Ann. Phys. (Berlin) 525, No. 8–9, A129–A133 (2013) / DOI 10.1002/andp.201300732
J. J. Thomson’s plum-pudding atomic model: The making of a
scientific myth
Giora Hon and Bernard R. Goldstein
was generally accepted as the best
available atomic theory.2 What distinguishes Thomson’s theory is his
assignment of a specific inner structure to the atom as well as a set of dynamical assumptions.
In 1899, in a paper addressed to
the British Association for the Advancement of Science, Thomson introduced the essential ingredients of
his model without any mathematical
formulas:
Figure 1 Joseph J. Thomson giving a lecture demonstration in the
1890s (Photo: courtesy of Niels Bohr Archive, Copenhagen).
Why “plum pudding”?
Joseph J. Thomson (1856–1940) was
one of the leading physicists at the
turn of the last century. In 1906
he was awarded the Nobel Prize in
physics for discovering the electron
and for his work on the conduction
of electricity in gases. Thomson’s discoveries raised questions concerning the nature of the atom. He
demonstrated that the atom is not
the simplest unit of matter; rather,
it has a structure. Thomson’s atomic
theory has informally been called
the “plum-pudding” model, but the
early history of this expression has
not been elucidated. The expression
is not in Thomson [1], the seminal
paper in which Thomson developed
his atomic theory, nor is it in any
of his subsequent publications. Although the historian Heilbron [2, 3]
has argued persuasively that this ex-
pression misrepresents Thomson’s
theory, it is still mentioned in respectable professional texts (sometimes labeled “inappropriate”): see,
e.g., [4–8]. As evidence for its occurrence in popular accounts, we
found that a Google search for “plum
pudding atomic model” yields over
100,000 hits. In other words, the expression is a commonplace and, as
we show, it is not simply an artifact
of recent popularization. So, what
were the circumstances that led to
calling Thomson’s theory the “plumpudding” model?
Thomson’s atom model and
its impact
As Kragh1 has noted, between 1904
and about 1910 Thomson’s model
1 See [4], p. 20.
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I regard the atom as containing
a large number of smaller bodies which I will call corpuscles; . . . .
In the normal atom, this assemblage of corpuscles forms a system which is electrically neutral.
Though the individual corpuscles
behave like negative ions, yet when
they are assembled in a neutral
atom the negative effect is balanced by something which causes
the space through which the corpuscles are spread to act as if it
had a charge of positive electricity
equal in amount to the sum of the
negative charges on the corpuscles
[10], p. 565.
These are preliminary remarks
in which Thomson was exploring
possibilities: he posited something
which behaves as if it had a positive
charge. But Thomson was certain
about the overall system, namely,
2 For a brief account of contemporary alternative atomic theories with references to
the original papers, see [9].
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THEN & NOW
Physics Forum
G. Hon and B. R. Goldstein: J. J. Thomson’s plum-pudding atomic model: The making of a scientific myth
the atom is a spatial domain filled
with numerous negative corpuscles
whose total charge is neutralized
somehow by the spatial positive
electrification.3
In May 1903 Thomson gave a
series of lectures at Yale University
in which he discussed the consequences of recent advances in
physics, including his own substantial contributions, remarking that
“we must face the problem of the
constitution of the atom, and see if
we can imagine a model which has
in it the potentiality of explaining
the remarkable properties shown
by radio-active substances” [11].
Thomson then addressed the
question, how do the corpuscles
arrange themselves in a sphere?
He began by considering one
corpuscle and appealing to equilibrium as a guiding constraint [11]
(pp. 111–117). The resulting theory was based on “the atoms of
the chemical elements [which]
are built up of large numbers of
negatively electrified corpuscles
revolving around the centre of a
sphere filled with uniform positive
electrification” [12]. His conception
of the atom now included corpuscles whose motions take place in
orbits and, due to the forces exerted
on the orbits, each orbit “may be
constrained to occupy an invariable position with respect to the
aggregate—as if, to take a rough
analogy, the orbit was a tube bored
through the aggregate, so that the
orbit and the aggregate move like a
rigid body . . . ” [12] (p. 690). Although
Thomson appeals to “a rough analogy”, what he presents is an atomic
model. As far as we can determine,
in his subsequent publications
he invoked neither “analogy” nor
“aggregation”—an indication that
Thomson was groping for a way to
address atomic phenomena. Both
his methodology and terminology
were in transition.
A theory was then required to account for the atomic structure. The
full title of Thomson’s paper of 1904
is “On the structure of the atom: an
investigation of the stability and periods of oscillation of a number of
corpuscles arranged at equal intervals around the circumference of a
circle; with application of the results
to the theory of atomic structure.”
He began as follows:
The view that the atoms of the elements consist of a number of negatively electrified corpuscles enclosed in a sphere of uniform
positive electrification, suggests,
among other interesting mathematical problems, the one discussed in this paper, that of the
motion of a ring of n negatively
electrified particles placed inside a
uniformly electrified sphere [1].
3 Cf. [4] p. 8.
Thomson constructed his atomic
theory so that it would be conducive
to mathematical analysis where stability, as the title indicates, plays
a critical role. The atom in equilibrium has n corpuscles and they
are arranged at equal angular intervals on rings inside a positively
electrified sphere, each corpuscle
carrying a charge of negative electricity. The task was then to find
a stable structure which comprises
corpuscles bearing negative electric
charges (i.e., electrons) immersed in
a sphere of positive electrification to
render the atom electrically neutral
and yet capable of giving an account
of its chemical properties. In Thomson’s view his calculations showed
that the proposed structure does indeed account for the chemical properties of the atom [1] p.258.
In 1907 Thomson published a
book, The corpuscular theory of matter, based on a course of lectures
he had given at the Royal Institution
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in the spring of 1906. In these lectures Thomson discussed the theory
of the constitution of matter which,
for Thomson, supposes that the various properties of matter may be
regarded as arising from electrical
effects. The later chapters of Thomson’s book contain
a discussion of the properties of
an atom built up of corpuscles and
of positive electricity, the positive
electricity being supposed to occupy a much larger volume than
the corpuscles . . . . I think that a
theory which enables us to picture
a kind of model atom and to interpret chemical and physics results
in terms of such model may be
useful even though the models are
crude . . . [13] p. v-vi.
For Thomson the model served
as a heuristic device exhibiting two
principal features, namely, the stability and unity of atomic phenomena, both chemical and electrical.
Thomson’s theory was part of the
background for the various atomic
theories that replaced his model,
notably those of Ernest Rutherford
(1871–1937) [14] and Niels Bohr
(1885–1962) [15]. In particular, Bohr
was very much influenced by the
work of his mentors, Thomson and
Rutherford, whom he cited extensively throughout his Trilogy of 1913,
in which he introduced the quantum
theory of the atom.
In his address to the British Association for the Advancement of Science, August 18, 1914, Rutherford
took stock of the current state of the
theory of the atom:
The idea that the atom is an electrical structure received a great impetus by the detection of the electron
by J. J. Thomson . . . . In J. J. Thomson’s model of the atom the positive electricity was supposed (for
mathematical reasons) to be distributed throughout a large sphere
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Ann. Phys. (Berlin) 525, No. 8–9 (2013)
Physics Forum
with the negative corpuscles moving inside it. This hypothesis has
played a useful part in indicating
possible lines of advance; but it
does not fit in with more recent discoveries, which point to a concentrated positive nucleus [16].
Rutherford was well positioned
to assess Thomson’s contribution
and he noted that, while Thomson’s
model was not consistent with newly
found experimental results of deflections of particles, his theory “played
a useful part” in pointing to fruitful
lines of research. One such line was
taken up by Bohr in his construction
of the quantum theory of the atom in
1913.
Bohr described Thomson’s theory and went on to claim that the
configurations allowed in Thomson’s
atom-model “apparently do not exist for the second [i.e., Rutherford’s]
atom-model” [15] (p. 2). As is well
known, in his quantum theory of the
atom Bohr took as his point of departure the atomic structure which
Rutherford had proposed and explicitly discarded that of Thomson,
inaugurating a new era in physics exactly 100 years ago.4
The “plum pudding” in
popularizations
Merck’s Report was a practical journal of pharmacy as a profession and
a business. In an essay published in
December 1906, the question “What
is matter?” was addressed, in which
a report was given on a series of
lectures delivered by Thomson earlier in 1906:
4 For a detailed analysis of Bohr’s contribution to atomic physics in 1913 in the context of the work of his predecessors (including Thomson) see, e.g., [4, 17]. An
upcoming contribution to this section
by Martin Jähnert will deal with Bohr’s
theory.
Figure 2 A plum pudding (Source: http://www.thatslife.com.au,
photo: Richard Whitbread).
The most favored theory [for the
constitution of matter] of the
present time is that which Prof.
J. J. Thomson . . . has expounded
. . . at the Royal Institution . . . in
a series of lectures entitled the
“Corpuscular Theory of Matter.”
The lectures were delivered . . .
in March and April [1906], and
these notes . . . are the gist of what
our representative gathered from
lecture to lecture [18].
Here we find, as far as we can
tell, the first occurrence in print of
the expression “plum pudding” with
respect to Thomson’s theory.5 The
anonymous representative who attended Thomson’s series of lectures
reported among other things that
Professor Thomson suggests [that]
. . . while the negative electricity
is concentrated on the extremely
small corpuscle, the positive electricity is distributed throughout
a considerable volume. An atom
would thus consist of minute
specks, the negative corpuscles,
swimming about in a sphere of
positive electrification, like raisins
in a parsimonious plum pudding,
units of negative electricity being
5 For an earlier unsuccessful attempt to locate the first occurrence of “plum pudding” as a characterization of Thomson’s
model, see [19] pp. 148–149, 291.
C 2013 by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.ann-phys.org
attracted toward the center, while
at the same time repelling each
other [18].
Now a plum pudding is a suet
pudding with raisins, traditionally served at Christmas. Despite
its name, this pudding contains
raisins rather than plums. Clearly,
the anonymous reporter knows his
pudding: he describes the plum
pudding correctly. But there is
no correspondence between the
embedded raisins and the revolving corpuscles for, according to
Thomson’s theory of 1906, the
electrons revolve on rings about
the center of the atom, and they
are not distributed throughout the
“pudding” as “raisins swimming
about”. Merck’s report tells us that
the plum-pudding image was originally based on a misunderstanding
of Thomson’s theory.
We have also found the expression “like plums in a pudding” in
an anonymous report of a discussion that took place on August 2,
1907 as part of the annual meeting
of the British Association in Leicester, England [20]. The relevant passage reads:
Whether [the atom] consists of a
central body surrounded by a ring
of electrons, or whether the electrons are immersed in the central
body, like plums in a pudding, are
alternatives of which anyone may,
at present, take his choice, for the
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G. Hon and B. R. Goldstein: J. J. Thomson’s plum-pudding atomic model: The making of a scientific myth
truth is that the materials are not
sufficient for a decision [21].
The invocation of “plum pudding” (here without naming Thomson) is misleading in two respects,
namely, the plums in fact are raisins
and, more importantly, it is misleading, as we have seen, to liken Thomson’s model to a plum pudding.6
The making of a myth
On all accounts plum pudding is
a curious image for the atom, and
one wonders what could have been
the source for these anonymous
reporters. One possibility is that
they depended on a passage in
the physics textbook, Properties of
matter (1885) by P. G. Tait (1831–
1901), which includes, inter alia, a
survey of several hypotheses concerning the ultimate structure of
matter.7 Against the limitations of
two conceptions, the discrete hard
atom on the one hand, and continuous mathematical points on the
other, Tait presents what he considers a more plausible theory: “Matter is continuous (i.e. not made up
of particles situated at a distance
from one another) and compressible, but intensely heterogeneous;
like a plum-pudding, for instance,
or a mass of brick-work” [23]. Tait’s
plum-pudding image was offered as
an attempt to reconcile the continuous with the discrete; this was a
problem of accommodation within
the classical domain. The imagery
6 A detailed report on this meeting appeared in [22]. There is no “plum pudding”
in this “official” account.
7 Tait’s Properties of matter appeared in four
editions in his lifetime (1885, 1890, 1894,
and 1899) and a fifth edition appeared in
1907, all of which are indications of its
popularity.
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is designed to depict matter in general; the atom did not yet have a
structure.
Given these historical data, we
notice a curious fact, namely, a
misleading popular image entered
scientific and scholarly discussions.
As we have seen, physicists like
Rutherford and Bohr who responded
professionally to Thomson’s model
atom conceived it in his own terms
and did not present any pictures
or introduce any analogies to facilitate comprehension. Indeed, there
was no need for such imagery.
However, contemporary popularizers, who sought to make the emerging modern physics accessible to the
general public, wished to avoid technical aspects of the theory, offering
instead a vivid image. It is unfortunately a frequent occurrence that
popularizations misrepresent scientific theories; however, what is surprising in the “plum-pudding” case,
is the fact that the scholarly literature adopted this misleading characterization of Thomson’s model atom.
At the outset Thomson considered
the atom a structural unity within
which numerous negatively charged
corpuscles transverse a positively
charged space. The model changed
over the years, eventually becoming
a positively electrified space within
which relatively few electrons set on
rings circulate about a mathematical center. The scene is energetic,
clearly dynamical, and nowhere are
raisins/plums stuck in a pudding.
Acknowledgment. One of us [GH] is grateful to the Alexander von Humboldt Foundation for its support.
Giora Hon
Department of Philosophy
University of Haifa
Haifa 31905, Israel
E-mail: hon@research.haifa.ac.il
Bernard R. Goldstein
Dietrich School of Arts and Sciences
www.ann-phys.org
University of Pittsburgh
Pittsburgh, PA 15260, USA
E-mail: brg@pitt.edu
References
[1]
[2]
[3]
[4]
[5]
[6]
[7]
[8]
[9]
[10]
[11]
[12]
[13]
[14]
[15]
[16]
J. J. Thomson, Phil. Mag. 7, 237
(1904).
J. L. Heilbron, Lectures on the
history of atomic physics 1900–
1922, in C. Weiner, ed., History
of twentieth century physics
(Academic Press, New York and
London, 1977), p. 52, 54.
J. L. Heilbron, Nature 498, 27
(June 6, 2013).
H. Kragh, Niels Bohr and the
quantum atom: The Bohr model
of atomic structure 1913–1925
(University Press, Oxford, 2012),
p. 8, 17.
M. J. Nye, From chemical philosophy to theoretical chemistry
(University of California Press,
Berkeley, 1993), p. 133.
J. Navarro, Hist. Sci. 44, 470
(2006).
O. Bueno and S. French, Brit. J.
Phil. Sci. 62, 873 (2011).
H. De Cruz, and J. De Smedt,
Phil. Stud. 157, 421 (2012).
http://skullsinthestars.com/2008/
05/27/the-gallery-of-failedatomic-models-1903–1913/.
J. J. Thomson, Phil. Mag. 48, 547
(1899).
J. J. Thomson, Electricity and
matter (Yale University Press,
New Haven, 1904), p. 92.
J. J. Thomson, Phil. Mag. 36, 673
(1903).
J. J. Thomson, The corpuscular
theory of matter (Archibald Constable, London, 1907).
E. Rutherford, Phil. Mag. 21, 669
(1911).
N. Bohr, Phil. Mag. 26 1 [I], 476
[II], and 854 [III] (1913).
E. Rutherford, Discussion of
the structure of atoms and
molecules, in Report of the
eighty-fourth meeting of the
British Association, Australia,
July 28 – August 31, 1914 (John
Murray, London, 1915), p. 293.
C 2013 by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Ann. Phys. (Berlin) 525, No. 8–9 (2013)
J. L. Heilbron, Phys. Today, 30, 23
(1977).
[18] Anonymous, Merck’s Report, 15,
359 (December 1906).
[19] A. A. Martı́nez, Science Secrets
(University of Pittsburgh Press,
Pittsburgh 2011).
[20]
C 2013 by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
E. Rutherford, Discussion on the
constitution of the atom. Report
of the Seventy-Seventh Meeting
of the British Association for the
Advancement of Science, Leicester, 31 July–7 August 1907 (John
Murray, London, 1908), p. 439.
www.ann-phys.org
[21]
Anonymous,
The
Outlook
(London), 20, 176 (August 10,
1907).
[22] Anonymous, Nature 76, 457
(August 29, 1907).
[23] P. G. Tait, Properties of matter
(Black, Edinburgh, 1885), p. 19.
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Physics Forum
[17]