in thelaboratory and try it before designingan elaborate one. I went out to the

Source of the storyLast year Mark B. Gardner, of Spanish Fork,Utah, wrote an obituary of his long-time friendand co-worker, Harvey Fletcher, for PHYSICSTODAY (October 1981, page 116). In thecourse of correspondence with Gardner, welearned that Fletcher had left him a manuscriptautobiography that included an account ofFletcher's work in the celebrated oil-dropexperiment for which his thesis adviser, Rob-ert A. Millikan, won the Nobel Prize in 1923.Fletcher had instructed Gardner to publish themanuscript only posthumously, so it would beclear that Fletcher had no personal interestmotivating its publication. In fact, Gardner toldus that Fletcher was deeply grateful to Millikanfor the many kindnesses he accorded him andfor the friendship that lasted throughout theirlifetimes. He did not want in the least totarnish Millikan's reputation. At our request,Gardner sent us the manuscript and obtainedthe consent of Fletcher's family to have itpublished.

Fletcher's account fills a gap in Millikan'sotherwise extensive deceptions, in his booksand his Nobel Prize Lecture, of the sequenceof experiments he undertook to determine the

magnitude of the charge of the electron. Itrelates how and by whom the apparatus forthe final phase of the experiments, that usingoil drops, was devised. The matter is all themore significant because of the importancethat Millikan himself saw in the details andmechanism of the experiment. In his NobelLecture he said that "my own work has beenthat of the mere experimentalist whose mainmotive has been to devise, if possible, certaincrucial experiments for testing the validity orinvalidity of conceptions advanced by othersregarding the unitary nature of electricity."Shortly afterwards came the remark, "Thesuccess of the experiments first performed in1909 was wholly due to design of the appara-tus, i.e., to the relation of the parts.... Scarce-ly any other combinations of dimensions, fieldstrengths, and material could have yielded theresults obtained."Fletcher came to Chicago and to Millikan at atime when the existence of the electron wasbecoming widely accepted by experimenta-lists as more than a heuristic device. Only twoyears before, J. J. Thompson had published apaper reporting measurements of the con-stant charge-to-mass ratio of cathode rays,which, in Millikan's words, "put together, in a

matchless manner, the evidence for the viewthat the cathode rays consist not of etherwaves . . . but rather of material particles car-rying electric charges, each particle possess-ing a mass of about V1Ooo of that of the lightestknown atom." Values were sought for themagnitude of the electron's charge. Earlydeterminations were averages of very manyhypothetical individual charges; they were in-direct measurements at best, according toGerald Holton in his essay on Millikan in TheScientific Imagination.

Millikan and his student Louis Begeman initial-ly used such a method, one devised by H. A.Wilson, in which clouds of water droplets wereproduced in an expansion chamber betweenparallel horizontal plates of a charge condens-er. This method assumed that Stokes's lawheld for the droplets, presupposed that eachdroplet formed on a singly charged ion, andignored the effects of evaporation. The re-sults that Millikan and Begeman produced,falling within a smaller range of values of ethan those of Wilson, were only tentative.

Millikan attempted to improve his results byeliminating the error from evaporation. He

44 PHYSICS TODAY / JUNE 1982

drug store that afternoon and boughtan atomizer and some watch oil. ThenI came back to the laboratory and setup the following apparatus:

First, an arc light with two condens-ing lenses in front of it was set up. Thecombination made a bright beam oflight. The experience I had with pro-jection lanterns for lectures made itpossible to get this together very quick-ly. I then used the atomizer and squirt-ed some oil spray so that it fell throughthe beam of light. The light made thesetiny drops of oil look like tiny stars.This indicated this part of the experi-ment would probably work. Next, Iwent down to the student shop andfound some brass sheets about one-eighth of an inch thick. From them Icut two circular plates about 20 centi-meters in diameter. I soldered a stemonto each one so that they could be heldby an ordinary laboratory stand withclamps. A small hole was then bored inthe center of the top plate. Next, theplates were set up horizontally about 2centimeters apart. In this first setupthe air between the plates was notenclosed. So I moved the stands hold-ing the two plates over into the beam oflight. I then put a large cardboardbetween the light and the plates andcut a hole just large enough to permit abeam of light to go between the plateswithout touching them. Next, I found acathetometer, an instrument common-ly used around a physics laboratory,and placed it so the telescope on it couldbe turned and raised or lowered untilits line of sight went between the twoplates at about 120° from the directionof the light beam. The distance fromthe telescope to the plates was about 1meter. I then tried out the apparatus.I turned on the light; focused the tele-

The oil-dropexperiment.

Filtered air, intowhich an atomizer

(A) blows oildroplets, is

admitted intochamber (C).

Droplets of oil findtheir way through

pinhole (p) into anair condenser

bounded by plates(M) and (N) heldapart by ebonite

posts (a); the platesare charged by the

battery (B),controlled by switch

(S). The oil dropsare illuminated and

seen through thewindow (c). (From

Millikan's TheElectron published

in 1917.)

I. ISOLATION OF INDIVIDUAL IONS AND MEASUREMENTOF THEIR RELATIVE CHARGES

In order to compare the charges on different ions, theprocedure adopted was to blow with an ordinary com-mercial atomizer an oil spray into the chamber C (Fig. 3),

Fie. 3

The air with which this spray was blown was first ren-dered dust-free by passage through a tube containinggl?-<; wool. The minute droplets of oil con=tit-t-ing the

* -tt. ' ' Hem h"-"'nij 'Hiif ' * i

scope; sprayed oil over the top of theplate; then came back to look throughthe telescope. I saw a most beautifulsight. The field was full of little star-lets, having all colors of the rainbow.The larger drops soon fell to the bot-tom, but the smaller ones seemed tohang in the air for nearly a minute.They executed the most fascinatingdance. I had never seen Brownianmovement before. Here was a spectac-

ular view of it. The tiny droplets werebeing pushed first that way and thenthis way by the actual molecules in theair surrounding them. I could hardlywait until I could try an electrical fieldupon them to see if they were charged.I knew there were two or three banks ofsmall storage cells in the laboratory. Alarge number of these had been con-nected in series and mounted in com-partments on a small truck. Each one

hoped to hold the cloud steady so that hecould study its rate of evaporation. To do this,he increased the strength of the electric field,which actually had the effect of dispersing theparticles by acting differently on differentlycharged particles. Millikan wrote, "the disper-sal seemed at first to spoil my experiment. Butwhen I repeated the test, I saw at once that Ihad something before me of much moreimportance than the top surface.... For re-peated tests showed that whenever a cloudwas thus dispersed by my powerful field, a fewindividual droplets remained in view." Whenhe saw that by turning off the field, drops fell atdifferent rates, he realized that their differentweights had been balanced by their differentcharges or numbers of ions. Timing the des-cent of a droplet whose weight he could findby means of Stokes's law, he discovered themagnitude of its charge needed to balance itsweight. Comparing droplets falling at differentrates, he was able to eliminate most of theeffect of evaporation. The results he obtainedalways came out, within the limits of hismeasurements, to 1, 2, 3, 4, or some otherexact multiple of the smallest charge on adroplet he obtained. "Here then [from thisbalanced-droplet method] was the first defi-

nite, sharp, unambiguous proof that electricitywas definitely unitary in structure." He ob-tained a value of e as 4.65x 10"10 electrosta-tic units.

On 31 August 1909 Millikan presented hisresults at a meeting in Winnepeg, Canada, ofthe British Association for the Advancement ofScience. Delivering his paper, he had thegood fortune to be able to contradict a state-ment that Lord Rutherford had made a fewdays earlier: "It has not yet been possible todetect a single electron by its electrical oroptical effect and thus count the numberdirectly, as in the case of alpha particles."

Soon after Millikan's return from Winnepeg,Fletcher came to him asking for help inchoosing a thesis topic. Millikan showed himthe apparatus that had been used for thebalanced-drop experiment (which Fletcher de-scribes in the early part of this excerpt) andsuggested he work on using less quicklyevaporating substances to find more accuratevalues of e. While the general features ofMillikan's experiments had by this time—earlyfall 1909—been set, they did undergo a "pro-cess of significant maturation" according to

Holton, while Fletcher worked with Millikan.Until then, values of different "balanced"water drops were compared. In the newprocedure using oil drops, sets of data wereobtained on the risings and fallings of a singleoil drop. Droplets, often charged by friction,were introduced into an electric field betweentwo charged plates. The charges on thedroplets were changed by irradiating them.The speeds of descent of a single droplet withdifferent charges were compared and foundall to yield multiples of a smallest value, thatvalue being e. Millikan had to make adjust-ments for the viscosity of the air (or othermedium used) in using Stokes's law, becausethe particles observed were so minute that themedium could no longer be treated as entirelycontinuous. (When larger particles were ob-served, their behavior did conform to the law,but the advantage of having long times ofdescent—sometimes over a minute—was lostbecause the heavier particles fell much morequickly.)

Millikan and Fletcher continued the work foryears, with many variations, and finally ob-tained a value of e at 4.774 ( ± 0.005) x 10"1 0

electrostatic units. —DG

PHYSICS TODAY / JUNE 1982 45

Millikan (photo below, in the center) in 1908 flanked by A. A. Michelson (at left), Henry G. Gale(right) and Carl Kinsley (front). (Photograph by Crowe, courtesy AIP Niels Bohr Library.)Fletcher in 1936 with Millikan (to his left) and Leopold Stokowski, with whom he worked on re-cording equipment. (Photograph provided by Stephen Fletcher.)

of these units would produce 1000 voltsdc at its terminals. I soon rolled one ofthem into place near my crude appara-tus. Insulated wires were attachedthrough a switch to the two terminalsof the 1000-volt dc battery. I finishedmost of this that first afternoon. Thenext morning I spent some time adjust-ing it and installing a meter to read thevoltages applied to the plates. I wasthen ready to try the battery on thesetiny oil drops.

Once more the atomizer was used tospray some of the oil across the topplate. As I looked through the tele-scope I could see the tiny stream of oildroplets coming through the hole.Again I saw beautiful stars in constantagitation. As soon as I turned on theswitch some of them went slowly upand some went faster down. I wasabout to scream as I knew then thatsome were charged negatively and oth-ers positively. By switching the fieldoff and on with the right timing onecould keep a selected droplet in thefield of view for a long time. I wentimmediately to find Millikan, but couldnot find him so I spent the rest of theday playing with these oil droplets andgot a fairly reasonable value of e beforethe day ended. The next day I foundhim. He was very much surprised tolearn that I had a setup that wasworking. He came down to the labora-tory and looked through the telescopeand saw the same beautiful sight of thestarlets jumping around that I hadalready seen and have described above.He was very much excited, especiallyafter turning on the field. After watch-ing for some time he was sure we couldget an accurate value of e by thismethod. He stopped working with Be-geman and started to work with me.We were together nearly every after-noon for the next two years. He calledthe mechanic who worked in our phy-sics shop and we outlined a new designfor our apparatus and asked him to

build it. The principal changes were tomake the plates more accurate and toenclose the air between the plates toprevent air drafts. Also, we obtained aradium source or x-ray source that wecould shoot at the chamber to produce agreater ionization. The actual design isdescribed in the first paper publishedabout this work. I want to say moreabout this first paper later.

Making the principal changes tookabout a week. Afterwards we startedin earnest on this research work, whichwas later to become so famous. Afterworking five or six weeks we had thepress come into our laboratory and seeand hear our results. We also made apopular presentation. The papers werefull of this wonderful discovery. It wasthe first real publicity that I had everreceived. My name ran right alongwith Professor Millikan's in the news-papers. I spent considerable timeshowing these experiments to variousVIPs from all over the country.

I remember one of them was thegreat Charles Steinmetz from the Gen-eral Electric Company. He was onewho did not believe in electrons. Hecould explain all the electrical phenom-ena in terms of a strain in the Ether.After watching these little oil dropletsmost of one afternoon, he came andshook my hand and said, shaking hishead, "I never would have believed it. Inever would have believed it" and thenleft.

This was all great publicity, but Ibegan to wonder if this work was to bemy thesis as Millikan had promised atthat first conference in December 1909.However, during the spring of 1910 westarted together writing a paper to bepublished about the new research.

I wrote more of it than he did, par-ticularly about the modification ofStokes's law and the arrangements ofthe data. He went over it all andchanged the phrasing somewhat tomake it read better. All the time I

thought we were to be joint authors.Before going further let me quote

some from that paper. If you want toread the whole paper, it is available inthe library.

"The Isolation of an Ion, aPrecision Measurement of Its Chargeand the Correction of Stokes's Law."

Science, 30 September 1910. . . Mr. Harvey Fletcher and my-self, who have worked together onthese experiments since December1909 have studied in this waybetween December and May fromone to two hundred drops whichhad initial charges from 1 to 150and made from oil, mercury andglycerine and found in every casethe original charge on the drop tobe an exact multiple of the small-est charge which we found that thedrop caught from the air.

Throughout the paper such statementsas this occur:

Mr. Fletcher and my own meantimes on a given drop generallydiffer from each other by less thanVioo second.Phyllis was born 21 May 1910, and as

you will see, that is about the time wefinished this first paper. When she wasabout one month old, I was babysittingwith her as Lorena had gone out some-where with some of her friends. An-swering a knock, I went to the door andwas surprised to see Millikan. I won-dered why he had come to our humbleapartment. I soon found it was todecide who was to be the author of thepaper referred to above. There werefour other papers in the formativestage that were coming out of these oil-drop experiments and I had expectedthey would all be joint papers.

He said that if I used a publishedpaper for my doctor's thesis that I mustbe its sole author. The five papers onwhich we did the experimental worktogether were• "The Isolation of an Ion, a Precision

PHYSICS TODAY / JUNE 1982

Measurement of Its Charge, and theCorrection of Stokes's Law." Science,30 September 1910—Millikan• "Causes of Apparent Discrepanciesand Recent Work on the ElementaryElectrical Charge." Phys. Z., January1911—Millikan and Fletcher• "Some Contributions to the Theoryof Brownian Movements, with Experi-mental Applications." Phys. Z., Jan-uary 1911—Fletcher• "The Question of Valency in Ga-seous Ionization." Phil. Mag., June1911—Millikan and Fletcher.• "A Verification of the Theory ofBrownian Movements and a Direct De-termination of the Value of Ne forGaseous Ionization." Phys. Rev., Au-gust 1911, and Le Radium, 1 July1911—Fletcher.

It was obvious that he wanted to bethe sole author on the first paper. I didnot like this, but I could see no otherway out, so I agreed to use the fifthpaper listed above as my thesis.

As you will note from the above, Iwas also sole author on the third andjoint author with Millikan on the sec-ond and fourth.

Thus the authorship of these paperswas settled in our humble apartmentabout one month after Phyllis wasborn.

People have frequently asked me if Ihad bad feelings toward Millikan fornot letting me be a joint author withhim on this first paper, which really ledto his getting the Nobel Prize. Myanswer has always been no. It is ob-vious that I was disappointed as I haddone considerable work on it, and hadexpected to be a joint author. ButMillikan was very good to me while Iwas at Chicago. It was through hisinfluence that I got into the graduateschool. He also found remunerativejobs for me to defray all my personaland school expenses for the last twoyears. Above this was the friendshipcreated by working intimately togetherfor more than two years. This lastedthroughout our lifetime. When hewrote his memoirs shortly before hedied he had probably forgotten some ofthese early experiences.

I graduated with a PhD in physics in1911 summa cum laude. This was thefirst such high honor that was given toa physics student at the University ofChicago. At this graduation I was alsoelected an honorary member of PhiBeta Kappa. I received very warmpraise from my classmates.

It was from these classmates that therumors arose that I had been unfairlytreated by Professor Millikan, andthese rumors persisted at the RyersonPhysical Laboratories for many yearsafter I left there. This is one of thereasons that I have outlined in somedetail my connection and contributionto the famous oil drop experiment. D

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