Influences on Einstein's Early Work in Relativity Theory : a Report Based on Archival Materials

O R G A N O N 3(1966) _{AUTEURS ET PROBLÈMES}

Gerald Holton (United States)

INFLUENCES ON EINSTEIN’S EARLY WORK IN RELATIVITY THEORY

A R E P O R T B A S E D O N A R C H IV A L M A T E R IA L S *

1. INTRODUCTION

On M arch 11, 1952, A lbert Einstein w rote to C arl Seeling: “Betw een the conception of th e idea of this special re la tiv ity theory and th e com­ pletion of the corresponding publication, th ere elapsed five or six weeks. B ut (he adds ra th e r cryptically) it would be h ard ly correct to consider this as a b irth date, because earlier th e argum ents and building blocks w ere being prepared over a period of years, although w ithout bringing about the fundam ental decision” J.

Can w e get some idea of w hat m ay have happened d u ring those years and w hat — or who — helped to bring about th e “fundam ental decision”?

I have been in terested in studying th e various influences th a t w or­ ked th e ir w ay into E instein’s early publications on relativity, and con­ versely, the reception accorded to these publications and ideas. How large or how sm all was the effect of the w ork of earlier physicists? Is there some strong influence th a t has so fa r been overlooked? In w h at respects was E instein’s view of the problem differen t from th a t of his contem poraries — for exam ple, in th e role th a t experim ent resu lts played com pared w ith epistemological considerations? And how do such differences explain th e ra th e r hostile early response of th e scientific com m unity to his work?

* Paper presented at the Sym posium on A lbert E instein at the X lth Interna­ tional Congress of the H istory of Science, W arsaw, August 25, 1965.

1 The literary rights to quotations from th e w ritin gs o f Albert E instein belong to the Estate of A lbert Einstein; perm ission to use quotations should be secured from th e Executor, Dr. Otto Nathan, 55 East Loth Street, N ew York City.

The style of E instein’s first 1905 paper on rela tiv ity was m arkedly different from w hat was th e accepted as cu rren t practice, different, for example, from L orentz’s or even Emil Cohn’s (whose theory of electro­ dynam ics of moving bodies was taken q u ite seriously a t th e time, e.g. by B ucherer and Abraham). Nor are th ere really sufficient clues in th e lite ra tu re w hich biographers cite th a t help us to u nderstand the s tru ­ ctu re of th a t paper. You m ay recall it starts w ith th e question w hy th ere should be differen t equations for dealing w ith th e emf generated in a moving conductor going past a statio n ary m agnet as against a sta­ tio nary conductor near a moving m agnet. Then, w ithout specifically m entioning by nam e an y of th e now-so-fam ous experim ents, it goes on to dismiss the conception of absolute motion and of th e ether, and attacks the discussion of relativistic kinem atics through a fundam ental philosophical exam ination of th e concepts of space and time. Only later on comes J h e trea tm e n t of M axw ell’s equations and finally, alm ost as an afterthought, some predictions about electron motion, giving the equations „according to which th e electron m ust move in conform ity w ith the theory presented h e re ”. Only E instein’s friend, co-worker at the P a te n t Office, and form er fellow -student, nam ely M ichele Besso, is cre­ dited d irectly by Einstein in this paper w ith being helpful.

This is a strange and unique w ay of going about electrodynam ics in 1905. M ax von Laue, one of th e first and forem ost partisans for and contributors to relativ ity theory, nevertheless confessed to M argot Ein­ stein in a le tte r of October 23, 1959, th a t he had feld fundam ental diffi­ culties for a long time. He w rote th a t afte r the publication of E instein’s paper in 1905 ging m ir langsam aber stetig eine neue W elt auf. Ich habe

viel Mühe darauf verw enden müssen... . Und ganz besonders waren es erkenntnistheoretische Schw ierigkeiten, die m it zu schaffen machten. Aber seit etw a 1950 glaube ich, diese überw unden zu haben... . Profes­

sor Infeld, in his book on A lb ert Einstein (1950), sim ilarly w rites (p. 23): “The title sounds modest, y et as we read it we notice almost im m edia­ tely th a t it is different from other papers. There are no references; no authorities are quoted, and the few footnotes are of an explanatory character. The style is simple, and a great p art of this article can be followed w ithout advanced technical knowledge. B ut its full u nd erstan ­ ding requires a m a tu rity of m ind and taste th a t is m ore ra re and p re­ cious than pedantic knowledge, for E instein’s paper deals w ith the most basic problems; it analyzes the m eaning of concepts th a t m ight seem too simple to be scrutinized...” .

So in retro spect it is not en tirely surprising th a t it took also a long brooding period for Einstein him self before this rem arkable egg was hatched. B ut w here, when, and from whom m ight Einstein have obtai­ ned some of his point of view, his questions, and his method?

In flu e n c e s on E in ste in ’s E a rly W o rk 2 2 7

2. ARCHIVAL HOLDINGS

One w ay to begin to find out is, of course, to look a t docum ents. Therefore, after these questions had raised them selves, I began to search for w hatever docum ents m ight have survived th a t would be relevant. In th e possession of A lbert E instein’s Estate, and k ep t for th e tim e being at the In stitu te for Advanced S tudy at Princeton, th ere are in ­ deed docum ents — about tw en ty m etal file-draw ers full, counting only the most scientific p a rt of Einstein’s m anuscripts and th e largely u n ­ published correspondence.

E instein’s rem arkable and devoted secretary, Miss H elen Dukas, has been putting the docum ents into system atic order; over th e p ast th ree years, under m y general supervision, the m aterial has been catalogued w ith the help of some g raduate stu d en t’s labor and by m eans of m y periodic visits from H arvard, plus some w ork I p u t in d u ring a sabba­ tical leave w hich I spent a t th e In stitu te for A dvanced S tudy a t P rin ­ ceton a year ago. Copies of correspondence are continually being re ­ ceived and added, b u t a prelim inary archival calendar is now fairly well finished, and it has begun to be p u t to use in scholarly work. In this paper itself I shall be draw ing on a num ber of h ith erto u n ­ published documents, and thereb y can hope to fu rn ish one exam ple of th e m any problem s th a t can now be attacked w ith the aid of th e archives.

L etters — originals or copies, often to and from the correspondent, on scientific m atters and other professional in terests — are available under the following nam es (to cite only a few of those correspondents who are included in th e archives and who are now deceased): Bohr, Besso, Bucherer, Cassirer, Eddington, Ehrenfest, Jam es Franck, Gross- mann, H adam ard, H ilbert, Langevin, v. Laue, Lenard, Levi-Civita, Lo- rentz, D. C. M iller, Mach, Meyerson, N ernst, Pauli, Planck, Reichenbach, Schrödinger, de Sitter, Sommerfeld, Schlick, Swann, S tark, Szilard, Weyl, Wien. All this is quite ap art from an im m ense correspondence on social, political, and other m atters; personal correspondence w ith kings and commoners, w ith such persons as F reu d and Thomas M ann, W eitzm ann and Russell, Shaw and N ehru, as w ell as job seekers and plain people in need of advice. Einstein w as app aren tly un tirin g ly generous in his response w henever th ere was any good, hum an cause or interesting idea.

In addition, th e re are eleven notebooks, startin g from E instein’s stu ­ dent days; a few trav el diaries; folders upon folders of published m a­ nuscripts, m any in early d raft; and several dozen unpublished m anu­ scripts.

All th is survived, m ore or less by good luck: On retu rn in g from a trip to th e U nited States in th e w inter of 1932-33, Einstein found on

reaching Europe th a t H itler had taken over in G erm any. Einstein never again set foot on G erm an soil, and most of the correspondence was brought out by diplom atic pouch.

One of th e first things I looked for was, of course, any m anuscript or d ra ft of E instein’s 1905 paper on R elativ ity Theory. B ut p articu larly for the early papers, Einstein destroyed or discarded th e m anuscripts w hen th ey w ere retu rn e d from the p rin ter, if they ever w ere. Einstein him self had occasion to re g re t this. For du ring a w ar-bond drive in the U nited States during W orld W ar II, he was asked to donate th e m anu­ script, and w hen he could not oblige in this way, h e was persuaded to w rite the paper out all over again in longhand. Miss Dukas recalls th a t she dictated it to him from his published paper, and th a t he kept in te r­ ru p tin g saying th a t th ere is a sim pler or m ore elegant w ay of expressing m atters. The tem ptation to w rite som ething different, however, was overcome, and th e m anuscript w as “auctioned” off to the person, who promised to b uy th e largest am ount of W ar Bonds (which tu rn ed out to be several m illion dollars), and who, in tu rn, deposited the m a­ nuscript in th e L ib rary of Congress in W ashington.2

Thus, th e re is no contem poraneous d ra ft or m anuscript from w hich one m ight learn som ething of the genesis of th e paper. B ut there are tw o notebooks w hich Einstein k ep t w hile still a student at the P oly­ technic In stitu te at Zürich (ETH) during th e period 1897 to 1900. Both are sets of lectures notes tak en in the physics course given by Heinrich F riedrich W eber whose special field of w ork was altern atin g -cu rren t technology. One of them is on heat and therm odynam ics, th e other on technical problem s such as liquefaction of gases (w ith detailed drawings), and electricity from Coulom b’s law to induction. B ut it does not even go to M axw ell’s w ork. A nd on this hangs p a rt of m y tale. For w hat was left out was exactly w hat young Einstein was w aiting for in his stu ­ dies. The fact th a t he was throw n on his own devices had, as we shall see, some interesting consequences in th e genesis of rela tiv ity theory.

3. READING AT HOME

As Besso w rote (in his notes of A ugust 1946 for Professor Stickel- b erg ’s article on Einstein in Sw itzerland), Einstein cam e to the A arau K anton-school in 1896 “w ith th e (then m uch-debated) questions con­ cerning the palpability (G reifbarkeit) of ether and of atom s” in mind. W hen he w ent on to th e ETH in Zürich, the lectures of physics m ade no great im pression on Einstein who found his teachers’ discussions “self-explanatory” . It w as indeed W eber who, Besso reports, said once

2 And so it is both true and false that “E instein ’s m anuscriptis now in the Library of Congress, W ashington” as the Bib liography of Scientific Papers of

In flu e n c e s o n E in ste in ’s E a rly W o rk 2 2 9

to Einstein, “You are a clever fellow! B ut you have one fault: One can’t tell you anything, one can’t tell you an y th in g ”. C learly W eber could not.3

This circum stance is corroborated by E instein’s classm ate, Louis Kollros (in C arl Seeling, editor, Helle Z eit-D un kle Z eit, Zürich, 1956): “There w as not v ery m uch theoretical physics done a t th e Poly, w hich was strong in m athem atics... (W eber’s) lectures concerning classical physics w ere lively; but we w aited in vain for an exposition of M ax­ w ell’s theory. We knew th a t the theory was founded on th e id en tity of th e transm ission of electricity and light, and th a t the w ork of H ertz con­ cerning electric waves had verified th e theory. We w ould have gladly learned m ore about it. Above all, it was Einstein who was disappointed (for, as Einstein recalls in his Autobiographical Notes, it w as «the most fascinating subject at the time»). In order to fill this gap, he undertook to study on his own the w orks of Helm holtz, M axwell, H ertz, Boltz­ m ann and L orentz”.

K ollros’s list of authors rem inds us of th e fam ous passage in Ein­ stein ’s Autobiographical Notes which does seem v ery relev an t to th e question of early influences shaping th e thought expressed in th e 1905 relativ ity paper. The passage (page 15) concerns the period of 1897-1900: “I entered th e Polytechnic In stitu te of Zürich as a stu d en t of m ath e­ m atics and physics. There I had excellent teachers (for exam ple, H urwitz, Minkowski), so th a t I really could have gotten a sound m ath e­ m atical education. However, I w orked m ost of th e tim e in th e physical laboratory, fascinated by the direct contact w ith experience. The balance of the tim e I used in the m ain in order to stu dy at hom e th e w orks of Kirchoff, Helmholtz, Hertz, etc.”

The really interesting p a rt m ay w ell be th e stu dy of th e last, the

e t c . Who is hiding behind th e phrase et cetera? P erh ap s somebody who

p repared the w ay Einstein w ent in presenting his rela tiv ity theory. We m ust, of course, not dismiss Kirchhoff, Helmholtz, and H ertz, or for th a t m atter Boltzmann, Mach, Poincare, and Lorentz. B ut someone else is also needed to explain E instein’s 1905 paper. If this n eutrino exists, we should be able to find it. As you w ill see, we have now a good can­ didate for this honor.

4. MAXWELL, DIRECT AND INDIRECT

F irst a look at the others. From about 1903 on, Einstein was a t th e P ate n t Office in Berne for about six years. According to a m anuscript note from Besso in the Archives, the vacancy was s p e c i f i c a l l y a d v e r t i s e d as requiring an “intim ate acquaintance w ith M axw ell’s

3 W eber’s successor, however, w as Pierre W eiss, w ho brought Einstein back to Zurich from Prague in 1912.

th eo ry .” Einstein qualified on this score by the spring of 1905 — of th a t th ere is no doubt — and he m ust have know n M axw ell’s theory earlier. There are a num ber of corroborating statem ents (other th an K ollros’s and Besso’s), for exam ple in a le tter to von Laue, sent by Einstein from

P rinceton on 17 J a n u a ry 1952:

“D ear Laue: I now have received your book concerning special rela­ tiv ity th eo ry and find th a t it is v ery good... (But) w hen one looks over your collection of proofs of the special rela tiv ity theory, one becomes of the opinion th a t M axw ell’s th eo ry is unquestionable. B ut in 1905 I already knew certainly th a t M axw ell’s theory leads to false flu ctu ­ ations of radiation pressure and, w ith it, an incorrect Brow nian motion of a m irro r in a Planckian radiation cavity. In m y view, one could not get arround ascribing to radiation an objective atom istic stru ctu re which, of course, does not fit into th e fram e of M axw ell’s theory... U nfortunately, th e fifty years w hich have since passed have not brought us closer to an understanding of atom istic stru ctu re of rad iatio n ” .

G ranting th a t Einstein obviously knew M axw ell’s theory by 1905, the question is left through which books he learned it. I t m ay have been by direct stu d y of M axw ell’s work, although th ere is no docum entary evidence for this. At any rate, d irect study would not have been the only or even th e most im portant way.

M axwell came to most G erm an students of physics first through the w orks of Helmholtz, Boltzmann, and H ertz. They are in m any ways quite different, b u t they also have a t least one elem ent in common: th a t these presentations of M axw ell’s th eo ry are q u ite un-M axw ellian, that, in differen t degrees, their style is even fu rth e r from th a t of M axwell th a n from E instein’s paper. On this point, a brief word m ust suffice here. For exam ple, to a contem poraneous physicist in England and France, H elm holtz’s w ay of thinking m ust have looked quite terrifying. F ully half of this introductory volum e of the Lectures on Theoretical

Physics is spent on th e following topics: philosophy and science; physical

science; critique of th e old logic; concepts and th e ir connotations; hypo­ theses as bases for th e laws; the com pleteness of scientific experience and its practical significance; and so forth. M axw ell’s work proper is presented in Volume 5 of th e Lectures on Theoretical Physics, issued in 1897. The term inology th e re is one Einstein used to some ex ten t later. W hat catches our eye is th a t th ere is v ery little attention to experim entation. One cannot, for exam ple, find a reference to the Michelson experim ents which, afte r all, w ere first tried under the sym pathetic eye of H eim holtz him self. Even th e section entitled “The Necessary P rop erties of th e E th er” has no reference to experim ents. And in the only paper which Helm holtz w rote specifically on the subject of M axw ell’s theory, called Consequences of M axw ell’s Theory

In flu e n c e s on E in ste in ’s E arly W ork 2 3 1

of actual experim ents. W hat Einstein m ight have obtained from studying H elm holtz’s version of M axw ell’s theo ry is first of all a re ­ inforcem ent of a taste for a consciously epistemological approach, and a confirm ation th a t in this area ex perim ents do not count crucially.

Reading H ertz, whose collected w orks w ere available b y 1895 E instein w ill have seen H ertz’s first thorough essay on The F unda­

m ental Equations of M axw ell’s Electrodynam ics published in 1884,

and th e article significantly entitled Concerning th e Fundam ental

Equations of Electrodynam ics for M oving Bodies of 1890. Even th is

greatest of experim enters in the field of electrom agnetism m akes no m ention of th e “eth e r” experim ents th a t have recen tly loomed so large in some discussions of the origins of re la tiv ity theory. On th e other hand, the m ain effect th e stu d y of H ertz’s w ork m ight have had upon a reader like Einstein is perhaps best characterized by H ertz’s ow n rem ark in th e Principles of M echanics: “In general, I owe v ery m uch to th e fine book concerning the developm ent of m echanics by M ach.” It w as one of v ery m any forces urging young Einstein tow ard E rn st Mach. As h e said la ter in his Autobiographical Notes, M ach’s

H istory of Mechanics “shook this dogmatic fa ith ” in “mechanics as

the final basis of all physical thinking... This book exercised a p ro ­ found influence upon me in th is reg ard w hile I was a student... M ach’s epistemological position... influenced m e v ery greatly...” 4

5. MACH

Indeed, it is an ironic circum stance th a t th e state of contem porary research physics during th e period w hen th e young Einstein began to w ork on special relativ ity w as really characterized by such a de­ gree of dogmatic rig id ity as th e thought. As S tephen B rush has re­ cen tly pointed out,5 the m echanistic view of physical re a lity w as th en defended by only a “few lonely m en such as Boltzmann... The m ost «advanced» and «sophisticated» theories w ere those th a t took a p u rely phenomenological viewpoint: scientific theories should deal only w ith the relations of observable quantities, and should strive for economy

4 Besso, w ritin g in late 1947 to Einstein, rem inds him that during the year of 1897 or 1898, Besso had drawn E instein ’s attention to Mach, and he asks w heth er it is correct “that this introduction (to Mach) fe ll in to a phase o f d evelopm ent of the young physicist w hen th e M achian style o f thin king pointed d ecisively at observables — perhaps even, indirectly, to «clocks and m eter sticks»”? The cor­ respondence of Einstein abounds w ith references to th e in fluence of Mach in the form ative years o f relativity theory. For exam ple, in a letter of A ugust 8, 1942 to A. S. N ash, Einstein wrote: “In the case of Mach, th e in fluence w as not only through his philosophy, but also through his critique concerning th e fu n d a ­ m ents of physics”.

of thought ra th e r th an try in g to explain phenom ena in term s of unobservable entities...” In short, around 1900 M ach’s views w ere no longer those of an isolated fighter, the role w hich he ra th e r liked and, w hich he appeared to have in th e books th a t young Einstein read w ith deep-felt agreem ent. On the contrary, it w as the great H,. A. Lorentz and H. Poincare whose styles w ere coming to be out of step w ith the new physics exem plified b y the Curies, Rutherford, Einstein himself, and a t least a t one point, even by P lanck.6

Som ething of this flavour comes through in letters in Einstein’s correspondence, and a famous passage in E instein’s Autobiographical

N otes is closely related:

“Reflections of this typ e m ade it clear to me as long ago as shortly after 1900, i.e. sho rtly after P lan ck ’s trail-blazing work, th a t neither m echanics nor therm odynam ics could (except in lim iting cases) claim exact validity. By and by I despaired of th e possibility (Nach und

nach verzw eifelte ich an der M öglichkeit) of discovering th e tru e laws

by means of constructive efforts based on know n facts. The longer and the m ore despairingly I tried (Je länger und verzw eifelter ich

m ich bem ühte), the more I came to the conviction th a t only th e dis­

covery of a universal form al principle could lead us to assured resu lts” .

No m a tter how some of th e younger physicists of th e tim e w rest­ led w ith the problem s of physics, th e use of conceptions developed in nineteen th -century physics seemed to them m erely to produce failu re and despair. It is not too much to say th a t th e new physics they fashioned was first of all eine P hysik der V erzw eiflung. And

6 Thus in an unpublished letter from Berlin (1931) from Max Planck to R. W. Wood, kindly made available by Professor Wood’s son to the American In stitu te of Physics Project on th e H istory of Physics, and on deposit at their A rchives in N ew York: “Dear Colleague: You expressed recently, at our nice dinner at Trinity H all, th e w ish that I should describe to you more concerning the psychological side of the considerations w hich led m e at the tim e to postulate the hypothesis of energy quanta. H ere I w ant to accom odate your w ish. B riefly put, I can describe th e w hole effort as an act of desperation, for by nature, I am peaceful and against dubious adventures. B ut I had been figh tin g already for six years, from 1894 on, w ith the problem of equilibrium betw een radiation and m atter w ithout having any success; I knew that this problem is o f fundam ental significance for physics; I knew th e form ula w hich provides the energy distribu­ tion in the norm al spectrum ; a theoretical explanation, therefore, had to be found at all cost, w hatever the price. C lassical physics w as not su fficient, that w as clear to me... (Except for th e tw o law s of therm odynam ics) I w as ready for any sacrifice of m y established physical convictions. N ow Boltzm ann had explained that therm odynam ic equilibrium com es about through statistical equilibrium , and w hen one applies th ese considerations to the equilibrium b etw enn m atter and radiation, one finds that one can prevent the deterioration of energy in radiation by m eans of the supposition that energy is from the beginning forced to remain in certain quanta. This w as a purely form al assumption, and I did not really think m uch about it excep t just this: No m atter w hat the circum stances, may it cost w hat it w ill I had to bring about a p ositive resu lt”. (Translation by G. H.).

In flu e n c e s on Eirbstein’s E a rly W o rk 2 3 3

here th e role of Mach as iconoclast and critic of classical conceptions was p articu larly im portant; for w h eth er or not E instein’s assessm ent of th e contem porary scene was right, it is certain th a t M ach’s critical force and courage m ade a strong im pression on him, as on so m any others.

We cannot go h ere into the vast and im p ortan t topic of th e rela­ tion betw een Einstein and Mach. Suffice it to say th a t th e archives help to illum inate each of th e five stages in th e dram a: (1) M ach’s place in physics and philosophy of science in th e early years of this century; (2) E instein’s early acceptance of the m ain features of M ach’s doctrine; th e Einstein-M ach correspondence and m eeting; (3) the re ­ velation in 1921 of M ach’s sudden and b ru tal attack on E instein’s re la tiv ity theory (occasioned, it appears to me, in good p a rt by the fact th a t Mach discovered th e anti-M achist kern el of E in stein ’s episte- mology even before Einstein did him self); and (4) E instein’s own fu rth e r developm ent of a philosophy of know ledge in w hich he rejects m any b u t not all, of his earlier M achist tendencies. Thus at th e end of th is developm ent E instein w rites (on J a n u a ry 24, 1938, to C. L an- czos): Vom skeptischen Em pirism us etw a Mach’scher A r t herkom m end

hat das G ravitationsproblem m ich zu einem gläubigen Rationalisten gemacht, d.h. zu einem, der die einzige zuverlässige Quelle der W ahr­ h eit in der m athem atischen E infachkeit sucht.

In his letters, as in his Autobiographical Notes, Einstein later con­ tinued to acknowledge th e general bu t strong influence th a t Mach h ad been,. N evertheless, we can w ell und erstan d th a t a t h e a rt M ach’s rejection w as v e ry painful, th e m ore so as it w as somehow E instein’s trag ic fate to have th e contribution he most cared about be rejected by th e v ery m en whose approval and understanding Einstein w ould h ave m ost gladly had — a situation not unknow n in th e h isto ry of science. In addition to Mach, th e list includes these four: P o i n c a r e (who to his death in 1912, only once deigned to m ention E instein’s nam e in print, and then only to register his dissent); L o r e n t z (who gave Einstein personally every possible encouragem ent — short of fu l­ ly accepting this th eo ry of relativ ity for him self); P l a n c k (whose support of the special th eo ry of re la tiv ity w as u nstin tin g bu t who resisted E instein’s ideas on general relativity , not to speak of th e quantum theory of radiation); and M i c h e l s o n , who to th e end of h is days did not believe in rela tiv ity theory, and even once said to Einstein th a t he w as sorry th a t his own w ork m ay have helped to sta rt this “m onster” 7.

6. POINCARE AND LORENTZ

The influence on and response to E instein’s w ork on th e p a rt of both Poincare and Lorentz has also been a fascinating problem for th e historians of recen t science. A lthough the old m y th s w ill not die quic­ kly, th e y have been p re tty w ell exploded.8

To p u t it briefly, and w ithout intending in th e slightest to denigrate P oincare’s enorm ous accomplishments, we m ay say th a t h e saw the “crisis” in physics as one p rim arily revolving about experim ental dif­ ficulties, and th erefo re involving neith er epistemological nor funda­ m entally differen t theoretical reorientation. This is, of course, directly antith etical to E instein’s view of the m a tter a t about th e same time: The new e x p e r i m e n t a l findings, such as M ichelson-M orley ex­ perim ent, n eith er provoked th e crisis as Einstein saw it, nor w ere guides to th e new orientation needed. T hat Einstein’s w ork in 1905 is independent of P oincare’s investigations on electrom agnetism in 1904— 05 has now been rep eatedly and adequately established.

W hen it comes to th e debt of independence of Einstein w ith respect to L orentz’s work, and th e response of Lorentz to E instein’s early papers, the record is also quite clear. Einstein and others repeatedly said th a t he did not know of L orentz’s 1904 paper on electrom agnetic phenom ena.9 On this w ell-w orked ground, perhaps one need only to point out anecdotally how difficult it would have been for an almost unknow n P a te n t Office employee in a Swiss tow n such as B ern to have had direct access to th e Proceedings of the A m sterdam Academ y in w hich Lorentz published th e 1904 paper. In the R ijksarchiv at th e Hague, Holland, I found a le tte r from M. Laue, w riting to Lorentz on Novem ber 30, 1905, from Berlin, ap paren tly for th e first time, and in h is capacity as A ssistant a t th e In stitu te for Theoretical Physics (there­ fore, as P lanck’s assistant):

“Since th e Proceedings of the A m sterdam A cadem y are here more difficult to obtain th an other journals — th ey exist only in the Royal Bibliothek, and it lends out recent jo u rn als only for a day — I take th e lib erty of expressing to you the request to send me, if possible, a re p rin t of your publication, «Electrom agnetic Phenom ena in a System Moving w ith A ny V elocity Less th an th a t of Light»”.10

8 e.g. G. H o l t o n : On the Origins of the Special Theory of R e lativity . “Am. J. P h y s”. 28, 1960, p. 627; and G. H o l t o n : On th e Them ati c A n aly sis of Science:

The Case of Poincare and R e la tiv ity , in Melanges A lexan dre K o y r i . I, 1964,

p. 257.

9 For the evidences, see for exam ple H o l t o n : op. cit. In h is lectures and publications Lorentz repeatedly gave generous credit to the n ovelty and in de­ pendence of E instein ’s work. See also, for exam ple, Lorentz’s rem arks quoted in S i l b e r s t e i n ’s Theory of R e lativity , p. 117, and Lorentz’s footnote addendum on p. 10 of the 1912 edition of h is 1904 essay, in H. A. L o r e n t z , et al., Das

R e la tivitatsprin zip, Teubner.

10 The paper, originally printed as part o f the Proceedings of the A c a d em y

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If one had to sum m arize the difference betw een L orentz’s and E instein’s re la tiv ity physics in a sentence, one m ight say this: L o rentz’s wojrk can be seen som ew hat as th a t of a v alian t and ex tra o rd in ary captain rescuing a patched ship th a t is being b attered against th e rocks of experim ental fact, w hereas E instein’s is th e physics of despairing disenchantm ent w ith th e mode of tran sp o rtatio n itself — an escape to a ra th e r d ifferent vehicle altogether.

This brings us back for a final assault on th e problem of th e p roper antecedents of E instein’s w ork. N either th e shape nor the content of E instein’s 1905 paper, The Electrodynam ics of M oving Bodies, is ade­ q u ately explained as a sequel to th e chain L orentz-Poincare, or M ax- w ell-H elm holtz-Boltzm ann, or even K irchoff-M ach-H ertz. It is, of course, possible th a t E instein’s 1905 paper w as a creation w ith no direct p rep arato ry antecedent. And not having found an y models in th e w orks of th e m ajor contributors of the tim e, we m ay be tem pted to m ake this assum ption, even if reluctantly.

B ut it tu rn s out th a t w e do not have to do this. W orking w ith th e docum ents in the P rinceton Archives, I came across a clue th a t so far had not raised itself. And th is clue m ay lead u s to th e possibility of en tertainin g a quite differen t and unconventional view of th e direct ancestry of E instein’s thought processes leading to his 1905 paper.

7. A N ALMOST FORGOTTEN TEACHER

In one of th e thousands of letters th e re appears, only once and casually, th e nam e of a physicist who has not y et been m entioned here. I t is A ugust Foppl.

This nam e is know n to a num ber of older G erm an scientists and engineers, b u t to alm ost nobody else. It sounds v e ry much out of place com pared to “Kirchhoff, Helmholtz, H ertz, etc.” — so m uch so th a t it m ight w ell have ended up among the et ceteras m entioned in th e auto­ biographical note of Einstein. And indeed, th e search for the id en tity of A ugust Fopl starts v ery badly: Born in 1854, Fopl was, at th e age of 36 a technical high school teacher and ad m inistrator in Leipzig when h e published his first book, a ra th e r p edestrian little outline of elem entary physics. From the first exercise of th is L eitfaden (how ra ­ pidly m u st a disc spin to throw off a lightly adhering object?) to the last (explain parallel w inding in a.-c machines), th e re is nothing to in ­ dicate th a t th is m an could ever enter our story.

Two years later, now a civil engineer in Leipzig, Foppl published his first real book, Das Fachw erk im Raume. The book w orks up some D utch-language edition of the Proceedings, and later in th e E nglish-language edition. At that tim e, incidentally, Einstein probably k new no D utch and little, if any English. In a letter to Besso, dating no earlier than 1913, E instein w rites:

previous essays w hich Foppl has used for his degree candidacy at the U niversity of Leipzig in 1886, and, one supposes in connection w ith his subsequent task helping to design the M arkthalle of Leipzig. Yet, the book is by no m eans intended as a m ere practical m anual. On the contrary, Foppl objects to th e definition by w hich Fachwerk usually is regarded as a stru ctu re m ade of solid straig h t rods, to carry loads. “For me it is a p urely ideal stru c tu re ” (page 3). And in defense of this point h e plunges into an epistemological digression concerning the process and w a rra n t of introducing concepts such as rigid bodies, or ether, “which by no m eans in every respect coincide w ith th eir «realen

Urbildern»”.

And then, in 1892, Foppl was called to th e U niversity of Leipzig to teach, of all things, agricu ltu ral m achinery. As he later confessed cheerfully, he knew v ery little about this, so he spent th e sum m er touring factories to find out. His versatile intelligence seems to have helped him to absorb enough in a short tim e to enable him to teach th e course soon th ere after, b u t the subject was not w hat his m ind reached out for. And so, perhaps largely out of boredom, he began to w rite a treatise in his spare time, entitled M axw ell’s Theory of E lectri­

city, published in 1894. Indeed, this was the U r-ancestor of the book on

electricity by A braham -Foppl, la ter A braham -Becker, late B ecker- -S auter, etc., etc., — although a book v ery differen t from all these! And Foppl’s book was w idely bought, p articu larly because of the au th o r’s ability to p u t M axw ell’s theory clearly to engineers.

Perhaps as a resu lt of the book, Foppl was called in 1894 to the Technical U niversity at M unich — th e very city in which Einstein then was living, still a boy of 15 — and th ere Foppl stayed and w rote volubly, although as far as I could find out, h e never tau g h t from his book on M axw ell’s theory, th e book which, upon its publication, “aro­ used in the profession astonishm ent (A u fsehen ), for at th a t tim e the electrodynam ic considerations of the great English physicist, Maxwell, had h ard ly gained any ground” — to cite the introductory essay of the editors of th e F estschrift in Foppl’s honor on his 70th birthday, 25 J a n u a ry 1924.11

Before we look a t Foppl’s M axw ell, we can seize up the p articular style th a t characterized his thinking by considering Foppl’s immensely

11 Beiträge zu r Technischen Mechanik und Technischen P hysik, w ith essays by

som e o f Föppl’s students, including Theodor von Karman, Prandtl, H. Thoma, Tim oschenko, and Föppl’s tw o sons, L udw ig and Otto (Berlin, 1924). As this list alone shows, his influence w as large, although predom inantly in technical m e­ chanics. In 1904, Föppl m ade a gyroscopic experim ent to m easure the rate of rota­ tion of the earth, a work “w hich made him fam iliar w ith questions of absolute arid relative m otion”. And in 1914, he w rote an essay Über A b s o lu te und R e lative

Bewegung, a field “in w hich A. Föppl already, before Einstein, occupied him self

w ith the relativity theory, though not w ith such rem arkable su ccess” — according to the editors’ indroduction in the Festschrift.

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successful next w ork, the Vorlesungen ilber technische M echanik, pu ­ blished from 1898 on in several volumes. (The Festschrift, page vi, notes th a t to 1924 nearly 100,000 volum es of th is w ork w ere sold all over th e world.) Foppl him self sent seven editions through th e press, and others after him continued this work.

The Forew ord of Foppl’s M echanik, dated Ju n e 1898, tells us some­ thing ra th e r revealing about his special ta len t as a teacher and w riter. His students, he confesses, sometimes have com plained th a t he “pro­ ceeds too slowly ra th e r th an too fa st”, bu t he placed v ery special em ­ phasis on laying th e foundations carefully. I t is alm ost as if h e had a special eye for a read er w ho m ight not also have th e benefit of form al lectures on th e subject, and who m ight even have bad holes in this form al background.

A fter th e encouraging Foreword, the read er comes up against the firs t tw o sentences of th e text, typical in th e ir m ixture of straig h t forw ardness and discursiveness: “M echanics is a p a rt of physics. Its teaching rests, as does th a t of all n atu ra l sciences, in th e last analysis on experience”. And w ith this, he tu rn s to a discussion of th e m eaning of th e te rm “experience” (E rfahrung). By page 4, h e confesses “it is now, of course, no longer a question of mechanics, b u t a philosophical and epistemological question. Its discussion can, however, not be cir­ cum vented in an introduction to mechanics, no m a tter how, on the basis of earlier unfavorable experiences, one m ay shy aw ay from to u ­ ching on philosophical questions in th e exact sciences”. Foppl anno­ unces th a t his exposition of antim etaphysical and self-conscious em pi­ ricism is shared by leading scientists generally, and he specifically calls on th ree by nam e, in whose sp irit he believes he is proceeding: Kirchhoff, H einrich H ertz (once at M unich U niversity), and — E rnst Mach. Indeed, the volum e on dynam ics sta rts w ith th e section entitled

“R elative M otion”, and in the Preface Foppl says again: “One w ill

notice th a t th e (early p a rt of th e volume) is strongly influenced by th e w ork of Mach, w hich m ade a persistent im pression on m e”.

8. FOPPL’S m a x w e l l

We are beginning to see some evidences of th e kind of aproach to physics which would appeal to a young read er w ith th e kind of back­ ground, or lack of background, of Einstein in th e late 1890’s. This im pression is much reinforced w hen w e now re tu rn to F oppl’s In tro ­

duction into M axw ell’s Theory of E lectricity (Leipzig 1894). He w rites

in his Foreword th a t now not only th e professional physicist, th e te ­ acher, and the stu dent in physics, b u t also “th e scientifically train ed

electrotechnical e n g in e e r12 is attem pting to m ake him self acquainted w ith the foundations of this (M axw ell’s) theory in w hich today one m ay see w ith g reat probability th e perm anent foundation of every physical research in this domain... W ith this th ere is a recent dem and for an exposition of M axw ell’s theory w hich is as generally u n d erstan ­ dable as possible, b ut also scientifically correct”.

M axw ell’s original w ork, Foppl reports, is too difficult, and it h as m any m istakes or incom pletenesses w hich in th e m eantim e have been removed. Boltzmann, he says, has w ritte n such a w ork, b u t although nothing b etter of its kind can be done, Foppl sees need for another, different attem pt. W hat Foppl p articu larly w ants to provide is a “clear understanding of the concepts and considerations of this theory in order to give th e reader th e ability for his own, unsupervised w ork

(selbststaendigen Arbeiten) — in short, ju st th e kind of book an in ­

terested stu d en t would w an t if deprived of M axw ell’s theory in course lectures...”.

One idiosyncrasy of th e book th a t in terests us is explained in th e following m anner:

“In this book I h ave le ft out citation of sources as a m atter of principle... I w anted to w rite not a Handbook b ut a Lehrbuch which should as fa r as possible be cast in one piece. Therefore, I avoided as fa r as at all possible during th e w ritin g going back to publications which I had read earlier in order th a t I m ay not be d irectly influenced by them. I w anted to be led by th e developm ents and resu lts of other authors only insofar as these m atters had firm ly p en etrated into m y m em ory and had become an intim ate p a rt of m y own views. In th is m atter I hoped to attain a m ore unified and coherent exposition of th e whole system th a n w ould have been possible by going another w ay” .

As a consequence, th ere is a rem arkable paucity of references to actual experim ental situations, (of course, none is m ade to the M ichel- son or other eth er-d rift experim ents; b u t alm ost all references to any others are also missing).

In Foppl’s book w e find six m ain sections; th e first is on vector calculus, th e second on fundam ental electricity (Gauss’s Theorem, Cou­ lom b’s law, magnetism , induction, etc.), the th ird and fo u rth are th e usual extensions (ponderomotive forces, vector potential, energy rela­ tions in th e electrom agnetic field betw een statio n ary conductors). So far, it is all done com petently and patiently, b u t as if it w ere m erely prelude to som ething else.

Then we come to th e fifth m ain section, w hich tu rn s out to be of particular interest to us (pages 307—356). It is entitled The Electro­

12 It is, incidentally, w orth noting that Einstein cam e to the Zürich ETH in itially planning to study engineering, and that both E instein ’s father and closest uncle w ere in electrical engineering and manufacturing.

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dynam ics of M oving Conductors (Die E lektro dyna m ik bewegter Leiter),

and th e first chapter in it is entitled “Electrom otive Force Induced by M ovem ent”. The first paragraph in this first chapter is “R elative and A bsolute Motion in Space”, and starts in an unusual way:

“The discussion of kinem atics, nam ely of general th eo ry of motion, usually rest on the axiom th a t in the relationship of bodies to one another only relative motion is of im portance. There can be no ques­ tion of an absolute motion in space since th ere is absent any m eans to! find such a motion if th ere is no reference object a t han d from which th e motion can be observed and m easured... According to both M axw ell’s theory and the theory of optics, em pty space in actuality does not exist a t all. Even th e so-called vacuum is filled w ith a m edium , th e ether ... However, w ere we to accept the notion of com pletely em pty space, it w ould either be not at all subject to possible experience, or alternatively, we would first have to m ake a deep-going revision of th a t conception of space which has been im pressed upon hum an thinking in its long period of development. The decision of this que­ stion forms perhaps the most im portant problem of science of our tim e”.

Foppl continues a few lines later in this way:

“W hen in the following „we m ake use of th e laws of kinem atics for relative motion, w e m ust proceed w ith caution. We m ust not consider it as a p r i o r i settled th a t is, for exam ple, all the sam e w h eth er a m agnet (moves) in the vicinity of a resting electric circuit or w h eth er it is the la tte r th a t moves w hile the m agnet is at re s t” .

This, we recall, is precisely the w ay E instein’s paper sta rts — and Foppl adds a ra th e r fam iliar kind of G edanken-experim ent:

“To decide this question, we can consider a th ird case”. He proposes to th in k of both m agnet and conductor moving together, w ith no re ­ lative motion betw een them . Experience shows, h e says, th a t in this case the “absolute m otion” in itself causes no electric or m agnetic force in either body. This thought experim ent is then quickly develo­ ped to show th a t in the previous two cases w hat counts is only relativ e motion.

Later, Foppl goes on to discuss th e in teraction of moving m agnets and resting conductors (pp. 314—320), and resting m agnets and moving con­ ductors (pp. 321— 324). The rest of this section, too, m ay be directed first of all to engineers (unipolar induction, emf for a moving con­ ductor, m agnetom otive force, motion of a w ire loop in a m agnetic field,

etc.). There is a ra th e r brief last (sixth) part, a sum m ary of th e other

aspects of M axw ell’s work, including electrom agnetic w aves — again, w ith h ardly a reference to th e actual eth er experim ents. B ut our a t­ ten tio n is most attracted by th e fifth section of Foppl’s book; there, and in portions of the rest of the book, is th e kind of thinking w hich

would indeed have appealed to Einstein, and which in fact is far closer to th e stru ctu re and style of argum ent of E instein’s 1905 paper than the w ork of any of th e o th ers whom w e have nam ed — fa r more so than the books of Helmholtz, Boltzmann, Hertz, Runge for example.

9. OTHER REFERENCES TO FÖPPL

But before th e parallelism w ith Föppl carries the day, we m ust ask for m ore evidence. A fter all, earlier we dismissed th e suggestion th a t Einstein b uilt on P oincare’s and L orentz’s w ork of 1904, even though there are certain parallels.

We therefore m ust ask, w hy did not anyone else who knew Ein­ stein intim ately vouch in p rin t for the fact th a t Einstein read Föppl’s book. Thus I asked m y form er teacher and colleague, Einstein’s bio­ grapher, P hilipp F rank, w hy he had no m ention of Föppl in his book

Einstein: His L ife and Tim es (Alfred Knopf, New York, 1947). Profes­

sor F ran k replied he thought he had m entioned Föppl, and I showed him m y copy of th e biography in which it was plain th a t he had not. This was a considerable surprise to Professor Frank, b u t after some thought he referred me to th e G erm an edition of his book (Paul List Verlag, 1949, p. 38). In the Foreword, Professor F rank explained th a t this, the G erm an edition, is the first com plete edition of his m anuscript as w ritten in 1939— 1941. A nd there, on page 38, Professor F rank w rites th a t during his years as a student at th e Polytechnicum in Zü­ rich, “Einstein th rew him self into th e w ork of these classics of theore­ tical physics (of the late nineteen th century), th e lectures of Helmholtz, Kirchhoff, Boltzmann, th e electricity theo ry of J. C. M axwell and H. H ertz, and th e ir exposition in the textbook of A braham Föppl. Ein­ stein buried him self w ith a certain fanaticism day and night in these books from w hich he learned how one builds up th e m athem atical fram ew ork and th en w ith its help constructs th e edifice of physics” 13.

And there is one other guide th a t leads us to Föppl. T here are dozens of biographies of Einstein — most of them w ritte n at second or third hand. B ut h ere the A rchives at P rinceton delivered again a su r­ prise. I knew th a t a certain A nton Reiser had published a biography in English in 1930, w hen Einstein was still in Berlin. D espite a plea­ sant forew ord by Einstein, a t first glance it can h ard ly be considered reliable: for q u ite ap art from th e suspicious circum stance th a t no G er­ m an edition was ever brought out, th ere are also no credentials for the author of th e book. No other publications b y Reiser exist any­

13 Since Max A braham ’s version o f August Föppl’s book did not get done u n til 1904, it w ould be Föppl’s original work w hich m ust be m eant here; but th is slip does rem ind us that a substantial fraction of several successive gene­ rations of p hysicists w ere brought upon — and then taught from — Abraham - Föppl and later A braham -Becker.

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where, and a search in th e usual sources leads one to suspect th a t he sim ply does not exist. Now the m aterial in the A rchives shows th a t the nam e A nton Reiser was a pseudonym for Rudolph K ayser; and Rudolph K ayser was E instein’s own son-in-law who had proceeded w ith the biography w ith E instein’s acquiescence.

We re tu rn therefore to R eiser’s biography w ith new respect — and sure enough, th ere we find Foppl m entioned again as one of th e au ­ thors E instein read in his early days. So our m issing signal is r e ­ covered from the noise level of th e “et cetera”.

In balance we m ay say the role of Foppl was th a t he, w ith H elm ­ holtz on th e one hand, and Mach on the other, reinforced the unique aspects th a t made E instein’s 1905 paper so im p ortan t and, for his contem poraries, so difficult. As the various contem poraneous tre a t­ ments of elestrodynam ics showed, th ere was in principle a great diversity of possible roads open to Einstein. W hat Foppl was capable of providing in helping to shape E instein’s thought processes p rio r to the fashioning of th e relativ ity theory was, first of all, encouragem ent to go ahead in a m anner so very d ifferen t from th a t tau g h t to him at school and presented in all the m ost respectable books. It helps us to understand b etter w hat to this day rem ains as th e most startlin g part of E instein’s relativ ity paper: a m ixture th a t contains a good share of youthful philosophizing as a p a rt of doing physics; th e re ­ cognition th a t the fundam ental problem to be cracked is how to achieve a new point of view on the conceptions of tim e and space; the attention to G edanken-experim ents, and conversely, a quite low in ­ terest in the actual detailed experim ents which so m any of our tex ts m ake appear to be the point of d ep artu re of rela tiv ity theory. And th ere is also, I believe, some poignancy in th e discovery how Foppl may have reached across to Einstein — the book of an “outsider” who never had students in this subject to whom he could teach its contents in lectures, and the student who, also already being regarded by his teachers as an “outsider”, was looking to this book for the m aterial and stim ulation he could not get in th e ir lectures.

10. PRIORITY OF FUNDAM ENTAL THEORY

The Archives at P rinceton are fu ll of evidence of the gradual h a r­ dening of Einstein against the epistemological p rio rity of experim ent, not to speak of sensory experience. Again and again he p u t th e con­ sistency of a simple and convincing theory or a them atic conception higher in im portance th an th e latest new s from the laboratory — and again and again, he tu rn ed out to be rig h t.14 A theoretical and

episte-14 The sam e point of v iew is found, of course, also in E instein’s p u b l i s h e d w ritings. To give here only one early exam ple, in h is 1907 “Jahrbuch” ar­

mological w holeness of th e w ork is th e chief criterion in E instein’s mind. (The case is p articu la rly rich ly docum entable w ith respect to the aeth er-d rift experim ents). Again and again one sees his confidence th a t success of theory is not coupled either at th e beginning or a t the end to sheer experim ental facts alone. Thus he w rites to Besso in M arch 1914, before th e first eclipse expedition to test th e conclusions of G eneral R elativity: “Now I am fu lly satisfied, and I do not doubt any m ore the correctness of the w hole system, m ay the observation of the eclipse succeed or not. The sense of th e thing (V ern u n ft der Sache) is too evident”. And at a later tim e Einstein com m ented on th e fact th a t th e re rem ains up to ten percent discrepancy betw een the m easure­ m ent of the deviation of light by th e su n’s field and the calculated effect: “For th e expert this thing is not p articu larly im portant because the m ain significance of th e theory does not lie in the verification through little effect, b u t rath e r in the great sim plification of the theoretical basis of physics as a w hole” (Seeling, p. 195). Or again Ein­ stein rep orts in his notes on the origins of the general theory (Ideas

and Opinions, p. 287) th a t he “was in the highest degree amazed at

its existence (of th e law of the equality of in ertial and gravitational mass)”, b u t th a t he “had no serious doubts about its strict validity, even w ithout knowing the results of the adm irable experim ent of Eotvos...”.

Again, w riting to Besso in 1921 on the verifications of general relativ ity theory to this point: “I had not a m om ent’s doubt th a t it m ust be this w ay”. And on C hristm as Day 1925, he received th e follo­ wing cable from America: “P resid ent M iller, Am erican Physical So­ ciety, announces discovery of eth er drift. Says «my w ork annuls se­ cond postulate Einstein theory.» Please cable collect 200-word opinion t id e (Radioactivitcht und Electrizitat, vol. 4 Issue No 4), Einstein d is­ cusses the exp erim en ts by W. Kaufm ann. On page 436 ff. he cites K aufm ann’s paper in th e Annalen der Physik , 1906, 19, “Concerning the Construction of the E lectron”, reproduces som e of his figures, and says that W. Kaufm ann, working “w ith adm irable care”, had found the relation of the radii of curvature of the path of fast electrons in pure electric and pure m agnetic fields. There is a sy ste­ m atic sm all d ifference from E instein’s relativity theory for the results as K au f­ m ann had pointed out. Einstein says that Kaufm ann’s calculations are free of error. But “w hether there is an unsuspected system atic error or w hether the foundations of relativity theory do not correspond w ith the facts one w ill be able to decide w ith certainty only if a great variety of observational m aterial is at hand”. The series of electron m otion given by Abraham and in B ucherer’s 1904 book, Einstein says, do give predictions considerably c l o s e r to the curve. But then he adds: “H ow ever, in m y opinion both theories have rather a sm all probability because their fundam ental assum ptions concerning the m ass of m oving electrons are not explainable in term s of theoretical system s w hich embrace a grea­ ter com plex o f phenom ena” (p. 439).

A s is characteristically th e case in an Einsteinian objection, the a d h o c character of a theory is found objectionable, even though the “experim ental fa cts” at that tim e very clearly seem to favor the theory of Einstein’s oppo­ nents.

In flu e n c e s on E in ste in ’s E a rly W o rk 2 4 3

press rates. David Dietz, NEA Service, Inc.” . T here app aren tly was no answ er, b u t on th e sam e day Einstein w rote to Besso, “I th in k th a t the M iller experim ents re st on an erro r in tem perature. I h av e not taken them seriously for a m in u te”. Again, on th e 14th of M arch 1926, in a le tter to Piccard, Einstein says apropos th e M iller experim ents, “I believe th a t in th e case of M iller th e whole spook is caused by tem p eratu re influences (air)” .15

In th e end, th e epistemological th read ru nn in g through E instein’s whole work, from th e beginning, a th read th a t connects him w ith certain aspects of th e G erm an school of thought, as p articu la rly exem ­ plified in F oppl’s text, is ju st this p articu lar balance h e struck betw een th e dem ands of theory and of the w orld of detailed experience. As Einstein p u t it in a h ith erto unpublished addendum to his A u tobio­

graphical Notes, “Everything conceptualizable is constructive and not

derivable in a logical m anner from im m ediate experience. T herefore we are in principle com pletely free in the choice of those fundam ental conceptions upon w hich we found our rendition of th e w orld. Eve­ rything depends only on this: to w h at ex ten t our construction is sui­ table for bringing order into th e a p p aren t chaos of th e w orld of expe­ rience”. As the le tters and m anuscripts show even b etter th a n Ein­ stein’s published works, he constantly saw his task as being, in large part, the subjugation of th e w orld of m ere, im m ediate experience by m eans of fundam ental thought. We, who have come h ere to celebrate his achievem ents, are indeed th e beneficiaries of his lonely and grand message.

And w hile we have looked a t some of th e docum ents w hich Ein­ stein surely did not in itially m ean to be used for historic research, we can nevertheless be sure th a t Einstein w ould have understood and not objected to th is purpose. For as he w rote to Besso (30 Novem ber 1949): “W hen I w rite you something, you can show it to anyone you like. I have long been above m aking of secrets”. And in another u n p u b li­ shed m anuscript (No. 17, undated, not before 1931): “Science as an 15 D espite m any entreaties from scientists and the press, Einstein only gave very little public evidence of interest in the M iller experim ents. There is one letter from M iller to Einstein (of 20 May 1926) show ing that Einstein had w ritten to M iller and that they had m et before, also that Einstein had told M iller “a d iffe ­ rence of a tenth degree in the tem perature of the air along th e ligh t path in the arms of the interferom eter w ould produce a displacem ent o f th e frin ges of the amount observed”. M iller w as rendering E instein ’s query, apparently, but adds that “very elaborate precautions have been taken to elim inate such an effect of tem perature”. It is ironic that the splendid and elaborate analysis of R. S. Shan- kland and his colleagues in 1955 traced M iller’s observed effects p recisely to this source. Indeed, in a letter of 24 February 1963 to Shankland, Miss Dukas report? that the fam ous remark Raffiniert ist der Herrgott, aber boshaft ist Er nicht was made by Einstein at a reception in 1921 after a lecture in Princeton when Einstein w as asked his v iew s about the M iller experim ents. The rem ark illustrates Einstein’s confidence concerning the kinds o f exp eriences N ature w ould “a llow ”.

existing, finished (corpus of knowledge) is the most objective, most unpersonal (thing) hum an beings know, (but) science as som ething co­ ming into being, as aim, is ju st as subjective and psychologically con­ ditioned as any other of m an’s effort...”. And th a t aspect, he w ent on to say, one should certainly “perm it oneself also” . H appily, he and his friends and colleagues have done ju st th at. They have left us the record of “science coming into being” and th ereb y th ey have enriched our understanding for all time.

A C K N O W L E D G M E N T S

I w ish to acknowledge w ith g ratitu d e the help received from the Trustees of th e A lbert Einstein Estate, and p articu larly from Miss Helen Dukas. P artia l financial support for cataloguing the documents was furnished by the Rockfeller Foundation. The In stitu te for A dvan­ ced S tudy at P rinceton and its D irector, Dr. Oppenheim er, have been most hospitable throughout this work, including th e period which I spent as a M ember at th e In stitu te during a sabbatical leave.

E arlier (unpublished) d rafts have been presented as invited papers at the an n u al m eeting (Jan u ary 1965) of th e A m erican Physical Society in New York, and a t th e International Congress on R elativity (Ju ly 1965) in London.