Scott A. Walter

scott.walter [at] univ-lorraine.fr

Published in Karl-Heinz Schlote and Martina Schneider, eds,
*Mathematics Meets Physics*, Frankfurt am Main: Harri Deutsch,
2011, 213-239.

In studies of the emergence of relativity theory, historians have
sought to characterize the reception of relativist ideas with respect
to national communities of physicists and mathematicians, in an effort
to reveal underlying features of these communities, such as their
openness to new ideas, and their capacity for change. Stimulating this
activity are the basic publication counts, that tell us that the
reception of relativity theory in academic journals varied markedly
from one country to another. Periodicals based in Germany accounted for
roughly half of all relativist publications before 1916, while Germany-based authors published two of
every five articles on relativity during the same period, and made up
two-fifths of the total number of scientists (one hundred)
contributing to relativity theory. France, the fifth most active
country from a quantitative point of view, accounted for seven percent
of relativist articles, and counted eight relativist scientists, or about a twelfth
of the total.^{1}^{1}Of 662 publications on relativity theory in
periodicals between 1905 and 1916, 323 were published in Germany;
see Walter (1996, Tables 4.3–4).

Examination of the content of these publications and their context of
production allows for a finer-grained understanding of the differences
revealed by quantitative analyses, and gives rise to theories of
reception. For example, scholars of the reception of relativity theory
in Germany and England have proposed explanatory models in which the
details of post-secondary training in physics are seen as
decisive.^{2}^{2}Pyenson 1987;
Warwick 2003.
Historians of French physics consider the
muted reception of relativity in France as a consequence of a
pervasive positivist outlook among French scientists, which would have
favored the development of mathematics, while leaving little
intellectual space for the distinct melange of experimental acumen,
physical and mathematical reasoning that characterized the work of a
Boltzmann, a Lorentz, or an Einstein.^{3}^{3}See Paty
(1987, 115),
Biezunski (1987, 184), and
Pestre (1992, 117).
On French isolationism in electrodynamics (and its exceptions), see Darrigol
2000, 352.

Attention to the conceptual foundations of early relativist
publications reveals a marked difference in approach on the part of
two contributors in particular: Henri Poincaré and Albert
Einstein. Understanding this difference in approach has occupied
historians and philosophers of science for over half a century,
without reaching a consensus on its significance for the history of
physics.^{4}^{4}A balanced overview of the ‘‘mystery of the
Einstein-Poincaré connection’’ is provided by
Darrigol (2004).
Poincaré’s philosophical writings,
published for the most part prior to the discovery of relativity,
weigh heavily in these analyses, and according to one commentator,
constituted an obstacle to the reception of Einstein’s theory of
relativity in France until the 1920s.^{5}^{5}See
Borella 2002. By the same token,
Poincaré’s philosophical writings ought to have benefited his theory
of relativity, but the above-mentioned publication counts indicate
that they did not do so, either in France or elsewhere in the world.

The outlines of an alternative account of French contributions to relativity during the years from 1905 to 1912 are drawn in this paper. Poincaré’s intellectual and institutional leadership in French physics at the turn of the twentieth century is reviewed, and related to the emergence of Paul Langevin as his successor. Drawing on quantitative data and previously-unexploited manuscripts from Parisian archives, the paper compares the fate in France of Poincaré’s theory of relativity to that of the Einstein-Minkowski theory of relativity championed by Langevin, and links these events to Langevin’s rise to leadership of French theoretical physics.

Compared to the situation of French physics in the first decades of the nineteenth century, in 1898 the future did not appear promising to Henri Poincaré. His pessimism stemmed from a perceived mismatch between the cognitive habits of the French scientist and the turbulent state of theoretical physics brought about by the discoveries of the past decade, including the null-result of the Michelson-Morley ether-drift experiment, the discovery of x-rays, the electron, the Zeeman effect, and radioactivity. A certain boldness was called for to explain such results, and Poincaré feared that the French were not up to the task at hand, as he expressed it in an official report to the Paris faculty of science:

The French mind, avid of clarity and logic, is repugnant of excessively temerarious adventures.

A new type of physicist was called for, according to Poincaré, in
order to ‘‘discern the simplicity of laws beneath the complexity of
phenomena’’.^{6}^{6}Paris faculty of science, pièces annexes aux
procès-verbaux, 1883–1903, 78–79, French National Archives. A
transcription
is available from the
Poincaré correspondence
website. The type of physicist Poincaré had in mind, although
probably not the archetype, was Jean Perrin, whose candidacy he
evaluated for a lectureship in physical chemistry on the Paris faculty
of science. To some extent, Poincaré may have described here his own
approach to the laws of physics, although his prowess in mathematics
clearly set him apart from even the most mathematically-sophisticated
of his colleagues in physics.

Paris did not yet dispose of a chair in theoretical physics *per
se*, and would not create one until 1928, when the Rockefeller
Foundation volunteered to finance a new
institute.^{7}^{7}Siegmund-Schultze 2001.
The first French chair nominally devoted to theoretical physics dates from
1894, when the faculty of science in Bordeaux hired Pierre Duhem. This
is not to say that theoretical physics was neglected in Paris. At the
Paris faculty of science, the chair of probability calculus and
mathematical physics, dating from 1834, was devoted to the
subject. Poincaré held this chair for a decade, from 1886 to 1896, and
single-handedly brought French theoretical physics to international
attention. The work in theoretical optics and fluid mechanics by his
successor Joseph Boussinesq, however, found little echo outside of
France.^{8}^{8}Darrigol 2005, 239.

For the sake of comparison, across the border, a modest institute for
theoretical physics was created at the University of Berlin in 1889,
at the behest of Hermann von Helmholtz, and by the turn of the
century, such institutes had been created in Königsberg, Leipzig,
Göttingen and Munich.^{9}^{9}Jungnickel & McCormmach
1986, vol. 2, 254.
At the turn of the twentieth
century, only two of these institutes were led by full professors: Max
Planck in Berlin, and Woldemar Voigt in Göttingen.^{10}^{10}Schlote
2004, 86. There were other outstanding theorists
in Germany, notably Paul Drude, Willy Wien, and Arnold Sommerfeld, but
some of these theorists felt Germany had lost its preeminence in the
field since the time of Gustav Kirchhoff.^{11}^{11}Jungnickel &
McCormmach 1986, vol. 2, 159. Since the death of
Heinrich Hertz in 1894, and Ludwig Boltzmann’s departure from Munich
the same year, the brilliance of H. A. Lorentz in Leiden and Boltzmann
in Vienna had cast shadows over their counterparts in Germany and France alike.

At least one theorist in Paris was prepared to meet the challenge
posed by the recent results of experimental physics:
Henri Poincaré. The fact that after 1896, Poincaré no longer occupied a chair of
mathematical physics did not prevent him from lecturing and theorizing in
this domain, just as earlier, he cultivated subjects of pure
mathematics (function theory, algebraic topology), and celestial
mechanics while nominally a professor of probability calculus and
mathematical physics. Beginning in the late 1880s, Poincaré helped introduce Maxwell’s electromagnetic
theory to French readers, and in the late 1890s, he exhibited a keen
interest in Lorentz’s theory of electrons.^{12}^{12}See Darrigol
2000. Interest in Lorentz’s theory grew rapidly
when Lorentz used it to explain the splitting of Sodium D lines in an
external magnetic field, an unexpected phenomenon discovered in 1896
by Lorentz’s former student, Pieter Zeeman (1865–1943). Poincaré
communicated to the Paris Academy of Sciences a paper by Zeeman
(1897) describing his discovery, and soon engaged
with the explanation of the effect offered by Lorentz. Others in
France soon took up studies of the Zeeman effect, including Alfred
Cornu (1841–1902), Poincaré’s former physics professor at the *École
polytechnique,* and Alfred Liénard (1869–1958), a former student of
Poincaré’s, who taught mathematics and physics at the School of Mines
in Saint-Étienne.

Poincaré’s engagement with electrodynamics was enduring, and remarkably
innovative, featuring applications of sophisticated mathematical
methods (complex analysis, group theory), and the
reformulation of key concepts of Maxwell’s electromagnetic theory and
Lorentz’s electron theory, along with applications of these methods
and theories. For example, in the 1890s, Poincaré was among the first to
use retarded potentials in Maxwell’s theory, and proposed the first
electromagnetic theory of diffraction, which was soon
extended by Arnold Sommerfeld. His demonstration of the recurrence
theorem was recognized to have fundamental repercussions on physics,
particularly for kinetic theory. He also provided a theory of multiple
resonance for Hertzian oscillations, and the first exact
solution of Maxwell’s equations for charged particles in a strong
magnetic field.^{13}^{13}Poincaré 1890,
1891b,
1891a,
1892,
1897b.

By the turn of the century, Poincaré’s contributions to physics had
won the admiration and respect of his peers across Europe and in the
USA. Poincaré was one of only two Frenchmen invited to contribute to a
volume in honor of G.G. Stokes in 1899, alongside
Cornu.^{14}^{14}See Cambridge Philosophical Society,
ed. (1900). The next year, Poincaré was one of the
three Frenchmen on the scientific committee of the international
physics congress organized in Paris by the French Society of Physics,
and presided by Cornu. One of ten vice-presidents of the physics
congress, Poincaré presided the international congress of
mathematicians, which conveniently took place in Paris the same week
in August.^{15}^{15}C.-E. Guillaume and L. Poincaré,
eds. (1900). The following year, Poincaré was
elected vice-president of the French Society of Physics, and in 1902,
served as its president. A few years later, the Society made Poincaré
one of its ten honorary members.^{16}^{16}Three other French
physicists had attained this status by 1909: Jules Violle, Gabriel
Lippmann, and Émile-Hilaire Amagat; see *Bulletin de la société
française de physique* (1908), p. 3*.

This recognition from Poincaré’s peers in physics did not mean that his
authority in physics went uncontested, either at home or abroad. There
were those, like the Scottish natural philosopher P. G. Tait, who found his
lectures on mathematical physics to be excessively analytical, and unreliable on foundational
issues.^{17}^{17}See the review by P. G. Tait (1892)
of Poincaré’s *Thermodynamique* (1892),
reedited with annotations (and Poincaré’s replies) in Walter et al., eds,
eds (2007,
§ 62). Near the end of the decade, when
Lorentz explained the Zeeman effect on the basis of his theory of electrons, Poincaré proposed an
alternative formula, which was mathematically sound, but for Lorentz, uncompelling
from a physical standpoint.^{18}^{18}Poincaré 1897a; Buchwald
1985, 226.

In France, Poincaré’s views on questions of mathematics or physics
were very rarely challenged in public. The case of Marcel Brillouin
(1854–1948) is instructive from this perspective. With doctoral
degrees in mathematics and physics, Brillouin was named associate
professor at the *École normale supérieure* in 1887. In the
early 1890s, Brillouin dutifully pointed out what he thought was an
error in the first edition of Poincaré’s lectures on Maxwell’s theory,
concerning Hertzian waves. Poincaré’s gentle private lesson led
Brillouin to retract his criticism.^{19}^{19}See Poincaré’s
correspondence with Brillouin in Walter et al., eds,
2007,
§ 12;
Brillouin 1891a,
1891b. In 1900, Brillouin replaced Joseph
Bertrand as professor of general and mathematical physics at the
*Collège de France*, and when a new edition of Poincaré’s
*Électricité et optique* appeared in 1901, Brillouin had only
high praise for it.^{20}^{20}Poincaré 1901;
Brillouin 1901.

At the turn of the century, Poincaré’s physical acumen was severely
tested, when Gabriel Lippmann’s doctoral student, Victor Crémieu
(1872–1935) published a result casting doubt on Rowland’s effect,
whereby, in line with Maxwell’s theory, convected electricity
produces a certain magnetic effect. Poincaré wrote the official report
on Crémieu’s thesis, communicated several of his results to the Paris
Academy of Sciences, and argued that if the result was confirmed,
Maxwell’s theory would have to be abandoned. None of Europe’s leading
physicists gave any credence to Crémieu’s findings, which if true,
would have overturned the electron theories of Lorentz and Larmor, as
well as Maxwell’s theory. In France, Brillouin shared Poincaré’s high
opinion of Crémieu’s results, but Poincaré’s colleague at the
Sorbonne, the physicist Henri Pellat (1850–1909) remained doubtful,
as did Poincaré’s former teacher at the *École polytechnique,* Alfred
Potier (1840–1905).

When Harold Pender, who was Rowland’s last doctoral student, confirmed
Rowland’s effect in Baltimore, Poincaré saw to it that Pender and his
equipment were transported to the Edmond Bouty’s laboratory in Paris,
in order to perform experiments side-by-side with Crémieu. Pender
emerged victorious from the encounter; to the
French Society of Physics Pender explained not only how the Rowland effect manifested itself,
but why Crémieu’s apparatus had failed to detect it.^{21}^{21}Pender &
Crémieu 1903. Historical accounts include Indorato
& Masotto 1989, and Walter et al.,
eds. 2007,
§ 17.
The result of the encounter
suggests that Poincaré had misjudged the situation; nonetheless, he obtained what
he required as a theoretical physicist: an experimental decision
between Maxwellian and non-Maxwellian electrodynamics.

Pender and Crémieu’s account of their parallel investigations
of convected electricity appeared in a leading journal of French physics: the
*Journal de physique théorique et appliquée* (*JPTA*),
founded in 1872. During the first decade of the twentieth century, the
*JPTA*’s editorial board counted two professors of physics
from the Paris faculty of science, Edmond Bouty and Gabriel Lippmann,
along with a pair of senior theorists, Alfred Potier and Élie Mascart,
neither of whom survived the decade. Filling out the editorial board
were a trio of associate editors, former students of the *École
normale supérieure:* Lucien Poincaré, Bernard Brunhes, and Georges
Sagnac; and one non-Normalien associate editor, Marcel Lamotte, an
associate professor of physics at Clermont-Ferrand, who like Brunhes
had helped edit Poincaré’s volumes on mathematical physics in the
early 1890s.

The *JPTA* did not publish contributions in theoretical physics
that involved sophisticated mathematical elaboration, in order to
remain accessible to ‘‘isolated’’ physicists, which is to say, those
out of range of science faculties and their libraries.^{22}^{22}This
was the policy announced by the *JPTA*’s founder,
J.-C. Almeida, in the first issue of the review. This approach
manifested itself in the selection of articles for publication, and in
the abstracts of articles published abroad. More often than not, when
an article featured a mathematical argument, the *JPTA*
abstract revealed this fact alone, with no judgment of merit or
meaning. Consequently, readers were ill-informed of current work in
theoretical physics, beyond what might be guessed from reading the
name of the author, and the title of the contribution.

There were other venues in France for publishing research in
theoretical physics, including the *Annales de chimie et de
physique* (or *ACP* for short), *Le Radium*, the
*Annales scientifiques de l’École normale supérieure*, and the
*Journal de mathématiques pures et appliquées*. The latter two
journals attracted few papers on physics, unlike *Le Radium*,
founded in 1904 by H. Becquerel, P. Curie, E. Rutherford,
Ch.-E. Guillaume and others. *Le Radium* effectively competed for
readers with the *JPTA*, providing translations of German and
French contributions, and abstracts of various periodicals, until the
two journals fused in 1920. The *ACP*, founded in 1816, attracted
significant communications in the first decade of the twentieth
century from Paul Langevin, Jacques Hadamard, Marcel Brillouin, and
the latter’s student, Jean Perrin. At the beginning of the decade, the
*ACP* was directed by the venerable trio of Marcelin Berthelot,
Élie Mascart, and Henri Moissan, none of whom were still alive in
1910. At the end of the first decade, a different trio of editors
directed the *ACP*: the chemist Albin Haller (1849–1925) and his
two colleagues on the Paris faculty of science, Lippmann and Bouty,
who continued to edit the *JPTA*.

During this period the *ACP* published doctoral theses in
physics, as well as extended summaries of experimental and theoretical
investigations. Two examples may be mentioned here. One of these is
the Swiss theorist
Walter Ritz’s long memoir, ‘‘Critical investigations in general
electrodynamics’’, in which Ritz gave an overview of the work of
Lorentz, Poincaré, Einstein, and others, and sketched an alternative
approach to the electrodynamics of moving bodies, based on retarded
potentials and a principle of superposition.^{23}^{23}Ritz
1908; Martínez 2004. Another
is Perrin’s ‘‘Brownian motion and molecular reality’’, where he
presented the results of experiments that confirmed Einstein’s formula
for Brownian motion of a particle in a fluid, work for which Perrin
was awarded the Nobel Prize in physics in 1926.^{24}^{24}Perrin
1909; Nye 1972.

The only other publishing outlet for research in theoretical physics
in France, but one more widely cited than the *ACP* or any other
French scientific journal, was the organ of the Paris Academy of
Sciences, the *Comptes rendus hebdomadaires* (hereafter
*CRAS*). This was where Poincaré published most often, averaging
nine papers a year throughout his career, including a signal
contribution to relativity theory on 6 June 1905. The *CRAS*
enforced a page limit on its contributors, and Poincaré’s four-page
summary was no exception to the rule. The memoir summarized in the
*CRAS* appeared in the *Rendiconti del Circolo matematico di
Palermo*, a journal in which since 1888 Poincaré had published on
the theory of differential equations, analytical mechanics, and
algebraic topology. Until 1906, Poincaré published all his articles on
physics (excluding notes in the *CRAS*) either in foreign
journals, or in a Paris-based journal of electrical engineering,
*Éclairage électrique*, on the editorial board of which he served
beginning in 1899.

One consequence of this habit was that until 1906, Poincaré’s latest
research in theoretical and applied physics was known best to French
electrical engineers, and readers of *CRAS* and foreign research
journals. Students of physics knew Poincaré best through his lectures
on mathematical physics, published in thirteen volumes (not counting
translations to German, or reeditions). The effect of these volumes was
described somewhat breathlessly by the mathematician (and former
Poincaré student) Maurice d’Ocagne, for whom Poincaré had, in addition to
being the world’s premier theoretical astronomer,

…carved for himself an unequaled position as a theoretical physicist, projecting a new light, emanating from the most unexpected sources, upon every part of mathematical physics: heat, optics, electricity, elasticity, capillarity, etc. …. He has covered everything, renewed everything, extended everything. […]

What is more, there are many experimentalists who make no mistake in recognizing all they owe to the theoretical views introduced to science by Mr. Poincaré, and who have quite often reoriented their laboratory investigations to the great benefit of the general advance of our knowledge. (Maurice d’Ocagne 1909, 541)

What d’Ocagne’s remark suggests most clearly is the source of
Poincaré’s preeminence in French theoretical physics, and his
influence on research agendas in experimental physics. Physicists who
acknowledged such an influence included, among others in France, Henri
Becquerel, René Blondlot, Gustave Le Bon, Paul Langevin, Georges
Sagnac, Alfred Perot, and Victor Crémieu; in Geneva, Lucien de la Rive
and Édouard Sarasin; in Kristiania (now Oslo), Kristian
Birkeland.^{25}^{25}Poincaré’s interaction with experimental
physicists is well-documented in his correspondence; see
the introduction
to Walter et al., eds,
2007.

While Poincaré’s influence on the agenda of experimentalists is
apparent, what can be said of his mark on the agenda of theorists?
Some of the aforementioned experimentalists also wore a theorist’s cap
on occasion, like Birkeland, Langevin, and Sagnac. All three of these
physicists published on subjects stemming from those taken up earlier
by Poincaré, notably in the domains of Hertzian waves and electron
theory; all were former students of Poincaré. According to
another former student of Poincaré’s, Arthur Korn, there was not a
single physicist anywhere whose work had not found fundamental
stimulation in Poincaré’s lectures.^{26}^{26}Korn
1912.

Poincaré is often characterized by historians as a leading critic of
theories of physics, and indeed, his lectures in mathematical physics
offered a magisterial discussion of rival theories in the several
branches of physics, that compared relative strengths and
weaknesses.^{27}^{27}Such a characterization is offered by Darrigol
1995,
2000.
His lectures on Maxwell’s theory
were eagerly read in Germany (in German translation), and exercised a
profound influence on the first German textbooks on Maxwellian
electrodynamics.^{28}^{28}See Darrigol 1993;
2000, 354. Some of his non-technical analyses were
reedited for a larger audience in the four anthologies of his
epistemological writings on mathematics and the exact sciences edited
by 1913, which were widely read and appreciated by both specialists
and the general reading public alike.^{29}^{29}According to Lebon
(1912, 84), the first of these anthologies, entitles
*La science et l’hypothèse* (1902), sold twenty thousand copies
by 1911. On the composition of Poincaré’s anthologies, see Rollet
(2001, chap. 4).
Poincaré’s critical acumen in
theoretical physics was appreciated by his peers, including Joseph
Larmor, who contributed a preface to the English translation of the
first of the anthologies: *Science and Hypothesis*.

On an international level, with the discovery of x-rays, the electron
and radioactivity in the closing years of the nineteenth century, the
physics of charged particles filled the pages of physics
journals. French prowess in experimental microphysics received
international recognition following work by Henri Becquerel and the
Curies on radioactive matter, and René Blondlot on electrical
convection, although the latter’s reputation was later tarnished when
what he called ‘‘N-rays’’ proved spurious. On the theoretical side,
Poincaré and Alfred Liénard were among the first theorists to
contribute to Lorentz’s electron theory, and to apply it to dispersion
phenomena and the Zeeman effect.^{30}^{30}See Buchwald
1985. Outside of France, respected theorists at
the turn of the twentieth century included, first and foremost,
Lorentz in Leiden, Boltzmann in Vienna, Joseph Larmor and J.J. Thomson
in Cambridge, Ernest Rutherford in Montreal, Paul Drude in Giessen,
Max Planck in Berlin, Sommerfeld in Aachen, Wilhelm Wien in Würzburg,
Woldemar Voigt, Emil Wiechert, Max Abraham, and Walther Nernst in
Göttingen.

Critical analysis of physical theories was an activity at which
Poincaré was skilled and accomplished, and for which he was amply
rewarded. His contributions to physics, however, went well beyond
writing textbooks and critiques of others’ work, into the creative
realm of theory construction. Among the theoretical physicists
mentioned above, Sommerfeld and Abraham found significant inspiration
in Poincaré’s theories of physics. Sommerfeld’s electromagnetic theory
of diffraction of plane waves (1896) improved on Poincaré’s
groundbreaking paper of 1892, while Abraham borrowed on the
Frenchman’s conception of electromagnetic momentum to form his theory
of electron dynamics.^{31}^{31}Poincaré 1892;
Sommerfeld 1896,
2004. On Abraham’s and
Planck’s theories see Miller 1980,
1981. Last
but not least, in the summer of 1907, Hermann Minkowski took up the
elements of Poincaré’s four-dimensional approach to relativity theory,
in what became a game-changing theory of physics: the theory of
spacetime.^{32}^{32}Poincaré 1906;
Minkowski 1908;
Walter 2007,
2008.

The latter three contributions were among those cited in support of an
ultimately unsuccessful campaign to award Poincaré the Nobel prize in
physics in 1910, in addition to work on the
propagation of Hertzian waves, and the theories of vibrating plates, rotating fluid
masses, and electron stability.
The failure of Poincaré’s
Nobel campaign reflects in part the still-uncertain status of the theory of
relativity in 1910, and in fact, the Nobel committee never awarded a
prize in recognition of the discovery of special relativity. In
context, it is curious that a Nobel prize nomination
emanating from the Paris Academy of Sciences in January 1910, and
including among its signatories the Academy’s permanent secretary for
the mathematical sciences, Gaston Darboux, should feature work ‘‘of
the highest importance’’ by Poincaré on the principle of
relativity.^{33}^{33}See Darboux et al. to the Nobel Committee, ca. 1
January 1910, transcribed and annotated in Walter et al.,
eds, 2007,
§ 62.
On the organization of the 1910
campaign, see Ph. Nabonnand’s notes to the correspondence between
Poincaré and G. Mittag-Leffler (Nabonnand, ed, 1999).
On 5 June 1905, Poincaré’s precis of relativity theory appeared in the
*Comptes rendus* of the Academy, announcing a longer work
published in the Palermo *Rendiconti*.^{34}^{34}Poincaré
1905,
1906.
Afterwards, no notes were
published by anyone on this subject in the *Comptes rendus* until
7 February 1910, when results of cathode-ray deflection experiments by
Charles-Eugène Guye and Simon Ratnowsky in Geneva appeared, tending to
confirm Lorentz’s predictions of velocity-dependent
mass.^{35}^{35}Guye and Ratnowsky (1910), originally
submitted on 10 January 1910, and withdrawn by Guye, ostensibly to
permit the inclusion of new data (Guye to Gaston Darboux, 30 January
1910, Archives of the Academy of Sciences, session folder, 7 February
1910).
Contrary to Darboux’s description, the publication record suggests
that the theory of relativity was of little importance to French
science, at least until February 1910.

What happened to the theory of relativity in France during the latter half of the first decade of the twentieth century? And how did Einstein’s theory come to prominence in France in 1911? In the next section, I show that while Lorentz’s theory was often discussed, alternative theories remained nearly invisible in France until 1911. The situation changed in 1911, as the final section will show.

In the scientific centers of Western Europe, physicists did not
distinguish at first the theories of Lorentz, Poincaré, and
Einstein. Of these three founders of relativity theory, Poincaré
alone took care to identify the differences between his theory and
that of Lorentz; Einstein’s theory had not yet been published when he
wrote his memoir. A year later, after Einstein’s theory had been aired
in the *Annalen der Physik*, Poincaré took care to explain to his
students at the Sorbonne how his theory of relativity differed from
that of Einstein, albeit without ever mentioning Einstein or his
theory.

Poincaré performed a curious thought experiment for his students, in
which a pair of inertial observers, one at rest, the other moving away
in a straight line at constant speed, describe the form of a locus of
light at a certain instant of time. An observer at rest with respect
to the ether judges the light locus to have the form of a sphere, the
radius of which increases with the speed of light. Observers in motion
with respect to the ether, Poincaré explained, would conclude that the
light locus at any instant of time (as determined via co-moving
light-synchronized clocks) is represented by an ellipsoid of rotation,
elongated in the direction of observer motion with respect to the
ether. In Einstein’s theory, by contrast, the light locus at any given
instant of time (as determined via co-moving light-synchronized
clocks) is always represented by a sphere.^{36}^{36}See my forthcoming
paper in *Einstein Studies*. For alternative explanations of
Poincaré’s light-ellipsoid, see Cuvaj (1970, 74) and
Darrigol (2006, 17–19).
After presenting his view
of relativity to his students, Poincaré published his light-ellipsoid
theory of relativity in France’s leading popular-science biweekly, the
*Revue générale des sciences pures et appliquées*. He did not
mention Einstein’s theory, and in the *Revue générale* no one
else did, either, until Maurice Lémeray wrote of ‘‘Einstein’s
beautiful results’’ four years later.^{37}^{37}Poincaré
1908;
Lémeray 1912.

Poincaré’s silence with respect to Einstein’s theory has been the
subject of much historical speculation, and will not
concern us here. Instead, let us ask why no one else in France saw fit
to mention Einstein’s theory in print before 1911. And to begin with,
let us investigate why one person in particular, Paul Langevin, did
not mention Einstein’s theory in print before 1911. Recall that in
1905 Langevin proposed an electron theory similar in some respects to
that of Alfred Heinrich Bucherer, featuring an electron model of constant volume,
and velocity-dependent shape, and that Poincaré showed Langevin’s
theory to be incompatible with relativity. Langevin acknowledged
Poincaré’s judgment of his theory, but did not give it up
until the experimental results presented by A.H. Bucherer in
September 1908 persuaded him to do so.^{38}^{38}See Langevin’s
*Notice sur les travaux scientifiques* (1908, 35). To
put it briefly, until the fall of 1908 there were several plausible
alternatives available to relativity theory, some of which enjoyed,
like Abraham’s rigid-electron theory, better empirical support in some
tests than did the theory of relativity.^{39}^{39}On the choice
between alternative theories of the electrodynamics of moving bodies
circa 1905, see Darrigol (2000, 391).

Einstein was not unknown in French physics circles, and his name was
cited in contexts other than relativity in the period from 1905 to
1910. In kinetic theory, for example, Einstein’s formula of 1905 for
specific heat was promoted by Jean Perrin in 1908, and referred to
simply as ‘‘Einstein’s formula’’. A look at the abstracts published by
the *JPTA* from 1905 to 1911 reveals that the ‘‘Abraham theory’’
of the electrodynamics of moving bodies was mentioned twice, the
‘‘Einstein theory’’ three times, and the ‘‘Poincaré theory’’ or
‘‘Lorentz-Poincaré theory’’ four times. One notices that Poincaré’s
theory never stood alone in these abstracts, but was always
accompanied by a reference to Lorentz’s theory, which was mentioned
much more often than any other, garnering a total of twenty-two
independent occurrences.

Also, the paucity of detail in *JPTA* abstracts on relativity and
electron theory, compared with that provided for other subjects,
suggests a certain lack of comprehension or interest on the part of
the abstract writer. A general ignorance of and disinterest in
relativity theory was not unique to French physicists, as even in
Germany, publication numbers remained modest in this area until 1909,
when they began to climb rapidly (see Fig. 2). One difficulty for
relativity theory was its poor performance in electron-deflection
experiments, which led many to believe that relativity theory was
empirically untenable. In a discussion of electron theory in 1906, for
example, Paul Ehrenfest considered Lorentz’s theory to have been
definitively disproved by experiment, and Ehrenfest’s opinion was duly
related by Léon Bloch for readers of *Le
Radium*.^{40}^{40}Ehrenfest 1906; *Le Radium*
3, 1906, p. 148. In such circumstances, it is a wonder that any
physicist bothered learning relativity theory before the
end of 1908.

After an experimental confirmation of relativity theory was announced
in September 1908, the incentive to learn the theory, and to
investigate its consequences naturally increased. What is curious in
the French context is that apart from Poincaré, no other physicist
took up relativity, until Paul Langevin lectured on the subject at the
Collège de France in 1910–1911. According to Poincaré’s own report,
he pursued a relativistic theory of elastic collisions, but deemed his
results unworthy of publication. As he explained it to a Berlin
audience in late 1910, the lack of such a theory was one reason why
the new mechanics of relativity could not be considered ‘‘definitively
grounded’’.^{41}^{41}Poincaré 1910, 115–116. In
front of French audiences, Poincaré offered a different message,
designed to reassure those worried about overturning Newtonian
mechanics: the ‘‘old mechanics’’, Poincaré announced, was still the
one for ‘‘our practical life and our terrestrial
technology’’.^{42}^{42}‘‘Quoi qu’il en soit, d’ailleurs, elle restera
la mécanique des vitesses très petites par rapport à la vitesse de
la lumière, la mécanique donc de notre vie pratique et de notre
technique terrestre.’’ Plenary lecture, 3 August, 1909, to the
meeting of the French Association for the Advancement of Science in
Lille (Poincaré 1909).

Poincaré’s measured consideration of the theory he helped create may
have dissuaded a few junior French theorists from following in his
tracks, but not Paul Langevin.^{43}^{43}On Langevin’s relation to
Poincaré and Einstein, see Paty (2002). As a
student of Poincaré’s 1896 lectures on the elastic theory of light,
Langevin had learned how a certain theorist referred to as
‘‘Somerset’’ extended Poincaré’s theory of polarization by
diffraction.^{44}^{44}Fonds Langevin, Notebook ‘‘Poincaré Élasticité
et optique III 1896’’, carton 123, Bibliothèque de l’École
supérieure de physique et de chimie industrielle, Paris. In a later
appreciation of Poincaré’s contributions to physics, Langevin
recalled Poincaré’s lectures on optics, which showed how Sommerfeld
‘‘brilliantly followed a path’’ opened by Kirchhoff and Poincaré via complex analysis; see Langevin (1913, 691).
Ten years later, on the strength of this work, and more recent
contributions to electron theory, this same theorist – better known
as Arnold Sommerfeld – was named to the chair of theoretical physics
in Munich, formerly held by Boltzmann.^{45}^{45}Eckert
1984. Sommerfeld was in charge of the physics
volume of Felix Klein’s planned six-volume *Encyclopedia of
Mathematical Sciences with Applications*, the first entries of which
appeared in 1903.^{46}^{46}See Eckert and Märker, eds,
2001, vol. 1, p. 40.
On 16 April, 1906, Sommerfeld informed Langevin
that Klein had agreed to let him co-edit
the French version of the physics volume with Jean Perrin, a task that would occupy the
two Frenchmen for nearly a decade.^{47}^{47}Fonds Langevin, op. cit.,
carton 76. Along with their editing duties, Sommerfeld and Langevin
shared for several years the electromagnetic world-view, which
promised a unification of all forces on an electromagnetic basis. But
as mentioned above, in late 1908, theory and experiment conspired to
convince Langevin of the cogency of the theory of relativity.

As a former student of Poincaré’s, and an occasional dinner guest at
his flat in Paris, Langevin would have been at first glance a natural
candidate to take up Poincaré’s theory of relativity. A similar remark
may be made about Sommerfeld, who did not hear Poincaré’s lectures at
the Sorbonne, but who admired and emulated his approach to
physics. Whatever affinity Sommerfeld and Langevin had with Poincaré
and his science, they both preferred the Einstein-Minkowski theory to
that of Poincaré. For Sommerfeld, it was Minkowski’s spacetime theory
that persuaded him of the cogency of relativity
theory.^{48}^{48}Walter 1999, 70. Langevin, too,
was impressed by Minkowski’s theory, and by Sommerfeld’s related
four-dimensional vector algebra and analysis, which he presented in
his 1910–1911 lectures at the Collège de France.^{49}^{49}Sommerfeld
1910a,
1910b.
Likewise, Minkowski admired
Langevin’s contributions to the kinetic theory of gases; see
Minkowski to Felix Klein, 1 Oct. 1906, Klein Nachlass,
Niedersächsische Staats- und Universitätsbibliothek. The elements of spacetime theory
were readily available to French readers by then, since in late 1909,
a pair of former students of the *École normale supérieure* had
translated Minkowski’s 1908 lecture ‘‘Space and time’’ for publication
in the *Annales scientifiques de l’École normale
supérieure*.^{50}^{50}Minkowski (1909), translated
from the German original by Aimé Hennequin and Joseph Marty. On
Poincaré’s response to Minkowski’s theory, see Walter
(2009).

Like Poincaré, Langevin felt that the ether was not a wholly superfluous concept for modern physics. One auditor of Langevin’s lectures, Léon Brillouin, recorded Langevin’s remark on this subject:

The very notion of the ether loses its sense, says Einstein – this is an exaggeration. We can’t discern our speed with respect to the ether, but we can discern [our] accelerations and rotations.

^{51}^{51}‘‘La notion même d’éther perd son sens, dit Einstein–c’est exagéré. On ne peut saisir notre vitesse p[ar] rapp[ort] à l’éther, mais on peut saisir les accélérations et rotations.’’ Léon Brillouin, Notebook ‘‘Cours de Relativité au Collège de France 1910–1911’’, Léon Brillouin Papers, Box 7, folder 8, American Institute of Physics, Niels Bohr Library. Langevin made the same point – without mentioning Einstein by name – in a lecture delivered on 10 April 1911 to the Fourth International Congress of Philosophy in Bologna, where Poincaré was present; see Langevin (1911, 233).

On the subject of light-waves, Langevin maintained on another occasion
that a spherical light-wave in one inertial frame is actually spherical
for all inertial observers.^{52}^{52}Langevin
1912, 335. The latter view signals Langevin’s
break with Poincaré, for whom the light locus only *appeared*
spherical for observers in motion with respect to the ether. In fact,
Langevin fully agreed with Einstein and Minkowski that the universal
validity of the principle of relativity implied a new view of space
and time, and he defended this view publicly, beginning in 1911.

To put Langevin’s defense of Einstein-Minkowski theory into historical
perspective, let us examine some publication numbers. In 1911,
publication of articles on relativity theory in periodicals worldwide
hit a peak at one hundred and seventeen titles, after a sustained
increase in scientific interest beginning in 1909 (see Fig. 1). This
increase is reflected on a modest scale, and with a delay of a year or
two, in the United Kingdom and in France. Figure 2 shows the evolution of
publication numbers from 1905 to 1916 for the top five nations in
article productivity. French numbers rose slightly in 1911, and peaked
at thirteen articles in 1913.^{53}^{53}These publication
numbers do not take into account an author’s nationality or
workplace. Data correlating the production of articles on
relativity to nationality of the writer is presented in Walter
(1996), which is also the source of the data in the
figures presented here, augmented by fifty titles gleaned from the
author’s subsequent research. The publication database is freely
available from the author’s
homepage.

Bare publication numbers tell us nothing of the causes of their annual
fluctuation, a fact which leads us back to the *JPTA* abstracts. In
1911, ‘‘Einstein theory’’ is mentioned in nine abstracts, six of which
mention no other theory. Next comes ‘‘Lorentz theory’’, with five
mentions, followed by one mention each for Poincaré and Minkowski. The
novelty in 1911 French physics, according to this source, was
Einstein’s theory of relativity.
A closer look at the *JPTA* abstracts, however, suggests that
these citation figures be treated with prudence. In 1911, the *JPTA*
recruited a new abstract writer, a nautical engineer from Antibes,
Maurice Lémeray (b. 1860), and assigned him articles on relativity
published in German or English. A science teacher turned warship
designer, Lémeray was himself a prolific writer on relativity,
having published more articles in 1911 and 1912 than any other
Frenchman. His writings show no marked allegiance to either Einstein or Poincaré,
but agree in general with Einstein’s theory. Indeed, Lémeray was the first to
cite Einstein’s publications on relativity in the *Comptes
rendus*, in a note communicated to Academy of Sciences by Poincaré,
whose name Lémeray was careful to cite.^{54}^{54}Lémeray
1911. In summary, the increased number of
citations of Einstein’s theory in the 1911 *JPTA* abstracts has
more to do with staff changes at the *JPTA* than with any bound
in recognition of Einstein’s contributions to relativity among French
physicists.

The details of Lémeray’s rise to prominence in France throw light on
the reception of Einstein’s theory. Archival documents reveal that
Lémeray sought the Paris Academy’s approval for his work on relativity
as early as September 1910, when he submitted a manuscript to Gaston
Darboux, one of the Academy’s permanent secretaries.^{55}^{55}Session
folder, 3 October 1910, Archives of the Academy of Sciences, Paris.
Judged unfit for publication, the four-page note entitled ‘‘On the
Lorentz transformation’’ purported to demonstrate Lorentz’s formulas
for local time, length contraction, and transverse and longitudinal
mass from Einstein’s twin postulates of relativity and universal
lightspeed invariance, and dimensional analysis. Lémeray insisted that
his results were free of ‘‘any hypothesis on the mechanism of
phenomena or on any electrical theory’’, and he cited only one paper:
Einstein’s first French-language publication on relativity in the
*Archives de Genève*. His purported demonstration of time
dilation from the longitudinal Doppler effect for lightwaves, however,
involved circular reasoning, and probably rendered his manuscript
unpublishable. What this episode suggests is that the invisibility of
Einstein’s theory in France until 1911 was due in part to the paucity
of physicists prepared to meet the cognitive challenge of Einstein’s
theory, combined with the existence of a rigorous manuscript review
process. Similar instances of manuscript rejection in this area of
physics took place elsewhere, of course, Germany
included.^{56}^{56}See, for example, Lewis Pyenson’s review
(1985, chap. 8)
of Max Planck’s rejection of papers
submitted to the *Annalen der Physik*.

With assistance from Perrin, Langevin, and Lémeray, Einstein’s star
was ascending over France by 1911. In November, 1911, Poincaré
recommended him for a chair in theoretical physics at the ETH in
Zurich, commenting that ‘‘the future will show more and more what
Mr. Einstein’s value is’’, and in January 1912, Einstein was named to this
chair, and elected a non-resident council member of the French Society
of Physics.^{57}^{57}Poincaré to Pierre Weiss, ca. November, 1911,
transcribed in Walter et al., eds, 2007,
§ 59.3;
*Procès-verbaux de la société française de physique* 1912,
p. 9. In May, 1912, Poincaré admitted that the new
mechanics of relativity could serve as a basis for a redefinition of
time and space, thereby recognizing the philosophical significance of
Einstein-Minkowski theory.^{58}^{58}Poincaré
1912;
Walter 2009. This was a giant step for Poincaré,
but it came too late to make any difference for physics in France. By
1912, the leading French theorists, including Langevin, and the
mathematicians Émile Borel and Élie Cartan, had already adopted
Einstein-Minkowski theory.^{59}^{59}See Borel’s 1913 lectures on
Minkowski spacetime at the Sorbonne (Borel 1914), and
Cartan’s lecture on the ‘‘new kinematics’’ of relativity before the
French Society of Mathematics (Cartan 1912).

The engagement of Borel, Cartan, and other French mathematicians with the theory of relativity followed an example set in Germany by Minkowski, Gustav Herglotz, and Felix Klein. To some extent, the contributions of French mathematicians compensated the feeble participation of French theoretical physicists – Poincaré excepted – in the construction and diffusion of relativity. Once again, Langevin appears to have been instrumental in attracting the attention of French mathematicians to the study of Einstein-Minkowski theory. His role in introducing Einstein’s theory to French scientists was later described by Jacques Hadamard as follows:

It is well known that, under the powerful leadership of Mr. Langevin, the young French physicists rallied to the new movement of ideas created by Mr. Einstein’s discoveries. But cooperation with this movement was no less important to mathematicians, whose doctrines the new theory brought into play to a higher degree than any other previous physical conception. This is just what geometers like Mr. Borel understood from the beginning. (Hadamard 1922, i)

What Hadamard’s remark suggests is that for us to understand the reception of relativity in France, we need to go beyond the small circle of theoretical physicists, and examine how mathematicians came to engage with the theory.

In this essay, Poincaré’s influence on theoretical physicists in France has been discussed, but not his interaction with mathematicians. Nonetheless, even in the restricted domain of theoretical physics in France, the interactions between mathematics and physics appear decisive for the reception of relativity theory. The systematic appeal to sophisticated and powerful mathematics in the construction and elaboration of physical theory was a legacy Poincaré bestowed on all his physics students. In this sense, Poincaré may be said to have smoothed the path in France for both Paul Langevin and the Einstein-Minkowski theory of relativity, at the expense of his own approach to relativity.

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