resisting the bohr atom: the early british...

Resisting the Bohr Atom: The Early BritishOpposition

Helge Kragh*

When Niels Bohr’s theory of atomic structure appeared in the summer and fall of 1913, itquickly attracted attention among British physicists. While some of the attention was sup-portive, others was critical. I consider the opposition to Bohr’s theory from 1913 to about1915, including attempts to construct atomic theories on a classical basis as alternatives toBohr’s. I give particular attention to the astrophysicist John W. Nicholson, who was Bohr’smost formidable and persistent opponent in the early years. Although in the long runNicholson’s objections were inconsequential, for a short period of time his atomic theorywas considered to be a serious rival to Bohr’s. Moreover, Nicholson’s theory is of interest inits own right.

Key words: Niels Bohr; Antonius van den Broek; Norman R. Campbell;

Arthur W. Conway; Albert C. Crehore; Evan J. Evans; Alfred Fowler;

William D. Harkins; William M. Hicks; James H. Jeans; Joseph Larmor; Frederick

A. Lindemann; Thomas R. Merton; Henry G.J. Moseley; John W. Nicholson;

William Peddie; Edward C. Pickering; John S. Plaskett; J.J. Thomson; Owen W.

Richardson; Ernest Rutherford; Johannes R. Rydberg; Frederick Soddy; Arnold

Sommerfeld; Ernest D. Wilson; British Association; Bohr atom; spectroscopy;

atomic number; atomic structure; astrophysics; history of atomic physics;

history of quantum physics.

Introduction

The quantum atomic model that Niels Henrik David Bohr (figure 1) introduced in

1913 marked a new and eminently fruitful chapter in the history of atomic theory,

eventually leading to the modern quantum–mechanical atom. While the history of

Bohr’s atom is well understood, only relatively little historical research has been

devoted to its reception in different countries and scientific communities.1 I

examine the early reception principally in England, focusing on critical voices

rather than those speaking in favor of the new theory.

* Helge Kragh is Professor of History of Science at the University of Aarhus, Denmark. Hismain research interests are in post-1850 developments of physics, chemistry, and cosmology.

Phys. Perspect. 13 (2011) 4–35� 2010 Springer Basel AG

1422-6944/11/030004-32

DOI 10.1007/s00016-010-0048-z Physics in Perspective

4

As to the latter, I should note that very few British physicists (if any) accepted

Bohr’s theory in toto, including the two quantum postulates that constituted the

conceptual basis of his theory. It was more common to use the theory eclectically,

to accept parts of it while ignoring or rejecting other parts. At times the distinction

between proponents and opponents could be difficult to tell. Moreover, some of

those who disliked Bohr’s theory did not oppose it in public but chose to express

their dissatisfaction by ignoring it.

The Reception of Bohr’s Theory

Niels Bohr’s pathbreaking quantum theory of atomic structure appeared in a

sequel of three papers in the Philosophical Magazine under the common title, ‘‘On

the Constitution of Atoms and Molecules.’’2 The first part of the trilogy was

published in the July 1913 issue, the second part in September and the third part in

November. Two years later, Bohr’s theory was widely accepted or at least seri-

ously considered by physicists working with quantum theory and the structure of

matter. Given the radical nature of the assumptions on which the theory rested—

the frequency postulate and the postulate of stationary electron orbits—Bohr

could be satisfied with how it was received by leading physicists in England and

Germany. Of course, its victory was not complete, for many physicists resisted it

and even more were indifferent or just ignorant of it. Yet, by the end of 1915

the majority of physicists doing research in atomic physics and related areas

Fig. 1. Niels Bohr (1885–1962). Credit: Courtesy of Niels Bohr Archve.

Vol. 13 (2011) Resisting the Bohr Atom 5

recognized that Bohr’s theory constituted an important advance that might well

define the course of future research.

Bohr’s atomic model attracted interest among English physicists at an earlier

date than among their colleagues in Germany. This was in a sense natural. After

all, Bohr stayed in England for most of the period between 1912 and 1916, and

his theory appeared in a leading British journal. It relied on and was closely

related to works of British physicists, in particular Ernest Rutherford, Alfred

Fowler, Charles Glover Barkla, and Henry Gwynn Jeffries Moseley. Moreover,

the style of Bohr’s theory was British, closely connected as it was to the tra-

dition of British atom builders. Although Bohr’s atom replaced the classical

electron atom of Joseph John Thomson and can in some sense be seen as a

revolt against this kind of atom, historian John L. Heilbron has argued that

‘‘Bohr’s atomic theory belongs to the program of semiliteral model making

initiated by J.J. Thomson and based on the methods of mid-Victorian Cam-

bridge physics.’’3

At the 1913 meeting of the British Association for the Advancement of Science,

which took place in Birmingham from September 10–17, James Hopwood Jeans

introduced a discussion session on problems of radiation theory. Discussants

included such luminaries as Hendrik Antoon Lorentz and Joseph Larmor, and also

Bohr, who had come from Copenhagen to participate in the meeting. Jeans had

only recently become sympathetic to the quantum theory. Two years earlier, at the

first Solvay Congress, he had attempted to account for Planck’s constant of action

h on classical grounds, but at the Birmingham meeting he tentatively suggested a

dynamical interpretation of the quantity, namely,

h ffi 2pð4peÞ2

c;

where e is the elementary charge and c the velocity of light. In terms of the later

fine-structure constant a his expression can be written as 1/a = 16p2 % 158.

Jeans’s interpretation of h went contrary to Bohr’s thinking, for according to Bohr

Planck’s constant was an irreducible constant of nature that could not be explained

in terms of other constants.

Whatever the differences in opinion, in Birmingham Jeans gave a concise

account of Bohr’s ‘‘most ingenious and suggestive, and I think we must add con-

vincing, explanation of the laws of spectral series.’’4 Although Jeans found Bohr’s

theory convincing, he was less happy with its foundation in Bohr’s two quantum

postulates. ‘‘The only justification at present put forward for these assumptions is

the very weighty one of success,’’5 he said. It might be the only justification, but

according to Jeans and several of his colleagues it was enough to take the theory

seriously. Bohr later recalled that Jeans’s ‘‘lucid exposition was, in fact, the first

public expression of serious interest in considerations [of my theory] which outside

the Manchester group were generally received with much scepticism.’’6

6 H. Kragh Phys. Perspect.

In his influential report on radiation and quantum theory that appeared the

following year, Jeans spoke even more positively, and in greater detail, about

Bohr’s theory. The new quantum theory of atoms, as exposed in the ‘‘very

remarkable and intensely interesting Papers [sic] by Dr. Bohr, of Copenhagen,’’

appeared prominently in Jeans’s report. As he phrased it, Bohr’s fundamental

assumption ‘‘is not inconsistent with the quantum-theory and is closely related to

it.’’7 Although he expressed some reservation with respect to the applicability of

Bohr’s theory to more complex atoms, he praised it for having opened a rich field

by the use of quantum theory to problems of atomic structure.

Few British physicists realized how drastically Bohr’s theory departed from

conventional physics, for example, that it denied the applicability of the principles

of mechanics to systems of atomic dimensions. And most of those who did

opposed the theory precisely for this reason. Norman Robert Campbell, a former

student of J.J. Thomson at the Cavendish Laboratory, recognized more clearly

than most the radical nature of Bohr’s atomic model. ‘‘To attempt to explain

Bohr’s theory in terms of those principles [of classical physics] is useless,’’ he

pointed out in a review of January 1914. Campbell praised the assumptions of

Bohr’s theory, which he saw as ‘‘simple, plausible, and easily amenable to math-

ematical treatment; from them all the properties of any atomic system which does

not contain more than one electron can be deduced uniquely.’’8 As to more

complex atomic systems, Campbell admitted that the power of the theory was

limited, but instead of regarding that as a serious flaw he thought it was ‘‘owing to

the mathematical difficulties involved.’’

As a third example of the positive reception of Bohr’s theory, consider Owen

Willans Richardson, another former student of J.J. Thomson at the Cavendish

Laboratory, who in 1906 was appointed Professor of Physics at Princeton Uni-

versity. A specialist in electron theory and the emission of electrons from hot

bodies—in 1928 he would receive the Nobel Prize for his work in this area—he was

acquainted with Bohr’s theory of atomic structure at an early time. He knew it not

only from Bohr’s papers in the Philosophical Magazine but also from a conver-

sation he had with Bohr in Cambridge in July 1913, just when Bohr’s theory

appeared.9 In a book of 1914 on electron theory based on a series of lectures given

at Princeton, The Electron Theory of Matter,10 Richardson included Bohr’s new

atomic theory, although in much less detail than he gave to the classical Thomson

model.11 His book was positively reviewed by Bohr in Nature.12

Richardson’s Electron Theory of Matter was probably the earliest treatment of

Bohr’s theory in a regular textbook, but it was not the first book that referred to it.

George W.C. Kaye, a physicist at the National Physical Laboratory in Teddington,

on the outskirts of London, and a former collaborator of J.J. Thomson, published

in early 1914 a book on X rays and their uses in which he included two references

to Bohr’s theory. Relegating Thomson’s atomic theory to a footnote, he adopted

the Bohr–Rutherford model according to which, ‘‘The outer electrons, by their

number and arrangement, are responsible for the chemical and physical properties


of the atom: the inner electrons have influence only on the phenomena of

radioactivity.’’13

To return to Richardson, he was clearly impressed by the agreement of Bohr’s

theory with spectra. Noting that although Bohr’s theory ‘‘frankly discards

dynamical principles,’’ he considered it nonetheless to be successful and very

promising. There is no doubt, he said, ‘‘that this theory has been much more

successful in accounting quantitatively for the numerical relationships between the

frequencies of spectral lines than any other method of attack which has yet been

tried.’’14 Moreover:

Although the assumptions conflict with dynamical ideas they are of a very

simple and elementary character. The fact that they conflict with dynamics does

not appear to be a valid objection to them, as there are a number of other

phenomena, the temperature radiation for example, which show that dynamics

is inadequate as a basis for a complete explanation of atomic behaviour.15

In the second edition of 1916, whose preface he signed on January 11, 1916, he

dealt in much more detail with Bohr’s theory,16 if still presenting it as merely an

alternative to the Thomson model. Richardson rated the theory highly and dealt in

considerable detail not only with the hydrogen atom, but also with many-electron

atoms, the H2 molecule, and X-ray spectra. Yet he also covered J.J. Thomson’s

earlier theory in even greater detail, being careful to avoid confronting the two

theories. Having presented them, he left it to the reader to decide between the

two. Although Richardson clearly valued Bohr’s theory, apparently he did not

fully realize its nonclassical features and its disagreement with the classical elec-

tron theory on which most of his book was based.17

The positive responses of physicists like Jeans, Campbell, and Richardson,

however, were not representative of the early reception in England. Others found

Bohr’s theory attractive mainly for experimental reasons, and especially because

of its successful explanation of spectra, while still others were sceptical or opposed

to it. I shall focus on the latter, who can be divided into two groups: those who

implicitly expressed their dislike by ignoring the theory, and those who criticized it

in public. But I first need to sketch a topic that played an important role in the

reception of Bohr’s theory among British physicists.

The Pickering-Fowler Spectral Series

According to Bohr’s theory (figure 2), all frequencies of the hydrogen spectrum

can be written as

m ¼ R1

n22

� 1

n21

� �with R ¼ 2p2me4

h3:

Here n1 and n2 are integers, n1 [ n2; m and e denote the mass and numerical

charge of the electron. In the case of a one-electron system heavier than hydrogen,


such as He? and Li??, Rydberg’s constant R would have to be replaced with Z2R,

where Z is the charge of the nucleus (Z = 1 for hydrogen). Even before the

publication of the first part of his trilogy, Bohr was aware that certain lines nor-

mally ascribed to hydrogen did not fit his formula. These lines were found in stellar

spectra by the astronomer Edward Charles Pickering in 1896 and in discharge

tubes with a hydrogen–helium mixture by the astrophysicist Alfred Fowler in

1912.18 What appeared to be an anomaly was resolved by Bohr by assuming that

the lines were not due to hydrogen, but to singly ionized helium with Z = 2. In

that case he could rewrite the above formula as

m ¼ 4R1

n22

� 1

n21

� �¼ R

1

n2=2ð Þ2� 1

n1=2ð Þ2

!

and show that it accomodated the new spectral series of Pickering and Fowler.

Evan Jenkin Evans, a member of Rutherford’s group in Manchester, found the

same strong line of wavelength 4,686 A that Fowler had detected, but in pure

helium with no trace of hydrogen.19 He consequently interpreted it as a confir-

mation of Bohr’s theory, according to which the line was due to a quantum

transition in He? from n1 = 4 to n2 = 3. Unconvinced that Bohr had really

explained the 4,686 A line and other lines in the supposed hydrogen series, in the

fall of 1913 Fowler pointed out that the theoretical values did not quite agree with

Fig. 2. Bohr’s model of the hydrogen atom as depicted in early 1915 by William D. Harkins and

Ernest D. Willson. Source: Harkins and Wilson, ‘‘Structure of the Atom’’ (ref. 99), p. 1406.


the observed ones.20 Bohr’s response was to modify his analysis by taking into

account the finite mass of the nucleus by replacing m with the reduced mass

l ¼ m

1þm=M;

where M is the mass of the nucleus. This modification resulted in much better

agreement, which made Fowler concede that Bohr’s theory gave a correct

explanation.21 ‘‘For me the origin of the 4686 & Pickering series is no longer ‘a

vexed question’,’’ he wrote to Bohr. ‘‘Your theory has the great merit of

accounting for the lines in positions slightly different from those calculated by

Rydberg, and of predicting Evans’s lines.’’ Fowler’s support, however, was not

unqualified. He ended his letter: ‘‘But perhaps we may find that some other theory

will do the same thing. Meanwhile I am a warm supporter of your theory.’’22

In October 1913 Bohr had argued that if his theory of Fowler’s lines were

correct, one should also expect a series of He? lines very close to the ordinary

hydrogen Balmer spectrum. The lines would correspond to transitions from

n1 = 6, 8, 10, … to n2 = 4. Experiments conducted by Evans in late 1914 con-

firmed the series predicted by Bohr, which was one more triumph of the new

atomic theory.23

Thomson’s Silence

J.J. Thomson (figure 3), a pioneer of electron and atomic physics, was by 1913 still

considered to be a recognized authority in atomic structure, and his ideas were

taken very seriously, especially in Britain. His earlier ‘‘plum-pudding model’’ of the

atom, which he had presented in quantitative detail in 1904 and which in some

respects inspired Bohr, was for a brief period of time the best offer of a theory of

atomic structure.24 However, at the time of Rutherford’s announcement of the

atomic nucleus in 1911 it had been abandoned by Thomson himself and most other

physicists, if not yet replaced by Rutherford’s alternative conception of the atom.

Resisting quantum theory as well as the nuclear model, Thomson proposed a

new model of the atom that had few similarities with his old one. He presented it

to the British Association in September 1913 and in even greater detail to the

Solvay Congress the following month.25 A main feature of Thomson’s new model

was that the atom consisted of a radial repulsive force that varied inversely as the

cube of the distance from the center of the atom and was diffused throughout the

atom, and a radial attractive force that varied inversely with the square of the

distance from the center of the atom and was confined to a limited number of

radial tubes in the atom. Making use of these and other assumptions, Thomson

succeeded, to his own satisfaction, to reproduce Einstein’s equation for the pho-

toelectric effect,26 including Planck’s constant h, which he characteristically

expressed in terms of atomic constants. He arrived at the expression h ¼ pffiffiffiffiffiffiffiffiffiffiCemp

;

where C is a force constant numerically adjusted to give the correct value of


h. He also showed that his model provided an explanation of the production of

X rays and some of the data known from X-ray spectroscopy. Moreover, he and

others applied his model to throw light on the nature of valency and other

chemical phenomena, which for a time made his model popular among chemists.

Although Thomson’s model of 1913 was very different from Bohr’s, the two

models addressed many of the same problems and therefore were, in a sense, rival

conceptions of atomic structure. For example, Thomson found electron configu-

rations for the simpler atoms that corresponded to the known periodicity of the

elements,27 much like Bohr had done in the second part of his trilogy. It thus

seems surprising that Thomson simply chose to ignore Bohr’s theory; he did not

mention it in any of his works of 1913 or the following years. Increasingly isolated

from mainstream physics, he consistently kept to his classical picture of the atom,

modifying it from time to time in ways that were conspicuously ad hoc. Only in

1919 did he confront Bohr’s atom, which by this time enjoyed general acceptance

among experts in atomic and quantum theory.

Thomson’s objections to the quantum atom in 1919 were methodological rather

than technical and presumably reflected those he had when he first read Bohr’s

papers. Referring to Bohr’s principle of discrete orbits or energy states charac-

terized by quantum conditions, he wrote:

This, however, is not the consequence of dynamical considerations; it is arith-

metical rather than dynamical, and if it is true it must be the result of the action

Fig. 3. Joseph John Thomson (1856–1940). Credit: Burndy Library Collection, Huntington

Library; courtesy of American Institute of Physics Emilio Segre Visual Archives.


of forces whose existence has not been demonstrated. The investigation of such

forces would be a problem of the highest interest and importance. By the use of

this principle and a further one, that when an electron passes from one orbit to

another it gives out radiation whose frequency is proportional to the difference

of the energy of the electron in the two orbits, Mr. Bohr obtains an expression

which gives with quite remarkable accuracy the frequencies of the lines in the

four-line spectrum of hydrogen. It is, I think, however, not unfair to say that to

many minds the arithmetical basis of the theory seems much more satisfactory

than the physical.28

Thomson further objected, as others had, that, ‘‘The vibrations which give rise to

the spectrum do not on this theory correspond in frequency with any rotation or

vibration in the atom when in the steady and normal state.’’ According to

Thomson there was convincing experimental evidence, especially based on

absorption spectra, that an electron in an unexcited state of the atom vibrates with

the frequencies of its spectral lines. In short, as he saw it, Bohr’s quantum atom

was a mathematical construct with no basis in established physics. He kept to this

view throughout his life, although eventually admitting that Bohr’s theory had ‘‘in

some departments of spectroscopy changed chaos into order.’’29

Bohr was not impressed by Thomson’s new model of the atom, but he realized

that it could be seen as an alternative to his own and therefore contemplated a

response. A month after the meeting of the British Association, and after

Thomson’s paper had been published in the Philosophical Magazine, he wrote to

Rutherford on October 16, 1913: ‘‘As to the theory of the structure of atoms of Sir

J.J. Thomson, I did not realise in Birmingham how similar many of his results are

to those I had obtained,’’ adding that ‘‘this agreement has no foundation in the

special atom-model used by Thomson but will follow from any theory which

considers electrons and nuclei and makes use of Planck’s relation E = hm.’’30 Bohr

drafted a letter, apparently meant for Nature, in which he said about the same

thing, but did not send it.31 In his letter to Rutherford he elaborated his objections

to Thomson’s model as follows:

Thus—quite apart from the fact that the assumption of repulsive forces varying

inversely as the third power of the distance is in most striking disagreement with

experiments on scattering of a–rays,—Thomson finds a value for the funda-

mental frequency of the hydrogen-atom which is 4 times too small, and a value

for the ionization-potential of the hydrogen atom which is about half that

experimentally found by himself. Besides Thomson’s theory apparently gives

no indication of an explanation of the laws of the line-spectra, and—making the

atom a mechanical system—offers no possibility of evading the well-known

difficulties of black[body]-radiation and of specific heat.32

Rutherford expressed himself less diplomatically, at least in private. In a letter to

the American radiochemist Bertram Borden Boltwood he characterized the


Thomson atom as ‘‘only fitted for a museum of scientific curiosities.’’33 To Arthur

Schuster, then Secretary of the Royal Society, he wrote: ‘‘I believe he [Thomson]

knows in his heart that his own atom is not worth a damn and will not do the things

it has got to do.’’34 No conflict arose between Bohr and Thomson; each largely

cultivated his own line of work without bothering too much about the other’s

theory. Bohr was confident that Thomson’s theory belonged to the past, while his

own belonged to the future.

Another of the highly respected physics professors of the old guard, Joseph

Larmor, since 1903 Lucasian Professor of Mathematics at the University of

Cambridge, also chose to ignore the Bohr atom. A celebrated pioneer of electron

theory, Larmor had dealt extensively with atomic theory in his Wilde Lecture of

1908,35 but when the theories of Rutherford and Bohr appeared he remained

silent. Only in 1929, in a postscript to a paper of 1921 on nonradiating atoms, did

he briefly refer to the Rutherford-Bohr model of the atom.36 The Third Lord

Rayleigh (John William Strutt) had contributed to the early phase of quantum

theory, but he too never responded to Bohr’s theory of the atom. His son and

biographer, the Fourth Lord Rayleigh (Robert John Strutt), said that he asked his

father in 1913 if he had seen Bohr’s paper on the hydrogen atom, who replied,

‘‘Yes, I have looked at it, but I saw it was no use to me. I do not say that discoveries

may not be made in that sort of way. I think very likely they may be. But it does

not suit me.’’37

Classical Alternatives to the Bohr Model

The British atom-building tradition in the style of Thomson did not collapse

overnight with the advent of Bohr’s new model of atomic structure. It continued

for some years, in most cases with the atom builders devising models that incor-

porated limited features of quantum theory, as in the works of Thomson and John

W. Nicholson (see below). Some of these classical models referred to and were

inspired by Bohr’s theory, or were critical responses to it. They were all short-

lived. Only a few physicists, notably Nicholson and Frederick A. Lindemann,

campaigned actively against Bohr and his supporters.

Arthur William Conway (figure 4), Professor of Mathematical Physics at Uni-

versity College, Dublin, had done important work in theoretical spectroscopy and

also had worked on mathematical formulations of electrodynamics and special

relativity theory. In December 1913 he proposed an atomic model based on

classical mechanics and electromagnetism with the aim of explaining—or rather

illustrating—some of the properties of spectral series.38 ‘‘The atom considered is a

‘Thomson’ [plum-pudding] atom rotating with a constant angular velocity,’’ he

wrote, which he modified in such a way that the positive sphere was capable of

executing elastic vibrations. He found that (his italics) ‘‘in every steady motion the

angular momentum of the negative electron has the same constant value,’’ which he

identified with h/p, or twice that obtained by Bohr. Conway’s h was not really


Planck’s constant but a quantity he deduced from spectroscopy, and his atomic

model just happened to yield a value of h very close to Planck’s quantum of action.

His attempt to clarify the connection between Bohr’s theory and his own—‘‘two

theories so very different from one another’’—was unconvincing and revealed a

lack of understanding of the meaning of Bohr’s atomic theory.39 In a note of 1914

Conway argued that his model, if supplied with certain assumptions, was able to

reproduce Fowler’s spectrum and thus provided an alternative to Bohr’s expla-

nation.40 The implication was that Bohr’s atom was not necessary.

Two months later, again in the pages of the Philosophical Magazine, another

and more elaborate atomic theory was proposed, this time by William Peddie

(figure 5), Professor of Physics at University College in Dundee.41 A former

assistant of Peter Guthrie Tait, Peddie worked mainly in color theory, dynamics,

and molecular magnetism. The atomic model he introduced in 1914 was a

‘‘spherical counterpart of the tubular atom of Sir J.J. Thomson,’’ consisting of a

series of negatively charged shells surrounding a positive core and constructed in

such a way as to give the desired results. After many calculations Peddie managed

to obtain from his model Balmer’s spectral formula, account for the law of

photoelectricity, and come up with a qualitative explanation of radioactivity. His

general idea was to derive optical and other phenomena from ‘‘a complicated

structure of the atom itself’’—and Peddie’s spherical atom was indeed compli-

cated. Bohr had deduced his results in a ‘‘beautifully direct manner,’’ but

unfortunately in a way that could not be reconciled with the known laws of

Fig. 4. Arthur William Conway (1875–1950). Source: Whittaker, ‘‘Conway’’ (ref. 38), facing page

329.


dynamics and electromagnetism. As Peddie saw it, for this reason the Bohr atom

could not be a model of the real constitution of atoms. He spelled out his critique

as follows:

The value of the new ideas [of Bohr] as a working hypothesis cannot be denied.

But behind all this procedure there lies the root question whether or not the

peculiarities, so readily explained on the new ideas, cannot be explained in

terms of the ideas of the older physics as consequences of structural

conditions.42

Peddie thought this could be done: ‘‘it does not seem to me that we are yet under

compulsion to forsake the laws of ordinary dynamics in connexion with atomic

properties, or the doctrine of a continuous wave-front in æther, or even, apart from

magnetic action, the notion of central symmetry in atomic motion.’’43

As a third and last example of a classical alternative to the Bohr atom, consider

a work by the American physicist and inventor Albert Cushing Crehore (figure 6),

a former Assistant Professor of Physics and Electrical Engineering at Dartmouth

College.44 Immediately following Bohr’s first paper in the July 1913 issue of the

Philosophical Magazine there appeared a long 60-page (!) paper by Crehore on

atomic and molecular structure.45 Crehore adopted Thomson’s classical plum-

pudding model, which he developed in different ways and extended into an

elaborate theory of molecules, crystals, and more. It is informative to compare

Crehore’s model with Bohr’s—two theories dealing with the same subject matter,

the structure of atoms and molecules, and yet very different in both substance and

method. By February 1915 Crehore had modified the Thomson model into a

Fig. 5. William Peddie (1861–1946). Source: website \http://www-history.mcs.st-and.ac.uk/

Mathematicians/Peddie.html[.


http://www-history.mcs.st-and.ac.uk/Mathematicians/Peddie.html

http://www-history.mcs.st-and.ac.uk/Mathematicians/Peddie.html

‘‘corpuscular-ring gyroscopic theory,’’46 in part in an attempt to introduce Planck’s

constant and take into account the works of Bohr and Henry G.J. Moseley. His

theory included electron configurations of the elements in the periodic system

(figure 7).

Noting that, ‘‘The present tendency among atomic theorists is to favour with

Rutherford an atom with a central positive nucleus having electrons circulating in

orbits,’’47 Crehore devised a theory that eclectically included features of both the

Thomson model and the Bohr-Rutherford model. In what he thought was in

agreement with Bohr, he assumed, on the one hand, that undisturbed electrons

describing circular orbits did not emit radiation. On the other hand, while on the

Bohr-Rutherford model beta particles had their origin in the nucleus, in Crehore’s

theory they might arise from the emission of any electron in the atom. The

American physicist used his speculative theory to offer an alternative explanation

of X-ray spectra, to account for photoelectricity, to suggest the existence of

positive electrons, and to predict an upper limit of atomic weight corresponding to

the weight of uranium. In another paper of 1915 he extended his atomic specu-

lations to the molecular realm, including the hypothetical H3 molecule and more

complicated molecules of organic chemistry.48

But borrowing a few features of Bohr’s theory did not make Crehore accept

Bohr’s theory: ‘‘Although Bohr has in a brilliant manner given an explanation of

some of the series of spectral lines, notably those of H and He, yet it may fairly be

said that luminous spectra have not been explained by any atomic theory.’’49 As

evidence he cited Nicholson, who had ‘‘shown in a seemingly conclusive manner

that these spectra are not really accounted for on Bohr’s hypothesis.’’ Crehore

Fig. 6. Albert Cushing Crehore (1868–1959) ca. 1910. Source: Crehore, Autobiography (ref. 44),

p. 88.


continued to construct electromagnetically-based atomic models that avoided the

unpalatable quantum jumps. In one of these works he summed up his and other

conservative physicists’ dissatisfaction with the Bohr atom: ‘‘The Bohr model

affords no picture of anything that really vibrates with the observed frequencies,

since nothing is said about the model during the very time when the radiation is

taking place, but merely about its state before and after such radiation.’’50

Although Crehore’s works were ignored by most physicists, they were serious

attempts to establish a theory of atomic structure on the basis of electrodynamics

without denying Bohr’s postulate of nonradiating stationary orbits.

John Nicholson, Atom Builder

At the meeting of the British Association held in 1914 in Melbourne, Australia,

Bohr’s theory was discussed in a joint meeting of Section A (mathematics and

physics) and Section B (chemistry). While Rutherford did not mention Bohr’s

ideas, they were critically addressed by William Mitchison Hicks (figure 8) and

John W. Nicholson. Hicks, who had studied under Maxwell and in 1883 advanced

to a professorship at Firth College in Sheffield, had been a leading advocate of the

vortex theory of atoms, a research program that in a general sense continued to

appeal to him (as it did to J.J. Thomson).51 His view of atomic theory may be

illustrated by his praise of Conway’s recent and ‘‘most suggestive’’ paper offering

an electrodynamic explanation of the origin of spectra. ‘‘We want more of a similar

Fig. 7. A part of Crehore’s periodic system of 1915, with electron configurations of the atoms.

Crehore adopted Rydberg’s ordinal number, implying two elements between hydrogen and

helium. The number of electrons in the rings is indicated by the numbers in the lower left-hand

corner of the squares. The Rydberg ordinals, two units higher than van den Broek’s atomic

numbers, are given in the lower right-hand corner. The element of ordinal number 6 is beryllium,

then sometimes known by its older name ‘‘glucinium,’’ symbol Gl. Source: Crehore, ‘‘Gyroscopic

Theory’’ ref. (46), p. 323.


nature,’’ he said.52 That Hicks was not in the vantguard of physics is further

illustrated by his dismissal of the Bohr-Rutherford picture of helium as the ele-

ment of atomic number 2. He argued that its atomic number was more probably 4,

implying the existence of at least one unknown element between hydrogen and

helium.

From the point of view of the Bohr-Rutherford theory, intermediary elements

were impossible, but this was nonetheless what the recognized Swedish spectros-

copist Johannes Robert (‘‘Janne’’) Rydberg held. He was followed by a few other

scientists, including Hicks, Nicholson, Crehore, and the Swiss chemist Alfred

Werner. Rydberg argued that the ordinals of elements were two units greater than

the atomic numbers adopted by Bohr and Moseley.53 Thus, in the first period there

should be four elements rather than just hydrogen and helium, lithium should be

element number 5, and so forth. In his periodic system of 1913, he included the

hypothetical ‘‘coronium’’ and ‘‘nebulium’’ among the light elements (figure 9).

Recall that by 1914 the concept of atomic number was new and far from

obvious. The idea that all chemical elements can be characterized uniquely by a

serial number (rather than an atomic weight) had been in the air for a couple of

years and was accepted by Rutherford and his group in Manchester. According to

Charles Galton Darwin, ‘‘the whole Manchester laboratory believed in the

undoubted existence of atomic number, defined as the nuclear charge.’’54 The

hypothesis was first explicitly proposed by the Dutch lawyer and amateur physicist

Fig. 8. William Mitchison Hicks (1850–1934). Credit: American Institute of Physics Emilio Segre

Visual Archives, W.F. Meggers Collection.


Antonius van den Broek in a paper of 1913.55 He recognized that the serial

number was equal to the intra-atomic or nuclear charge. The notion of atomic

number—the name was coined by Rutherford—was quickly adopted by Bohr,

Moseley, Frederick Soddy, and some other leading scientists, but it took several

years before van den Broek’s hypothesis won general recognition. Chemists, in

particular, were slow to adopt the idea, which implied a redefinition of chemical

elements.

Admitting that Planck’s constant had a role to play in atomic theory, Hicks

discussed the theory of Bohr—or ‘‘Bohr’’ as he spelled it in the proceedings of the

British Association—which he praised as ‘‘most ingenious and suggestive.’’56

However, ingenious and suggestive as it was, he dismissed it on both methodo-

logical and empirical grounds. As to the latter, he objected that Bohr’s theory was

valid for hydrogen only and thus not really a theory of atoms and spectra.

Although his theory had ‘‘caught the scientific imagination,’’ it failed to offer a true

explanation, meaning a mechanism for the emission of light. ‘‘It is based on the

Rutherford atom, but throws no further light on the structure of the atom itself, as

Fig. 9. Part of Rydberg’s periodic system of 1913, covering the elements from hydrogen to

iodine. Note the two elements between hydrogen and helium, which Rydberg thought was

nebulium (number 2) and coronium (number 3). Also note the element designated as 0, which he

identified with the electron. Source: J.R. Rydberg, ‘‘Untersuchungen uber das System der

Grundstoffe,’’ Lunds Universitets Arsskrift Ny Foljd 9, No. 18 (1913), p. 23.


the mechanism of radiation is totally unexplained, and it is this which we are in

search of.’’ Hicks had more confidence in the rival atomic theory of Nicholson,

which he thought was generally correct and ‘‘stands alone as a first satisfactory

theory of one type of spectra.’’

Bohr could afford to ignore the alternatives and objections of scientists like

Conway, Peddie, Hicks, and Crehore, whose ideas were so clearly out of tune with

mainstream physics. The opposition of Nicholson was a different matter, however,

for not only had Nicholson proposed a kind of quantum atomic model before

Bohr, his views also enjoyed considerable respect among British physicists and

astronomers. For example, Jeans’s report on radiation and quanta of 1914 included

not only an account of Bohr’s theory of the structure of atoms but also one of

Nicholson’s theory, about which Jeans concluded that ‘‘it has probably already

succeeded in paving the way for the ultimate explanation of the phenomenon of

the line spectrum.’’57 Only in the case of Nicholson did Bohr become involved in

something that was close to a controversy over atomic structure.

John William Nicholson (figure 10) was lecturer in the Cavendish Laboratory

until 1912, when he was appointed Professor of Mathematics in the University of

London, King’s College. Before turning to astrophysics and atomic theory, his

main work was in the mathematical theory of electromagnetic waves. In 1911—the

same year that Rutherford’s nuclear atom saw the light of day—he proposed that

atoms consisted of a tiny center of positive electricity around which electrons

revolved in rings.58 His ideas of atomic constitution derived from astrophysics

rather than laboratory physics and chemistry, in which respect they differed from

those of Bohr and most other physicists. In agreement with the earlier views of his

compatriots William Crookes and Joseph Norman Lockyer, he was convinced that

terrestrial matter had evolved from simpler forms that still existed in the heavens

Fig. 10. John William Nicholson (1881–1955). Source: Wilson, ‘‘Nicholson,’’ ref. (58), facing

p. 209.


and could be studied by means of the spectroscope. To understand the architecture

of atoms, physicists would have to look to the heavenly regions.

In a visionary paper of early 1913, Nicholson argued forcefully that astrophysics

was ‘‘an arbiter of the destinies of ultimate physical theories.’’59 He made clear that

the simple model atoms deduced, for example, from the coronal spectrum were

very different from the more complex atoms found on Earth. ‘‘[When] an astro-

physicist discovers hydrogen in a spectrum, he is dealing with hydrogen in a

simpler or more primordial form than any known to a terrestrial observer.’’ He

therefore found it useless to test his atomic theory with terrestrial substances.

‘‘[The] most satisfactory test of the newer physical theories,’’ he wrote, ‘‘is to be

derived from a discussion of the accumulated results of astrophysical

observation.’’60

The atomic model proposed by Nicholson was mainly concerned with four

primary elements that were supposed to exist in the nebulae and the Sun’s corona.

The simplest of these elements was ‘‘coronium’’ with two electrons revolving on a

ring around a nucleus of positive charge 2e. He found the atomic weight of cor-

onium to be 0.513. Nicholson’s other primary elements were ‘‘hydrogen,’’

‘‘nebulium,’’ and ‘‘protofluorine,’’ with three, four, and five electrons on the same

ring, respectively, and of atomic weights 1.008, 1.628, and 2.362. Although Nich-

olson’s three-electron ‘‘hydrogen’’ was closely related to the chemical element

hydrogen, he did not conceive the two to be identical. In his original scheme

coronium was the simplest possible atomic system.

In 1914 Nicholson extended his list of primary elements, now including

‘‘protohydrogen’’ with a single electron revolving around a positive unit charge,

and ‘‘archonium’’ with a nucleus of positive charge 6e. He assumed that ordinary

hydrogen was an evolution product of protohydrogen, but with a nucleus of a

more complicated structure, consisting of x ‘‘positive electrons’’ and (x - 1)

negative electrons. In general, Nicholson stressed the difference between his

celestial primary elements and those found on Earth, a difference he ascribed in

part to the complex nature of the atomic nucleus. ‘‘[The] nuclei in terrestrial

atoms are not simple,’’ he wrote in 1914, ‘‘they consist of a complicated system

of positive and negative charges closely packed together, and not a mere

positive charge.’’61 Nicholson saw his belief in what he called ‘‘sub-elements’’

(and what Lockyer had called ‘‘protoelements’’) vindicated by astrospectroscopic

measurements. For example, he found the mass of archonium to be 2.945 and

calculated that the doubly charged positive archonium ion should radiate with a

wavelength of 3,729 A. When Charles Fabry and his colleagues Henri Bourget

and Henri Buisson detected a double line of wavelength 3,726–3,729 A in the

Orion nebula and attributed it to an unknown gas of atomic weight approxi-

mately 3, Nicholson naturally concluded that the existence of archonium had

now been confirmed.62 He denied the possibility that the line could be due to

the H3 molecule recently discovered by J.J. Thomson in experiments with

positive rays.


Although Nicholson’s calculations of the spectra of hypothetical elements had

an air of numerology, his theory resulted in impressive agreement with spectro-

scopic measurements and several successful predictions. More importantly, in his

attempts to explain the line spectra and determine the dimensions of the primary

atoms, he was led in 1912 to introduce Planck’s constant into his theory.63 Up to

this time Planck’s quantum of action had always been associated with energy, in

the form E = hm. Nicholson now concluded that the angular momentum L of

simple atoms could only change by integral multiples of the quantity h/2p, that is,

L ¼ nh

2p; n ¼ 1; 2; 3; . . .

William Wilson, Nicholson’s colleague at King’s College, London, later recalled

that his own discovery of what is sometimes known as the Wilson-Sommerfeld

quantum conditions was inspired by Nicholson’s work on angular momentum.64

Moreover, in his critical analysis of Bohr’s atomic model, Nicholson recognized

that the orbits of the electrons might be elliptical rather than circular. He imagined

a system of n electrons describing a set of equally spaced ellipses, with the nucleus

at their common focus. The electrons, he explained in 1914, ‘‘are at the corners of a

regular polyhedron inscribed in a circle.’’65 Four years later, an arrangement of this

kind was adapted by Arnold Sommerfeld in what he called an Ellipsenverein

(figure 11), a concept that for a time played an important role in the old quantum

theory. Sommerfeld acknowledged that the idea had originally come from Nich-

olson.66 While there were some similarities between Nicholson’s atomic theory

and the one proposed by Bohr in 1913, the two theories differed profoundly. While

Nicholson’s theory presupposed the applicability of classical mechanics and elec-

trodynamics, Bohr’s approach severely restricted such applicability and replaced it

by nonclassical assumptions. First and foremost, there were no quantum jumps in

Nicholson’s atoms. According to his theory, the spectral frequencies were vibra-

tion frequencies of the electrons in their circular orbits.

Bohr had first met Nicholson in Cambridge in late 1911, when both were

interested in the electron theory of metals. Nicholson had written a paper on the

subject that Bohr found to be ‘‘perfectly crazy,’’ as he wrote in a letter to his

Swedish friend Carl Wilhelm Oseen. ‘‘I have also had a discussion with Nicholson;

he was extremely kind, but with him I shall hardly be able to agree about very

much.’’67 At that time Bohr was unaware of Nicholson’s atomic theory, which he

first referred to in a postcard about a year later, where he suggested that Nich-

olson’s ideas of the structure of atoms were not incompatible with his own ideas.68

This is also what he said to Rutherford in a letter of late January 1913, at a time

when he had not yet connected his atomic theory to spectra. Bohr considered

Nicholson’s theory to stand in a complementary rather than contradictory rela-

tionship to his own: while Bohr’s theory dealt with the permanent state of atoms,

Nicholson’s atoms were unstable and ‘‘only present in sensible amount in places in

which atoms are continually broken up and formed again, i.e. in places such as


excited vacuum tubes or stellar nebulae.’’69 Two months later, after having

extended his atomic theory into a theory of spectra, Bohr argued that the spectral

lines considered by Nicholson were due to a scattering of radiation, while his own

theory dealt with its emission. If so, ‘‘Nicholson’s theory would fit exceedingly well

in with the considerations of my paper.’’70

In the first part of his trilogy, Bohr referred extensively to Nicholson’s theory,

but at the same time he was eager to distance his own model from it but not to

present the two theories as irreconcilable alternatives. Repeating what he had

suggested to Rutherford, he argued that the objections to Nicholson’s theory

might be ‘‘only formal’’ because the proper domain of his theory was scattering

rather than emission of radiation. From that point of view it was understandable

that Nicholson’s theory, contrary to his own, was unable to account for the spectral

regularities of Balmer and Rydberg. In spite of his reconciliatory tone, Bohr

emphasized that his new quantum theory of atoms rested on an entirely different

basis than the one adopted by Nicholson: ‘‘In Nicholson’s calculations the fre-

quency of lines in a line-spectrum is identified with the frequency of vibration of a

mechanical system in a distinctly indicated state of equilibrium.’’71 In Bohr’s

theory, the frequencies arose from nonmechanical quantum transitions.

Nicholson versus Bohr: Objections and Responses

Nicholson first responded to Bohr’s theory in a letter to Nature of October 16,

1913, in which he briefly discussed Bohr’s quantization rule L = nh/2p for many-

electron atoms in relation to his own. He argued that the two rules gave different

results for all atomic systems except one-electron atoms. Although Nicholson was

generally positive, he was not all that impressed by Bohr’s theory and its recent

Fig. 11. The figure on the left shows Nicholson’s illustration of two electrons moving

synchronously in ellipses. Source: Nicholson, ‘‘High-Frequency Spectra’’ (ref. 65), p. 557. The

figure on the right is Sommerfeld’s five-ellipse Ellipsenverein, which was a generalization of

Nicholson’s picture. Source: Sommerfeld, Atombau und Spektrallinien (ref. 66), p. 367.


success in explaining the Pickering-Fowler lines as due to the He? ion. ‘‘The real

test of his theory will lie in its capacity to account for the usual spectrum of

helium,’’72 he wrote, thus agreeing with the evaluation recently stated by Alfred

Fowler. Nicholson repeated his criticism at the British Association meeting in

Melbourne, where he said that in order to go further than hydrogen, ‘‘we must

abandon at least one of Bohr’s premises which is vital to the deduction of the

hydrogen formula.’’73 Nicholson’s letter in Nature was just an overture for the

much more extensive critique that, recognizing the threat from Bohr’s rival theory

of atoms, he soon launched in a series of papers.

Nicholson’s primary aim was not to defend his own model, but rather to

demonstrate irreparable weaknesses in Bohr’s theory by examining it from Bohr’s

own premises, or what he thought was Bohr’s premises. Contrary to most other

critics, Nicholson had a deep knowledge of Bohr’s atomic theory, which he

examined in great technical detail, often greater than Bohr himself had consid-

ered. His judgment of Bohr’s theory wavered somewhat, but was basically critical.

At times he indicated that his own theory and Bohr’s were not necessarily in

conflict and might perhaps both be valid descriptions—complementary in some

sense. ‘‘[The] two theories give the same constitution for the atom of hydrogen,’’

he claimed in 1914, ‘‘except that the dynamical one [Nicholson’s] is somewhat

more specific.’’74 On this occasion Nicholson suggested that both theories might be

correct, Bohr’s relating only to terrestrial atoms and his own only to simple one-

ring systems of the kind found in the heavens.

Rather than going through all of Nicholson’s many critical comments and

arguments, I shall only mention some of his main objections. I group these in four

classes:

1. Emission of X rays. According to Nicholson’s analysis, two or more coplanar

rings of electrons could not exist, neither on his dynamical theory nor on

Bohr’s theory. Mechanical stability required that either the electrons must

move in different planes, or they must all lie on the same circle. This implied

that Bohr’s explanation of Moseley’s results for X rays was necessarily

incorrect. Calling Bohr’s theory ‘‘so attractive that its retention is desirable,’’

Nicholson nonetheless concluded that ‘‘we must give up the idea of concentric

rings in the atom, with X-radiation coming from an inner ring.’’75 In another

paper of 1914 he concluded that ‘‘Moseley’s observations have shown no

relation to Bohr’s theory.’’76 Bohr, of course, disagreed, and so did Moseley.

While Nicholson dismissed the Bohr-Moseley explanation of X-ray spectra, he

proposed that a one-ring modification of Bohr’s theory might explain the

emission of X rays. However, in that case one would have to abandon the

notion of atomic number as the ordinal number of the periodic system, a

notion that was crucial to Bohr’s and Moseley’s theories.

2. Atomic number. A recurrent theme in Nicholson’s criticism was that ‘‘van den

Broek’s hypothesis’’ of the atomic number was in conflict with Bohr’s theory.


Since Bohr’s theory for atoms more complex than helium was founded on the

notion that the nuclear charge was the ordinal number for the periodic system,

this was a serious charge. ‘‘If we are to retain Bohr’s theory of such complex

atoms,’’ Nicholson wrote, ‘‘that theory must give up van den Broek’s

hypothesis in its present form.’’77 Van den Broek himself responded to

Nicholson’s arguments, which he thought were ill founded: ‘‘generally

speaking, Bohr’s theory is not in disagreement with the atomic number

hypothesis.’’78 Nicholson was willing to accept some version of the atomic-

number hypothesis, but not that the atomic number defined the place of an

element in the periodic system and limited the number of elements in a period.

He considered the periodic system less important for atomic theories than

astrophysical evidence. That evidence demanded the existence of several

elements lighter than helium, and according to the atomic-number hypothesis

there was no room for these elements.

3. Lithium atom. Since Nicholson had concluded that Bohr atoms could only

have a single ring, Bohr’s (2,1) configuration of lithium, as presented in the

second part of his trilogy, had to be wrong: ‘‘[It] is not possible for three

electrons and a nucleus to form a lithium atom with a unit valency, after the

manner of Bohr’s model.’’79 He argued further that Bohr’s theory of valency

and the structure of complex atoms led to results that were grossly inconsistent

with chemical knowledge. For example, lithium should be an inert element,

carbon a monovalent element of metallic nature, and nitrogen a divalent

metal. So much for Bohr’s chemistry! In early 1913 Nicholson had suggested

that unidentified lines in the spectra of certain stars (Wolf-Rayet stars) were

due to a new hydrogen series whose frequencies m were given by

m ¼ R1

4� 1

n� 13

� �2

!:

However, Bohr had argued in his trilogy that Nicholson was mistaken, and

that the spectral lines were probably due to doubly ionized lithium (Z = 3),

just as the Pickering-Fowler spectral lines had their origin in ionized helium.80

He simply rewrote Nicholson’a expression as m = 9R(1/62 - 1/x2). But as

Nicholson saw it, it was Bohr who was mistaken. Bohr’s reinterpretation of the

stellar lines depended on a model of the lithium atom that was dynamically

impossible.

4. Hydrogen and helium. Bohr’s theory was singularly successful when applied to

the simplest elements, hydrogen and ionized helium, but according to

Nicholson Bohr’s success was only partially deserved. He concluded from

detailed analyses that except for the neutral hydrogen atom Bohr’s model

failed even for simple systems such as He?, H2, He, and H-. Nicholson

admitted that ‘‘the theory is definitely successful when there is only one

electron,—and also, at the same time, when there is only one nucleus,’’ but for


all other atomic and molecular systems ‘‘it rests on a slender foundation.’’81

Even in the case of the neutral hydrogen atom it failed to deliver a complete

solution. Nicholson summarized: ‘‘Bohr’s theory cannot explain any portion of

the hydrogen spectrum except the Balmer and Ritz series, and perhaps a

Schumann [ultraviolet] series. It also predicts some strong series which are not

found.’’82 Of what worth was an atomic theory that was valid, or merely

partially valid, only for a single element? Bohr’s theory, he wrote, must ‘‘stand

or fall according to its capacity to take account more completely of the spectra

of these two elements,’’ namely hydrogen and helium. Especially with regard

to helium he was convinced that Bohr’s theory failed to live up to its promises.

Having investigated various ways to generalize and modify the theory so as to

explain the helium spectra, ‘‘we must conclude that it cannot develop in the

manner which its earlier success appeared to foreshadow.’’83 At the

Melbourne meeting of the British Association he concluded similarly, namely,

that ‘‘the balance of experimental evidence is against Bohr’s theory at

present.’’84

Some of Nicholson’s objections to Bohr’s theory, and especially as they related toX-ray spectroscopy, were independently argued by Frederick Alexander Linde-mann, later Viscount Cherwell. While the general view was that Moseley’s dataprovided strong support for Bohr’s theory, Lindemann argued that this was not thecase, and that the data merely supported the hypothesis of atomic number assuggested by van den Broek, Rutherford, and others. ‘‘The agreement of Bohr’sconstant with experimental data is not convincing to my mind in view of the largenumber of arbitrary assumptions in his derivation.’’85 By means of elaboratedimensional analyses he suggested that there were many ways in which resultsequivalent to Bohr’s could be obtained, including some that avoided reference toquantum theory. Lindemann denied that experiments, whether in the X-ray oroptical region, provided unambiguous support for ‘‘Dr. Bohr’s special assump-tions.’’ Bohr immediately penned a brief reply in which he criticized the procedureadopted by Lindemann, and Moseley also responded, repeating that his exper-iments did confirm Bohr’s theory.86

The objections Nicholson raised were a more serious matter, and Bohr

intended to reply to them. He drafted a letter to Nature,87 and a longer one to

the Philosophical Magazine, but he mailed neither of them. Although ‘‘I admit

most readily the importance of the difficulties discussed by Prof. Nicholson,’’ he

wrote in the longer draft reply, ‘‘I cannot, on the other hand, feel convinced that

the basis for his calculations is sufficiently self-contained to justify his conclu-

sions.’’88 Bohr’s published replies came in the form of two papers in 1915, the

first on the hydrogen and helium spectra, the second on a general development

of his theory of atoms and radiation. ‘‘I am unable to agree with Nicholson’s

conclusions,’’ he stated, apparently unwilling to face these conclusions in detail.89

He did however take care to repudiate Nicholson’s argument that the 4,686 A

line and the new series discovered by E.J. Evans were not evidence for Bohr’s


theory as they might well be due to hydrogen rather than ionized helium. In a

reply to Evans in early 1915, Nicholson maintained that the nature of the 4,686

A line was still a ‘‘vexed question.’’90 Bohr flatly disagreed, concluding that ‘‘at

present there is scarcely sufficient theoretical evidence to justify us in disre-

garding the direct evidence as to the chemical origin of the lines given by

Evans’s experiments.’’91

There might be no ‘‘theoretical evidence’’ to doubt that the 4,686 A line was due

to ionized helium, but at Imperial College doubts remained about the empirical

evidence. In a paper of March 1915 the spectroscopist Thomas Ralph Merton

observed that Bohr’s theory ‘‘has given rise to a considerable amount of theo-

retical discussion.’’92 Spectroscopic experiments based on a new interference

method suggested to him that the evidence provided by Evans was inconclusive

and that the mass of the atom from which the 4,686 A line originated was much

smaller than that of the helium atom. He found that it was only about one-tenth of

the mass of a hydrogen atom and thus was ‘‘due to systems of subatomic mass.’’

What these systems might be, Merton did not say. Nor did he spell out the the-

oretical significance of his conclusion, although it obviously contradicted Bohr’s

explanation.

It seems that Bohr (figure 12) convinced himself that it was not worth entering

into a dispute with Nicholson, whose premises and way of thinking differed too

much from his own to make it worthwhile. ‘‘His whole point of view is so foreign to

me,’’ he wrote to Oseen in September 1914, adding that ‘‘by a departure from

mechanics I understand something much more radical than he does.’’93 To Hans

Marius Hansen, his friend and colleague in Copenhagen, Bohr expressed himself

in a similar way: ‘‘You have probably seen quite a bit of criticism, which has

appeared; especially from Nicholson. I do not think it has any foundation. I feel

that Nicholson treats the question not as a physical, but as a purely literary one.’’94

He soon came to see the critique from Nicholson, Lindemann, and others as

insignificant and not worth worrying about. ‘‘I don’t think that any of it means

anything,’’ he wrote in a letter to his brother Harald.95 Not only did Bohr refrain

from entering a public discussion with Nicholson, he also did not communicate

with him privately. The extensive collection of Bohr’s correspondence from this

period on deposit at the Niels Bohr Archive in Copenhagen contains no letters to

or from Nicholson.

Nicholson’s arguments against Bohr’s atomic models relied in part on calcu-

lations that showed some of Bohr’s configurations to be mechanically unstable.

Unable to counter the mathematical arguments, Bohr decided that they were of

little importance because they presupposed that the motion of electrons could be

calculated on classical mechanics. Not all physicists ignored them with similar

ease. Stability calculations made by the German physicist Ludwig Foppl, a former

student of David Hilbert, confirmed some of Nicholson’s results that contradicted

Bohr’s models for atoms more complex than hydrogen.96 In his famous textbook


Atombau und Spektrallinien, Sommerfeld recognized the force of Nicholson’s

arguments in the case of the helium atom and other many-electron systems.97

Conclusions

Nicholson largely stopped criticizing Bohr’s theory after 1915, but he did not

change his view significantly on the structure of atoms and the existence of

celestial primary atoms. As late as 1919, in a lecture delivered to the Chemical

Society of London, he repeated his claims of the impossibility of coplanar rings of

electrons and the inconsistency between Bohr’s theory and X-ray spectra. Nor had

he softened his position with regard to Bohr’s model of the hydrogen atom which

he judged unsatisfactory because it only explained the Balmer spectrum and

similar line series. It failed to account for the more extensive spectrum of

hydrogen, including the so-called secondary spectrum that Nicholson thought was

due to atomic hydrogen. In spite of his innovative use of Planck’s constant,

Nicholson remained a classical physicist. For example, he spoke of the spectra as

‘‘dynamical vibrations of the atom, the frequencies of which are transmitted to our

instruments by the ether.’’98

In spite of the progressive development of Bohr’s theory, or what after 1915

became the Bohr-Sommerfeld theory, Nicholson’s alternative atomic theory was

not quickly forgotten. In a comprehensive review of recent theories of atomic

Fig. 12. Niels Bohr (1885–1962). Credit: Niels Bohr Archve; courtesy of American Institute of

Physics Emilio Segre Visual Archives.


structure, the American physical chemist William Draper Harkins at the Uni-

versity of Chicago and the English electrical engineer Ernest D. Wilson, a

colleague of Nicholson’s at King’s College, London, examined what they consid-

ered the two main alternatives, the theories of Bohr and Nicholson. They criticized

Bohr’s theory for being limited to one-electron atoms, but they praised Nichol-

son’s work because of its broad scope and ‘‘extreme interest to chemists.’’99 They

consequently covered Nicholson’s atomic theory in far greater detail than Bohr’s.

Nicholson’s work also appeared prominently in the series of annual progress

reports on radioactivity that Soddy wrote for the Chemical Society. In his progress

report of 1917 Soddy echoed Nicholson’s sceptical attitude to the Bohr atom: ‘‘In

spite of its great initial successes in calculating correctly the magnitude of the

Rydberg constant, and in correctly ascribing the Pickering series of lines to helium

rather than to hydrogen, Bohr’s theory does not seem to have been generally so

successful.’’100

Whereas Nicholson’s theory only aroused modest interest among physicists, its

astrophysical basis made it appealing among astronomers. In an address of 1915 to

the Royal Astronomical Society of Canada, John Stanley Plaskett, director of the

Dominion Astrophysical Observatory in Victoria, British Columbia, surveyed

Nicholson’s ‘‘very striking and beautiful theory of the evolution of the elements.’’

He found it to be more promising than Bohr’s atomic theory: ‘‘The question

between Nicholson and Bohr as to the constitution of the atom can not be

regarded as settled, however, although Nicholson appears to have the last

word.’’101 Still in 1920 his son, Harry Hemley Plaskett, dealt with Bohr’s and

Nicholson’s theories as if they were equally probable and fruitful.102

Yet, Nicholson’s atomic theory rested on the assumption of protoelements like

coronium and nebulium, and by the early 1920s belief in these and similar ele-

ments was rapidly in decline. Most astronomers and physicists expected that the

celestial spectral lines could be explained as arising from unusual states of ordinary

elements, which is what eventually happened. In 1927 the nebulium lines were

explained as transitions between metastable states in ionized oxygen and nitrogen

(O?, O??, N?); and in 1939 the coronium lines were shown to be due to highly

ionized iron (Fe13?).103 The chemistry of the heavens is exotic, but it does not

include protoelements outside the periodic system such as those imagined by

Nicholson.

By 1918 neither Nicholson’s nor others’ alternatives were seriously considered

by mainstream physicists. Tellingly, while Jeans had covered Nicholson’s theory in

his reports on quantum theory of 1914 and 1916, in later reviews he dealt exclu-

sively with the theory of Bohr and his school.104 After the Great War, the quantum

theory of atoms, based principally on the works of Bohr and Sommerfeld, stood

out as the only way to understand atoms and radiation. The continual scepticism in

some quarters of British physics, including scattered attempts to establish classical

alternatives, only meant that progress was now occurring elsewhere, first and

foremost in Germany.


Acknowledgments

I am grateful to the Niels Bohr Archive, Copenhagen, for granting me permission

to study Bohr’s letters and manuscripts from the period 1913-1915 and to

reproduce the picture of Bohr in figure 1. I also thank Roger H. Stuewer for

carefully editing my article and improving it in various ways.

References1 For a survey of the reception of the Bohr atom in England, Germany, and the United States, see

Helge Kragh, ‘‘The Early Reception of Bohr’s Atomic Theory (1913-1915). A Preliminary

Investigation,’’ RePoss: Research Publications on Science Studies 9, Department of Science

Studies, University of Aarhus. URL: http://www.ivs.au.dk/reposs.2 Niels Bohr, ‘‘On the Constitution of Atoms and Molecules,’’ Philosophical Magazine 26 (1913),

1-25; Part II. ‘‘Systems containing only a Single Nucleus,’’ ibid., 476-502; Part III. ‘‘Systems con-

taining Several Nuclei,’’ ibid., 857-875; reprinted in L. Rosenfeld, ed., Niels Bohr: On the

Constitution of Atoms and Molecules (Copenhagen: Munksgaard and New York: W.A. Benjamin,

1963), pp. 1-25, 28-54, 55-77; and Ulrich Hoyer, ed., Niels Bohr Collected Works. Vol. 2. Work on

Atomic Physics (1912-1917) (Amsterdam, New York, Oxford: North-Holland, 1981), pp. 161-185,

188-214, 215-233. Historical accounts include John L. Heilbron and Thomas S. Kuhn, ‘‘The

Genesis of the Bohr Atom,’’ Historical Studies in the Physical Sciences 1 (1969), 211-290; U.

Hoyer, Die Geschichte der Bohrschen Atomtheorie (Weinheim: Physik Verlag, 1974); J. L. Heil-

bron, ‘‘Rutherford-Bohr Atom,’’ American Journal of Physics 49 (1981), 222-231; Jagdish Mehra

and Helmut Rechenberg, The Historical Development of Quantum Theory. Vol. 1. Part 1. The

Quantum Theory of Planck, Einstein, Bohr and Sommerfeld: Its Foundation and the Rise of Its

Difficulties 1900-1925 (New York, Heidelberg, Berlin: Springer-Verlag, 1982), pp. 181-230; and

Abraham Pais, Niels Bohr’s Times, In Physics, Philosophy, and Polity (Oxford: Clarendon Press,

1991), pp. 132-159.3 Heilbron, ‘‘Rutherford-Bohr Atom’’ (ref. 2), p. 230.4 J.H. Jeans, ‘‘Discussion on Radiation,’’ Report of the Eighty-Third Meeting of the British Asso-

ciation for the Advancement of Science Birmingham 1913 (London: John Murray, 1914), pp. 376-

386, on p. 379.5 Ibid.6 Niels Bohr, ‘‘The Rutherford Memorial Lecture 1958: Reminiscences of the Founder of Nuclear

Science and of Some Developments Based on his Work,’’ Proceedings of the Physical Society 78

(1961), 1083-1115, on 1093; reprinted in David Favrholdt, ed., Niels Bohr Collected Works. Vol. 10.

Complementarity Beyond Physics (Amsterdam, Lausanne, New York, Oxford, Shannon, Singa-

pore, Tokyo: Elsevier, 1999), pp. 383-415, on p. 393.7 J.H. Jeans, Report on Radiation and the Quantum-Theory (London: ‘‘The Electrician,’’ 1914),

pp. 50, 51. He presented a similarly detailed review of Bohr’s theory in J.H. Jeans, The Dynamical

Theory of Gases, Second Edition (Cambridge: At the University Press, 1916), pp. 413-418; preface

dated January 1916.8 Norman Campbell, ‘‘The Structure of the Atom,’’ Nature 92 (1914), 586-587, on 587.9 Niels Bohr to Harald Bohr, July 30, 1913, in J. Rud Nielsen, ed., Niels Bohr Collected Works.

Vol. 1. Early Work (1905-1911) (Amsterdam: North-Holland and New York: American Elsevier,

1972), pp. 563-565, on p. 563.10 O.W. Richardson, The Electron Theory of Matter (Cambridge: At the University Press, 1914);

preface dated May 1914.


http://www.ivs.au.dk/reposs

11 Ibid., pp. 563-583, 585-587.12 N.B., [Review of O.W. Richardson, The Electron Theory of Matter], Nature 95 (1915), 420-421.13 G.W.C. Kaye, X-Rays: An Introduction to the Study of Rontgen Rays (London: Longmans,

Green and Co., 1914), p. 18; preface dated February 1914.14 Richardson, Electron Theory of Matter (ref. 10), pp. 585, 587.15 Ibid., p. 587.16 O.W. Richardson, The Electron Theory of Matter, Second Edition (Cambridge: At the Uni-

versity Press, 1916), pp. 591-606.17 Ole Knudsen, ‘‘O.W. Richardson and the Electron Theory of Matter, 1901-1916,’’ in Jed Z.

Buchwald and Andrew Warwick, ed., Histories of the Electron: The Birth of Microphysics

(Cambridge, Mass. and London: The MIT Press, 2001), pp. 227-253.18 For details about the Pickering-Fowler-Bohr case, see Hoyer, Bohrschen Atomtheorie (ref. 2),

pp. 168-173, and Nadia Robotti, ‘‘The spectrum of n Puppis and the historical evolution of

empirical data,’’ Hist. Stud. Phys. Sci. 14 (1983), 123-145.19 E.J. Evans, ‘‘The Spectra of Helium and Hydrogen,’’ Nature 92 (1913), 5.20 A. Fowler, ‘‘The Spectra of Helium and Hydrogen,’’ Nature 92 (1913), 95-96.21 N. Bohr, ‘‘The Spectra of Helium and Hydrogen,’’ Nature 92 (1913), 231-232; reprinted in

Hoyer, Bohr Collected Works. Vol. 2 (ref. 2), pp. 274-275; A. Fowler, ‘‘Series Lines in Spark

Spectra [Bakerian Lecture],’’ Philosophical Transactions of the Royal Society of London [A] 214(1914), 225-266, especially 258-263.22 Fowler to Bohr, March 6, 1915, in Hoyer, Bohr Collected Works. Vol. 2 (ref. 2), pp. 508-509.

The reference to the ‘‘vexed question’’ was to J.W. Nicholson, ‘‘The Spectra of Helium and

Hydrogen,’’ Nature 94 (1915), 642.23 Bohr, ‘‘Helium and Hydrogen’’ (ref. 21). E.J. Evans, ‘‘The Spectra of Helium and Hydrogen,’’

Philosophical Magazine 29 (1915), 284-297.24 J.J. Thomson, ‘‘On the Structure of the Atom,’’ Phil. Mag. 7 (1904), 237-265; for a discussion,

see John L. Heilbron, ‘‘J.J. Thomson and the Bohr Atom,’’ Physics Today 30 (April 1977), 23-30,

and Helge Kragh, ‘‘J.J. Thomson, the Electron, and Atomic Architecture,’’ The Physics Teacher 35

(1997), 328-332.25 J.J. Thomson, ‘‘On the Structure of the Atom,’’ Phil. Mag. 26 (1913), 792-799; idem, ‘‘La

structure de l’atome,’’ in R.B. Goldschmidt, M. de Broglie, and F.A. Lindemann, ed., La structure

de la matiere. Rapports et discussions du Conseil de Physique tenu a Bruxelles du 27 au 31 octobre

1913 sous les auspices de l’Institut International de Physique Solvay (Paris: Gauthier-Villars et Cie,

1921), pp. 1-44; Discussion, pp. 45-74. For an extensive extract in English, see Jagdish Mehra, The

Solvay Conferences on Physics: Aspects of the Development of Physics Since 1911 (Dordrecht and

Boston: D. Reidel, 1975), pp. 77-81; see also Pierre Marage and Gregoire Wallerborn, ed., The

Solvay Councils and the Birth of Modern Physics (Basel, Boston, Berlin: Birkhauser Verlag, 1999),

pp. 118-120.26 Roger H. Stuewer, The Compton Effect: Turning Point in Physics (New York: Science History

Publications, 1975), pp. 53-54.27 Thomson, ‘‘La structure de l’atome’’ (ref. 25), p. 9. For early electron explanations of the

periodic system, see Helge Kragh, ‘‘The First Subatomic Explanations of the Periodic System,’’

Foundations of Chemistry 3 (2001), 129-143.28 Sir J.J. Thomson, ‘‘On the Origin of Spectra and Planck’s Law,’’ Phil. Mag. 37 (1919), 419-446,

on 420.29 Sir J.J. Thomson, Recollections and Reflections (London: G. Bell and Sons, 1936), p. 425.


30 Bohr to Rutherford, October 16, 1913, in Hoyer, Bohr Collected Works. Vol. 2 (ref. 2), pp. 587-

589, on p. 588.31 Draft of a Letter to ‘‘Nature’’ concerning Nicholson’s Theory of Spectra (1913), in Hoyer, Bohr

Collected Works. Vol. 2 (ref. 2), p. 270.32 Bohr to Rutherford, October 16, 1913 (ref. 30), pp. 588-599.33 Rutherford to Boltwood, March 17, 1914, in Lawrence Badash, Rutherford and Boltwood:

Letters on Radioactivity (New Haven and London: Yale University Press, 1969), pp. 291-293, on

p. 292.34 Rutherford to Schuster, February 2, 1914, quoted in David Wilson, Rutherford: Simple Genius

(London, Sydney, Auckland, Toronto: Hodder and Stoughton and Cambridge, Mass. and London:

The MIT Press, 1983), p. 338.35 J. Larmor, ‘‘On the Physical Aspect of the Atomic Theory,’’ Memoirs of the Manchester Literary

and Philosophical Society 52, No. 10, 1-54; reprinted in Sir Joseph Larmor, Mathematical and

Physical Papers. Vol. 2 (Cambridge: At the University Press, 1929), pp. 344-372.36 Sir Joseph Larmor, ‘‘On Non-Radiating Atoms,’’ Phil. Mag. 42 (1921), 595; reprinted with a

postscript in Larmor, Mathematical and Physical Papers, Vol. 2 (ref. 35), pp. 632-633, on p. 633.37 Robert John Strutt Fourth Baron Rayleigh, F.R.S., John William Strutt, Third Baron Rayleigh,

O.M., F.R.S (London: Edward Arnold & Co., 1924); reprinted as an Augmented Edition with

Annotations by the Author and Foreword by John N. Howard (Madison, Milwaukee, London:

The University of Wisconson Press, 1968), p. 357.38 Arthur W. Conway, ‘‘An Electromagnetic Hypothesis as to the Origin of Series Spectra,’’ Phil.

Mag. 26 (1913), 1010-1017, on 1011, 1013. On the life and work of Conway see Edmund T.

Whittaker, ‘‘Arthur William Conway 1875-1950,’’ Obituary Notices of Fellows of the Royal Society

7 (1951), 329-340.39 John L. Heilbron, A History of the Problem of Atomic Structure from the Discovery of the

Electron to the Beginning of Quantum Mechanics (Ph.D. dissertation, University of California,

Berkeley, 1964; University Microfilms no. 65-3004), pp. 299-301.40 Arthur W. Conway, ‘‘Enhanced Series and Atomic Models,’’ Nature 94 (1914), 171-172.41 W. Peddie, ‘‘On the Structure of the Atom,’’ Phil. Mag. 27 (1914), 257-268. On Peddie (1861-

1946) see Raymond Smart, ‘‘William Peddie,’’ Edinburgh Mathematical Notes 36 (1947), 26-27.42 Peddie, ‘‘Structure of the Atom’’ (ref. 41), p. 258.43 Ibid., p. 259.44 Albert Cushing Crehore, Autobiography (Gates Mills, Ohio: William G. Berner, 1944), pp. 43-66.45 Albert C. Crehore, ‘‘On the Formation of the Molecules of the Elements and their Compounds,

with Atoms as constituted on the Corpuscular-Ring Theory,’’ Phil. Mag. 26 (1913), 25-84.46 Albert C. Crehore, ‘‘The Gyroscopic Theory of Atoms and Molecules,’’ Phil. Mag. 29 (1915),

310-332.47. Ibid., p. 312.48. Albert C. Crehore, ‘‘Construction of Compound Molecules with Theoretical Atoms, especially

the Systems of Growth of the Organic Compounds of Carbon and Hydrogen,’’ Phil. Mag. 30

(1915), 613-623.49 Crehore, ‘‘Gyroscopic Theory’’ (ref. 46), pp. 323-324.50 Albert C. Crehore, ‘‘An Atomic Model based upon Electromagnetic Theory,’’ Phil. Mag. 42

(1921), 569-592, on 592. Albert C. Crehore, The Atom (New York: D. Van Nostrand, 1920),

pp. 24-29.


51 S.R. Milner, ‘‘William Mitchison Hicks 1850-1934,’’ Obituary Notices of Fellows of the Royal

Society 1, No. 4 (1935), 393-399, especially 393-394, 397. On Hicks’s important contributions to the

vortex atomic theory, see Helge Kragh, ‘‘The Vortex Atom: A Victorian Theory of Everything,’’

Centaurus 44 (2002), 32-114, especially 43-45, 50, 69-70, 78-79.52 Professor Hicks, [Contribution to] ‘‘Discussion on the Structure of Atoms and Molecules,’’

Report on the Eighty-Fourth Meeting of the British Association for the Advancement of Science

Australia 1914 July 28-August 31 (London: John Murray, 1915), pp. 296-299, on p. 298.53 J.R. Rydberg, ‘‘The Ordinals of the Elements and the High-Frequency Spectra,’’ Phil. Mag. 28(1914), 144-149; Wolfgang Pauli, ‘‘Rydberg and the Periodic System of the Elements,’’ in Charles

P. Enz and Karl von Meyenn, ed., Wolfgang Pauli: Writings on Physics and Philosophy (Berlin,

Heidelberg, New York: Springer-Verlag, 1994), pp. 73-77.54 C.G. Darwin, ‘‘The Discovery of Atomic Number,’’ in W. Pauli, ed., Niels Bohr and the

Development of Physics: Essays dedicated to Niels Bohr on the occasion of his seventieth birthday

(London: Pergamon Press, 1955), pp. 1-11, on pp. 6-7.55 A. van der [sic] Broek, ‘‘Intra-Atomic Charge,’’ Nature 92 (1913), 372-373. H.A.M. Snelders, ‘‘A

Bio-Bibliography of the Dutch Amateur Physicist A. J. van den Broek (1870-1926),’’ Janus 61(1974), 59-72, especially 61-66; Eric R. Scerri, The Periodic Table: Its Story and its Significance

(Oxford and New York: Oxford University Press, 2007), pp. 165-169.56 Hicks, [Contribution to] ‘‘Discussion,’’ British Association Australia 1914 (ref. 52), p. 299.57 Jeans, Report on Radiation (ref. 7), p. 50.58 J.W. Nicholson, ‘‘A Structural Theory of the Chemical Elements,’’ Phil. Mag. 22 (1911), 864-

889. Wm. Wilson, ‘‘John William Nicholson 1881-1955,’’ Biographical Memoirs of Fellows of the

Royal Society 2 (1956), 209-214. On Nicholson and his atomic theory, see Russell McCormmach,

‘‘The Atomic Theory of John William Nicholson,’’ Archive for History of Exact Sciences 3 (1966),

160-184, and Clifford L. Maier, The Role of Spectroscopy in the Acceptance of an Internally

Structured Atom 1860-1920 (Ph.D. dissertation, University of Wisconsin, 1964; University

Microfilms no. 64-10,272), pp. 448-461.59 J.W. Nicholson, ‘‘The Physical Interpretation of the Spectrum of the Corona,’’ The Observatory

36 (1913), 103-112, on 103.60 Ibid., pp. 104, 103.61 J.W. Nicholson, ‘‘The Constitution of Nebulæ,’’ Monthly Notices of the Royal Astronomical

Society 74 (1914), 486-506, on 487.62 H. Bourget, Ch. Fabry, and H. Buisson, ‘‘Sur le poids atomique du nebulium et la temperature

de la nebuleuse d’Orion,’’ Comptes rendus hebdomadaries des seances de l’Academie des Sciences

158 (1914), 1017-1019. J. W. Nicholson, ‘‘Sur le poids atomique des elements des nebuleuses,’’

ibid., 1322-1323. J.W. Nicholson, ‘‘On the Nebular Line k3729,’’ Monthly Notices Roy. Astr. Soc. 74

(1914), 623-628. ‘‘Meeting of the Royal Astronomical Society. Friday, 1914 May 8,’’ The Obser-

vatory 37 (1914), 231-241, on 236-238.63 J.W. Nicholson, ‘‘The Constitution of the Solar Corona. II,’’ Monthly Notices Roy. Astr. Soc. 72

(1912), 677-692.64 Wilson, ‘‘Nicholson’’ (ref. 58), p. 211. William Wilson, ‘‘The Quantum-Theory of Radiation and

Line Spectra,’’ Phil. Mag. 29 (1915), 795-802.65 J.W. Nicholson, ‘‘The High-frequency Spectra of the Elements, and the Structure of the Atom,’’

Phil. Mag. 27 (1914), 541-564, on 557.66 Arnold Sommerfeld, Atombau und Spektrallinien (Braunschweig: Friedr. Vieweg & Sohn,

1919), p. 366, n. 1; John L. Heilbron, ‘‘The Kossel-Sommerfeld Theory and the Ring Atom,’’ Isis 58

(1967), 450-585, especially 470-479.


67 Bohr to Oseen, December 1, 1911, in Rud Nielsen, Bohr Collected Works. Vol. 1 (ref. 9),

pp. 426-431, on p. 427. J.W. Nicholson, ‘‘On the Number of Electrons concerned in Metallic

Conduction,’’ Phil. Mag. 22 (1911), 245-266.68 Niels Bohr to Harald Bohr, December 23, 1912, in Rud Nielsen, Bohr Collected Works. Vol. 1

(ref. 9), p. 563.69 Bohr to Rutherford, January 31, 1913, in Hoyer, Bohr Collected Works. Vol. 2 (ref. 2), pp. 579-

580, on p. 579.70 Bohr to Rutherford, March 21, 1913, in Hoyer, Bohr Collected Works. Vol. 2 (ref. 2), pp. 584-

585, on p. 584.71 Bohr, ‘‘Constitution of Atoms and Molecules’’ (ref. 2), p. 7; 7; 167.72 J.W. Nicholson, ‘‘The Theory of Radiation,’’ Nature 92 (1913), 199.73 Professor Nicholson, [Contribution to] ‘‘Discussion,’’ British Association Australia 1914 (ref.

52), pp. 299-301.74 Nicholson, ‘‘Constitution of Nebulae’’ (ref. 61).75 J.W. Nicholson, ‘‘Atomic Models and X-ray Spectra,’’ Nature 92 (1914), 583-584, on 583.76 Nicholson, ‘‘High-Frequency Spectra of the Elements’’ (ref. 65), p. 564. See also J.L. Heilbron,

H.G.J. Moseley: The Life and Letters of an English Physicist, 1887-1915 (Berkeley, Los Angeles,

London: University of California Press, 1974), pp. 108-110.77 Nicholson, ‘‘High-Frequency Spectra of the Elements’’ (ref. 65), p. 543, and also J.W. Nicholson,

‘‘Atomic Models and X-ray Spectra,’’ Nature 92 (1914), 630.78 A. van den Broek, ‘‘The Structure of Atoms and Molecules,’’ Nature 93 (1914), 241-242, on 242.79 J.W. Nicholson, ‘‘Atomic Structure and the Spectrum of Helium,’’ Phil. Mag. 28 (1914), 90-103,

on 93.80 Bohr, ‘‘Constitution of Atoms and Molecules’’ (ref. 2), pp. 486-490; 40-42; 200-202; J.W.

Nicholson, ‘‘A Possible Extension of the Spectrum of Hydrogen,’’ Monthly Notices Roy. Astr. Soc.

73 (1913), 382-385.81 J.W. Nicholson, ‘‘The Spectra of Helium and Hydrogen,’’ Monthly Notices Roy. Astr. Soc. 74(1914), 425-442, on 441, and also Nicholson, ‘‘Spectra of Helium and Hydrogen’’ (ref. 22).82 Nicholson, ‘‘Spectra of Helium and Hydrogen’’ (ref. 81), p. 439.83 Nicholson, ‘‘Atomic Structure and the Spectrum of Helium’’ (ref. 79), pp. 90-91, 103.84 Nicholson, [Contribution to] ‘‘Discussion,’’ British Association Australia 1914 (ref. 52), p. 300.85 F.A. Lindemann, ‘‘Atomic Models and X-Ray Spectra,’’ Nature 92 (1914), 500-501, on 501. The

detailed arguments were presented in F. A. Lindemann, ‘‘Uber die Grundlagen der Atommo-

delle,’’ Verhandlungen der deutschen physikalischen Gesellschaft 16 (1914), 281-294.86 N. Bohr, ‘‘Atomic Models and X-ray Spectra,’’ Nature 92 (1914), 553-554; reprinted in Hoyer,

Bohr Collected Works. Vol. 2 (ref. 2), p. 304; H. Moseley, ‘‘Atomic Models and X-ray Spectra,’’

Nature 92 (1914), 554. See also Hoyer, Bohrschen Atomtheorie (ref. 2), pp. 196-202, and Heilbron,

Moseley (ref. 76), pp. 105-108.87 Draft of an unmailed letter to Nature, in Hoyer, Bohr Collected Works. Vol. 2 (ref. 2), pp. 270-271.88 [Draft in Mrs. Bohr’s handwriting] in Hoyer, Bohr Collected Works. Vol. 2 (ref. 2), pp. 312-316,

on 314.89 N. Bohr, ‘‘On the Quantum Theory of Radiation and the Structure of the Atom,’’ Phil. Mag. 30(1915), 394-415, on 399; reprinted in Hoyer, Bohr Collected Works. Vol. 2 (ref. 2), pp. 392-413, on

p. 397. The earlier paper was N. Bohr, ‘‘The Spectra of Hydrogen and Helium,’’ Nature 95 (1915),

6-7; reprinted in Hoyer, Bohr Collected Works. Vol. 2 (ref. 2), pp. 385-388.


90 Nicholson, ‘‘Spectra of Helium and Hydrogen’’ (ref. 22), p. 642.91 Bohr, ‘‘Spectra of Hydrogen and Helium’’ (ref. 89), p. 6; 388. Bohr’s reply to Nature was first

returned and only appeared after ‘‘Rutherford took care of it in a hurry.’’ See also Niels Bohr to

Harald Bohr, March 2, 1915, in Rud Nielsen, Bohr Collected Works. Vol. 1 (ref. 9), pp. 571-577.92 Thomas R. Merton, ‘‘On the Origin of the ‘4686’ Series,’’ Proceedings of the Royal Society of

London [A] 91 (1915), 382-387, on 383.93 Bohr to Oseen, September 28, 1914, in Hoyer, Bohr Collected Works. Vol. 2 (ref. 2), pp. 560-

563, on p. 562.94 Bohr to Hansen, May 12, 1915, in Hoyer, Bohr Collected Works. Vol. 2 (ref. 2), pp. 516-518, on

pp. 517-518.95 Niels Bohr to Harald Bohr, April 15, 1915, in Rud Nielsen, Bohr Collected Works. Vol. 1 (ref.

9), pp. 577-579, on p. 579.96 Ludwig Foppl, ‘‘Uber die Stabilitat des Bohrschen Atommodelles,’’ Physikalische Zeitschrift 15

(1915), 707-712.97 Arnold Sommerfeld, Atombau und Spektrallinien, Dritte umgearbeitete Auflage (Braun-

schweig: Friedr. Vieweg & Sohn, 1922), p. 728.98 John William Nicholson, ‘‘Emission Spectra and Atomic Structure,’’ Journal of the Chemical

Society, Transactions 115 (1919), 855-864, on 857.99 William D. Harkins and Ernest D. Wilson, ‘‘Recent Work on the Structure of the Atom,’’

Journal of the American Chemical Society 37 (1915), 1396-1421, on 1409.100 Frederick Soddy, ‘‘Radioactivity,’’ Annual Progress Report to the Chemical Society for 1915/16

13 (1917), 245-272, on 255; reprinted in Thaddeus J. Trenn, ed., Radioactivity and Atomic Theory.

Annual Proess Reports on Radioactivity 1904-1920 to the Chemical Society by Frederick Soddy

F.R.S. (London: Taylor & Francis and New York and Toronto: Halsted Press, John Wiley & Sons,

1975), pp. 389-416, on p. 399.101 J.S. Plaskett, ‘‘The Sidereal Universe,’’ The Journal of the Royal Astronomical Society of

Canada 9 (1915), 37-56, on 44, 47.102 H.H. Plaskett, ‘‘The Origin of Spectra,’’ J. Roy. Astr. Soc. Canada 14 (1920), 269-284.103 Richard F. Hirsh, ‘‘The Riddle of the Gaseous Nebulae,’’ Isis 70 (1979), 197-212, especially 209-

212 and n. 57. Karl Hufbauer, Exploring the Sun: Solar Science since Galileo (Baltimore and

London: Johns Hopkins University Press, 1991), pp. 112-114.104 James Hopwood Jeans, ‘‘The Quantum Theory and New Theories of Atomic Structure,’’

Journal of the Chemical Society, Transactions 115 (1919), 865-871; J.H. Jeans, Report on Radiation

and the Quantum-Theory, Second Edition (London: Fleetway Press 1924).

Department of Science Studies

University of Aarhus

C. F. Møllers Alle

Building 1110

8000 Aarhus, Denmark

e-mail: [email protected]


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