# Dismantling Hubble’s Legacy?

Michael J. Waya,b aNASA/Goddard Institute for Space Studies, New York, NY,
10029 USA bDepartment of Astronomy, Uppsala University, Uppsala, Sweden

###### Abstract

Edwin Hubble is famous for a number of discoveries that are well known to
amateur and professional astronomers, students and the general public. The
origins of these discoveries are examined and it is demonstrated that, in each
case, a great deal of supporting evidence was already in place. In some cases
the discoveries had either already been made, or competing versions were not
adopted for complex scientific and sociological reasons.

##  1 Introduction

Edwin Hubble is considered one of the titans of early 20th century
observational cosmology. He is credited in most textbooks111See Smith (2009,
p. 98). and the popular literature for a series of important discoveries made
between 1920 and 1930:

  * •

The confirmation of the Island Universe hypothesis

  * •

The classification of extragalactic nebulae

  * •

The discovery of a linear relationship between distance and velocity for
extragalactic nebulae, providing the first evidence for the expanding universe

  * •

The brightness profile of galaxies

The discoveries above are well-known to the astronomy community and most
astronomers would associate them solely with Edwin Hubble; yet this is a gross
oversimplification. Astronomers and historians are beginning to revise that
standard story and bring a more nuanced version to the public’s attention.
This paper is adding to this burgeoning reappraisal.222Some examples include
Nussbaumer & Bieri (2009); Kragh & Smith (2003); Bartusiak (2010).

As a (small) counter-narrative, William Hoyt (1980, p. 411), in his
biographical memoir of V. M. Slipher exclaims that “[Slipher] probably made
more fundamental discoveries than any other observational astronomer of the
twentieth century.”333Also see Hall (1970). Clearly some historians in the
1970s and 1980s thought that Slipher made more fundamental discoveries than
Hubble.444See contributions in this book by John Peacock, Joseph S. Tenn,
Robert Smith, Laird Thompson and Kevin Schindler for more on Slipher’s
discoveries. Yet how can that be true given all we _know_ today? In this paper
we re-examine Hubble’s discoveries in some detail in order to see if they are
better understood in a broader context. Given the focus on V. M. Slipher at
this conference we will also explicitly discuss his contributions in two of
the cases above.

##  2 Discovery of the Island Universe

The hypothesis of Island Universes has a long history going back at least to
the 18th Century with contributions by: Swedenborg (1734); Wright (1750); Kant
(1755)555Kant actually cited the work of Thomas Wright (1750)., and Lambert
(1761).666See contribution by Ayala in this book. William Herschel (1785)
initially believed that the spiral nebulae were external to the Milky Way, but
later changed his mind. Knut Lundmark (1927e, Chapter 1) does an excellent job
of explaining the origins of the Island Universe that I do not believe has
been much bettered by time.777The essence of the hypothesis, in an early 20th
century context, was that the universe was populated by many Milky Way
galaxies known then as spiral nebulae. This was opposed to the belief that the
universe consisted of a single Milky Way object with satellites such as spiral
nebulae, globular clusters and Magellanic cloud-like objects.

To get from philosophical speculation to modern quantification one must fast-
forward to the late 19th and early 20th century to find a large number of
investigations of objects termed “Nebulae” with the new art of photography and
ever larger telescopes.888See Gingerich (1987) for more on this early period.
For example, Huggins & Miller (1864) were deeply interested in the spectra of
nebulae, while astronomers such as Isaac Roberts (1903) built photographic
catalogs.999Only later was Roberts’ catalog compiled and completed by his wife
Mrs. Isaac Roberts. Using the catalogs of nebulae like that of Roberts’ and
others Lundmark (1925, pg.869) claimed that nearly 1200 spiral nebulae proper
motions had been measured at that time. We now know this claim was incorrect –
most likely it was an incorrect assessment of observational errors.101010Only
in 2012 was the proper motion of M31 possibly measured by Sohn et al. (2012)
using optical observations. The field was clearly in its infancy, but progress
on distance estimates to objects like globular clusters and spiral nebulae was
moving rapidly forward.

Table 1 lists all of the main distance estimates to spiral nebulae (known to
this author) from the late 1800s until 1930 when standard candles began to be
found in spiral nebulae.

Table 1.: Early distance estimates to Spiral Nebulae Reference | Object |  Distancea | Method
---|---|---|---
Herschel (1786) | M31 |  $<$17,200 b | color/magnitude
Nichol (1850) | “cluster” |  154,800c | magnitude comparison
– |  | 302,505 | –
Clark (1890) | M31 | 564? | nova of 1885
Clark (1903) | M31 |  $<$1000 | Size
Bohlin (1907) | M31 | 19 | parallax
Very (1911) | M31 | 4,000 | diameters
Very (1911) | M31 | 1,600 | S Andromedae
Wolf (1912) |  M31d | 32,000 | diameters
Curtis (1915b) | spirals | 10,000 | astrometry/radial velocity
Pease (1916) | NGC 4594 | 25,000 | astrometry/radial velocity
Curtis (1917) | M31 | 20,000,000 | novae
– | – | 100,000 |  novaee
Shapley (1917) | M31 | 1,000,000 | “bright stars”
van Maanen (1918) | M31 | 250 | parallax
Lundmark (1919) | M31 | 650,000 | novae
Curtis (1920) | misc | 4,000,000 | novae
– | misc | 1,000,000 | novae
– | misc | 500,000 | novae
Lundmark (1921h) | M33 | 1,000,000 | “bright stars”
Luplau-Janssen & Haarh (1922) | M31 | 326,000 |  novaef
Öpik (1922) | M31 | 1,500,000 | luminosity/mass
Hubble (1922d) | M33 | 100,000 | “stars”
Shapley (1923) | NGC 6822 | 1,000,000 | diameters/“bright stars”
Hubble (1925a) | M31/33 | 930,000 | Cepheids
Hubble (1925c) | NGC 6822 | 700,000 | Cepheids,“bright-stars”
Lundmark (1925) | M31,M87 | 1,400,000 | novae
– | – | 8,000,000 | novae
Lundmark (1925) | M104 | 56,000,000 |  Öpik (1922) method
Hubble (1926a) | M33 | 850,000 | Cepheids,Blue-Giants
Hubble (1929c) | M31 | 900,000 | Cepheids,novae
M31 value (Dec. 2012)g | M31 | 2,588,440 | 19 Methods

The ability to estimate _accurate_ distances of objects beyond the reach of
parallax only came into being with the publishing of the period–luminosity
relationship for Cepheid Variable stars by Henrietta Leavitt & Edward
Pickering (1912) and its later calibration by Ejnar Hertzsprung (1913); Henry
Norris Russell (1913)111111Using 13 Cepheids and later Harlow Shapley
(1918)121212Using 11 Cepheids of Hertzsprung’s original 13. all utilizing the
Lewis Boss (1910) catalog of proper motions.131313Although Shapley’s distances
were strongly contested by a number of people including Curtis (1921). Before
Cepheids were discovered in spiral nebulae there were a number of attempts to
use novae as standard candles to measure the distances to spiral nebulae
(Curtis 1917; Shapley 1917; Lundmark 1919; Luplau-Janssen & Haarh 1922). For
example, Heber Curtis (1917) calculated an average distance to the spiral
nebulae of 20,000,000 light years in one case and found them to be around 100
times as distant as the galactic novae in another. Lundmark obtained a
distance to Andromeda of 650,000 light years. Shapley (1918) attempted to
compare the “brightest stars” in our own galaxy to that of Andromeda and
stated:

> … the minimum distance of the Andromeda Nebula must be of order a million
> light years. At that remote distance the diameter of this largest of spirals
> would be about 50,000 light years a value that now appears most probable as
> a minimum for our galactic system.141414This is ironic given his later
> disavowals of his larger distance estimates and those related to novae in
> spiral nebulae (Shapley 1919b).

Initially the novae studies in Andromeda were difficult to reconcile with a
supernovae observed in Andromeda $\sim$35 years previously (Krueger et al.
1885; Hartwig 1885a, b; de Vaucouleurs & Corwin 1985)151515This supernova was
later denoted ‘S Andromedae’. At that time supernovae were unknown so they
were easily confused with normal novae., but given the multiple observations
of fainter novae observed in spiral nebulae Curtis (and later others) was
persuaded to drop S Andromedae and Z Centauri161616Z Centauri (in NGC 5253)
was another bright nova observed by Pickering (1895). as anomalies.

Unfortunately for the novae derived distance measurements, other observations
at that time called their accuracy into question. In the mid–1910s Curtis
(1915a) and then Lampland (1916) detected rotation in spiral nebulae, but the
former did not believe his own detection while the latter’s results were not
influential (Smith 1982, p. 31). However, additional observations of this sort
by van Maanen et al. (1916) in Messier 101 (M101) and later in Messier 33
(M33) and other nebulae (van Maanen 1923) along with the support of James
Jeans (1917) convinced many astronomers like Shapley (1919a) that novae
derived distances to spiral nebulae were impossible to reconcile without
superluminal speeds of spiral nebulae rotation.171717This was also the time
when Shapley came up with his 300,000 light year diameter Milky Way galaxy,
much larger ($>$ 30 times) than any other estimate at that time.

However, in spite of the confusing novae observations and (incorrectly)
observed rotation of spirals the evidence continued to mount that the spiral
nebulae were indeed very distant objects. The first evidence of this was a
fascinating paper by Öpik (1922) where “an expression is derived for the
absolute distance in terms of the linear speed $v_{o}$ at an angular distance
$\rho$ from the center, the apparent luminosity $i$, and $E$, the energy
radiated per unit mass.” He calculated a distance of 1.5 million light years
to M31. One year later Shapley (1923) used diameters of galaxies and the
brightness of super-giant stars in NGC 6822 to state:

> The above considerations all indicate that the distance of N.G.C. 6822 is of
> the order of a million light years. It appears to be a great star cloud that
> is at least three or four times as far away as the most distant of known
> globular clusters and probably quite beyond the limits of the galactic
> system.

This quote is particularly interesting in light of Shapley’s long standing
opposition to the Island Universe hypothesis and his super-galaxy model
(Shapley 1921), but he still would not let go of his super-galaxy model just
yet.

The issue was effectively settled by two papers from Hubble in 1925 in which
he derived distances from Cepheid variables found in M31 and M33 (Hubble
1925a) of 930,000 light years181818The original Cepheid that Hubble discovered
in M31 now has a modern ephemeris and light curve published by Templeton et
al. (2011). and in NGC 6822 (Hubble 1925c) of 700,000 light years. Note that
there were no citations to previous distance estimates in the former paper and
only a reference to Shapley (1918) for his calibration of the Cepheid variable
light curves in the latter.

Still, there was some confusion about van Maanen’s spiral nebulae observations
among his contemporaries including Knut Lundmark. Lundmark (1922c) was at
first dismissive of van Maanen’s measurements because of a preponderance of
conflicting data. However, by 1922 he had changed his mind after having
measured some of van Maanen’s plates himself (Lundmark 1927e).191919See page
17 where he states that [in 1922?] “When remeasuring Messier 33 during my stay
at Mount Wilson the situation seemed to be rather hopeless for the followers
of the island–universe theory.” Upon re-measuring the motions in M33 a couple
of years later, Lundmark concluded that van Maanen’s measurements were flawed
(Lundmark 1926c, 1927e). However, it would not be until 1935 that van Maanen
(1935) would nearly admit that his measurements of the rotation of spiral
nebulae were false. In the same issue of _The Astrophysical Journal_ Hubble
(1935) published his own measurements showing any measured rotation to be
within the measurement errors. Clearly Hubble wanted to make sure that the
persistent observations of van Maanen were dismissed by publishing his own
measurements given his (now) elevated status as one of the more highly
respected astronomers of his day.202020Christianson (1996, Chapter 11)
explains what happened in more detail. Thus it took nearly a decade after
Hubble’s 1925 paper for van Maanen’s measurements to be completely disposed of
and the Island Universe theory to be confirmed. Of course many astronomers
felt the matter had been settled all the way back in 1926.212121As mentioned
above (Lundmark 1926c) but also Luyten (1926): “It is now universally accepted
that the spiral nebula are millions of light years distant.”

Still, as mentioned by Robert Smith (2008, p. 114) “…what was missing to
settle the dispute on the spirals was a method of calculating their distances
that a great majority of astronomers could agree was accurate.” Clearly Hubble
(1925a) provided that method with his observations of Cepheids in spirals, but
a great many people before him made his observations possible. As Smith (2009,
p. 74) points out “… it is appropriate to view Hubble as confirming rather
than discovering the extragalactic nature of spirals. But, following the
dictum of John Herschel that he who proves discovers, Hubble was given the
credit.” Many important contributions to this story have been forgotten and
most textbooks in astronomy today, if they discuss the “Island Universe”
confirmation at all, bestow 100% of the credit on Hubble with scant attention
to the earlier observations that clearly supported his measurements.

At that time the use of Cepheids as standard candles was considered a very
reliable method of estimating distance. However, by the mid-1950s it had
become clear that Hubble’s distances measurements contained significant
systematic errors. Recalibration of the Cepheids by Walter Baade (1956) later
helped to show that Andromeda was twice as far away, and was actually larger
than our own Milky Way. This would have serious implications for the Big Bang
theory in the 1930s and 1940s.

###  2.1 Slipher’s Contribution to the Island Universe story

The anniversary date for this conference was intended to overlap with the
published date of Slipher’s first observation of a doppler shift in a spiral
nebula (Andromeda) on 17 September 1912 (Slipher 1913). He obtained an
astounding value of –384 km s-1. This was surprising because it was nearly an
order-of-magnitude higher than any other measured doppler shift in the heavens
at that time. By 1917 Slipher had observed 25 spiral nebulae, the largest
having a redshift of 1100 km s-1 (Slipher 1917). As we have seen above the
debate on whether spiral nebulae were Island Universes went on until Hubble
discovered Cepheids in Andromeda and other spiral nebulae. Given the 25 spiral
nebulae with radial velocities discovered by Slipher in 1917 (21 of which were
redshifts) why didn’t the astronomical community realize these objects could
not be bound to the Milky Way and must be Island Universes? In fact a number
of people did reach this conclusion including Campbell (1917) and Hertzsprung
(see Robert Smith’s chapter in this book). Still, it took several years for
Slipher to convince the community that what he was observing was real. As well
the reticence to push this interpretation by Slipher himself was related to
his modest personality.222222See Section 7 and Robert Smith’s chapter in this
book. In reality what made it difficult (and would make it difficult for _all_
proponents of an Island Universe theory) were the observations of internal
motion in Spiral Nebulae by Adrian van Maanen that began with his first
publication on the subject in July of 1916 (van Maanen 1916).232323See David
DeVorkin’s contribution to this proceedings and the first chapter in Smith
(1982). Had it not been for the erroneous observations of van Maanen it is
likely that Slipher’s observations would have provided strong support for the
Island Universe theory.

##  3 Classification of Extra-galactic Nebulae

The first systematic classification of nebulae was probably attempted by
Herschel (1786) in his paper titled “Catalogue of One Thousand New Nebulae and
Clusters of Stars.” Therein he described eight different classes of objects:

  1. 1.

Bright nebulae [93 examples]

  2. 2.

Faint nebulae [402]

  3. 3.

Very faint nebulae [376]

  4. 4.

Planetary nebulae [29]

  5. 5.

Very large nebulae [24]

  6. 6.

Very compressed and rich clusters of stars [19]

  7. 7.

Pretty much compressed clusters of large or small stars [17]

  8. 8.

Coarsely scattered clusters of stars [40]

His descriptions of the nebulae were extremely detailed using terms with
single letter abbreviations, for example: B. Bright, S. Small, v. very, e.
extremely, R. Round, M. in the middle, l. a little, g. gradually, r.
resolvable, m. milky. These were used in combinations, one of his own examples
being vgmbM: (v)ery (g)radually (m)uch (b)righter in the (M)iddle.

Later Lord Rosse (1850) gave the term spiral to some of Herschel’s nebulae by
using his new 1.8m telescope “Leviathon of Parsonstown,” but he described it
first via a drawing of M51 presented to the 15th meeting of the British
Association for the Advancement of Science (Rosse 1845; Hoskin 1982; Dewhirst
& Hoskin 1991).

Table 2.: Early Classification schemes for Extragalactic–Nebulae Reference | Notes
---|---
Herschel (1786) | “first comprehensive scheme?”
Rosse (1850) | terminology “Spirals” used
Wolf (1908) | “widely cited scheme”
Bailey (1908) | –
Pahlen (1911) | –
Bigourdan (1914) | –
Shaw (1915) | –
Curtis et al. (1918) | “bars”
Curtis (1919) | –
Jeans (1919) | Theoretical
Reynolds (1920) | Classification of spirals like Hubble (1922a)
Hubble (1922a) | Preliminary scheme
Lundmark (1926a) | Preliminary scheme
Hubble (1926b) | More complete scheme
Lundmark (1927e) | Full scheme
Shapley (1927) | –
Jeans (1928) | Tuning-fork diagram suggestion
(Hubble 1936) | Tuning fork diagram added to create complete scheme

The classification scheme of Herschel (1786) (with later modifications by son
John Herschel) was considered unwieldy and complicated, but was probably the
only one referred to consistently until new schemes in the early 20th century
such as that of Wolf (1908).242424The classification scheme of Wolf (1908) is
mentioned in a number of articles, but without a proper citation. The UGC
catalog of Nilson (1973, p. 452) cites the year 1909: “The well-known
classification system for nebulae, the Wolf code a-w with 23 standard objects,
was presented for the first time in 1909.” It was actually 1908. Wolf’s
classification scheme worked for all types of nebulae. He not only lists
specific examples of each but also includes a table of images. He labeled them
with letters ‘a–w’ (there is no letter ‘j’, but rather an ‘h’ and ‘ho’).
Another interesting scheme was developed by Bigourdan (1914).

Today Hubble (1926b) is generally given credit for coming up with the first
usable classification scheme of “Galaxies”, or as they came to be known
“Extra-galactic nebulae”. In fact the Table in his 1926 paper is titled
“Classification of Nebulae” which included both “Galactic nebulae” and “Extra-
galactic nebulae” which is an extension of his earlier work (Hubble 1922a).
Using his 1922 work as a basis, he had tried to build his Extra-galactic
nebulae classification scheme in-line with the nebular evolutionary model of
Jeans (1919).

One of the great strengths of the Hubble (1926b) paper was his formula that
described the spiral divisions:

$m_{t}=C-5log(d)$ (1)

where $m_{t}$$=$total magnitude, $d=$diameter of the nebulae, $C=$Constant
describing each object in his sequence (1–3):
Sa(1),Sb(2),Sc(3),SBa(1),SBb(2),SBc(3) where 1$=$Early, 2$=$Intermediate,
3$=$Late. Hence as a nebulae aged from “Early” to “Late” the diameter and
luminosity would change accordingly and (again) in-line with the theoretical
work of Jeans (1919). However, other models at that time (Lindblad 1927)
contradicted some aspects of Jean’s evolutionary sequence (Jeans
1919).252525In particular Lindblad (1927) states, “We do not assume a general
development from less flattened to more flattened system of higher angular
speed of rotation [like that of Jeans].” Lindblad also believed that the
centers of the the nebulae were simply unresolved faint stars – contrary to
Jeans.

David Block & Ken Freeman (2008) appear to most recently describe how Hubble’s
entire “Extra-galactic nebulae” classification scheme was remarkably similar
to one developed by John Reynolds (1920). In fact they present clear evidence
that Hubble (at this time) was aware of the Reynolds (1920) paper via an
unpublished memo written to Reynolds, which they reproduce in their book.
However, Hubble (1922a, 1926b) does not cite Reynolds (1920) in these papers,
although he does give credit to Curtis et al. (1918) for the recognition of
bars in spiral nebulae.

A year after he introduced his 1926 classification scheme, Hubble (1927f)
mentioned a paper from earlier in 1927 in which Reynolds (1927) criticizes
Hubble’s published classification scheme of 1926. Hubble again omits mention
of Reynolds (1920) while Reynolds not only mentions Hubble’s work, but an even
earlier classification scheme by Shaw (1915).

What makes Hubble’s omission of Reynolds (1920) particularly troubling is that
he accused Lundmark of plagarism not only in personal correspondence262626He
asked Lundmark to explain himself and threatened to publish his accusation
(Holmberg 1999, p. 103)., but also on page 3 of his 53-page classification
scheme article (Hubble 1926b):272727It was published a few months after
(Lundmark 1926a).

> Meanwhile K. Lundmark, who was present at the Cambridge meeting and has
> since been appointed a member of the Commission, has recently published
> (Arkiv för Matematik, Astronomi och Fysik, Band 19B, No.8, 1926) a
> classification, which, except for nomenclature, is practically identical
> with that submitted by me. Dr. Lundmark makes no acknowledgments or
> references to the discussions of the Commission other than those for the use
> of the term ‘galactic’.

This is rather remarkable because in no paper published by Hubble between 1920
and 1930 is the classification scheme of Reynolds (1920) mentioned. Lundmark
(1927e) strongly rebutted Hubble on page 24 of his 127-page paper titled
“Studies of Anagalactic Nebulae.”282828See Appendix C for Lundmark’s full
reply. The latter denotes the classification scheme of Wolf in one of the
columns292929No citation is provided, but he must be referring to Wolf (1908).
next to his own, but also mentions other work that preceded his (page 23):

> Classifications of nebulae based on photographic material have been made by
> Bailey, Curtis, Mrs. Isaac Roberts, Max Wolf, Hubble and others.

We do not have the space here to delve deeply into the personalities of Hubble
or Lundmark, yet we may get some feeling for what their contemporaries felt
about them and how they felt about their contemporaries via the limited notes
placed in papers and in their personal correspondence. Some of the latter can
be found in Smith (1982), while some specific examples in the case of Hubble
are described in Christianson (1996, Chapter 11).303030A particular quote from
Walter Adams, then the director at Mt. Wilson, is worth repeating in reference
to the conflict between Hubble and van Maanen over the distances to the
spirals: “This is not the first case in which Hubble has seriously injured
himself in the opinion of scientific men by the intemperate and intolerant way
in which he has expressed himself.” This was in reference to the conflict
between Hubble and van Maanen that Adams had to negotiate as director.

On the other hand Lundmark has been called enigmatic by Smith (1982), but at
least some of his contemporaries appreciated his general attitude. Take this
quote from Ludwik Silberstein (1925):

> … I should like to express my deep gratitude to Dr. Lundmark for having
> devoted so much attention to the discussion of this problem from a perfectly
> impartial attitude.

This was in reply to a paper by Lundmark (1924b) that critized Silberstein
(1924d) for his use of globular clusters (GCs) to determine the curvature
radius of the Universe. Lundmark felt that GCs were not distant
enough.313131It may be amusing to note that six years later Lundmark (1930d)
asked whether the GCs and Extragalactic (he used the word Anagalactic) nebulae
were related. Holmberg (1999) in his Chapter titled “Lundmark and the Lund
Observatory” also paints a picture of a complex character, but whose
bitterness towards some of his Swedish colleagues appeared to surface later in
his career when his scientific productivity was waning.

Finally, it is clear that Lundmark had been thinking of a classification
scheme for nebulae at least since 1922 (Teerikorpi 1989) and even discussed a
simplified “class of objects” in Lundmark (1925). Lundmark’s scheme for
“Anagalactic nebulae”323232His name for “Extra-galactic nebulae.” was broken
into 4 groups (see page 22 of Lundmark (1927e)): 1.) Anomalous nebulae (Aa),
2.) Globular, elliptical, elongated, ovate or lenticular nebulae (Ae), 3.)
Magellanic (“irregular”) nebulae (Am), 4.) Spiral nebulae (As), where the
degree of condensation toward the center was his main criteria. On the other
hand Hubble (1926b) separated his ellipticals by eccentricity. Spirals were
separated based on form and degree of arm development. In fact the Lundmark
and Hubble schemes were not considered the same by their
contemporaries.333333See Smith (1982, p. 152).

A year later Shapley (1927) joined in the classification attempts with a model
that incorporated aspects of the work of both Lundmark and Hubble, but his
model was not adopted. Contrary to Hubble, Shapley carefully cited his
predecessors including Bailey (1908); Reynolds (1920); Wolf (1908); Hubble
(1922a); Lundmark (1926a); Hubble (1926b).

Hubble’s classification scheme is also noted for its later tuning fork design
to separate the barred spirals from non–barred ones (Hubble 1936). Block et
al. (2004) have pointed out that Hubble was not the first to describe the
tuning fork diagram – that was originally proposed by Jeans (1928).

It is generally acknowledged that Hubble’s classification scheme became
standard because it had an evolutionary component and mathematical description
(see Equation 1) that previous schemes did not. But as should be clear from
Table 2 there were a great many classification schemes leading up to that of
Hubble’s which surely influenced him. Is it troubling that Hubble does not
readily cite two of the most important and influential schemes (before his own
was published) of Reynolds (1920) and Wolf (1908) and yet accuses a
contemporary (Lundmark) of plagarism on the basis of scant evidence? This lack
of citation by Hubble will be further discussed in Section 6.

##  4 Discovery of the “Hubble Constant”

A great deal has been written in recent years on the topic of the discovery of
the expanding universe (Nussbaumer & Bieri 2009; Shaviv 2011; Kragh & Smith
2003; Smith 1982). A number of accusations have been levelled against Hubble
(Block 2011), some of which have been discredited (Livio 2011). Several
chapters in this book contain discussions on the discovery of the expanding
universe (see chapters by Cormac O’Raifeartaigh, Ari Belenkiy, Harry
Nussbaumer, John Peacock, and Robert Smith). For that reason there is no need
to go into a great deal of detail here, but suffice it to say that this
“discovery” is even more complicated than the other stories described above.
In Table 3 one can see a steady progression of three related measures: 1.) the
solar motion with respect to the nebulae, 2.) the radius of curvature of the
universe and 3.) the linear relation of velocity and distance for the spiral
nebulae that lent support to an expanding universe model over a static one in
the first half of the 20th century. Note that papers that do not explicitly
discuss observational data are not included in the table. Some further details
on selected publications from Table 3 are worth mentioning in detail:

Table 3.: Early estimates of solar motion, curvature radius and Ho via spiral nebulae Reference | Date | Notes
---|---|---
Truman (1916)a | 1915/12/30 |  RA=20h, Dec=-20∘, V=–670km s-1 (14 spirals)
Young & Harper (1916)a | 1916/02/01 |  RA=20h24m, Dec=-12∘10′, V=–598$\pm$234km s-1
|  | (15 spirals + MC)
Paddock (1916)b | 1916/05/00 |  V=–295$\pm$202 km s-1, K=+248$\pm$88 km s-1
|  |  Using Young & Harper (1916) data.
Wirtz (1916) | 1916/08/00 | Various values of RA, Dec, V, but no K term
Wirtz (1917) | 1916/12/06 | Various values of RA, Dec, V, but no K term
Slipher (1917) | 1917/04/13 |  RA=22h, Dec=-22∘, V=–700 km s-1
de Sitter (1917) | 1917/07/00 | First estimates of R for Models A and B
Wirtz (1918) | 1917/12/00 |  K=+656 km s-1, V=–830 km s-1
Shapley & Shapley (1919) | 1918/11/00 | Magnitude vs. Velocity
Lundmark (1920) | 1920/01/26 |  K=+587 km s-1 (29 spirals, page 75)
Wirtz (1922) | 1921/10/00 |  K=+656 km s-1, V=–820 km s-1
Friedmann (1922) | 1922/05/29 |  Set M=5$\times 10^{21}M_{\hbox{$\odot$}}$, $\lambda$=0 and found
|  |  “world period”=1010 years
Wirtz (1924) | 1924/03/00 |  Distance vs. velocity: $v$(km)=2200–1200$\times$log($Dm$)c
Silberstein (1924d) | 1924/03/00 | Distance vs. velocity Relation and calculation of
|  | curvature radius (R)
Silberstein (1924e) | 1924/03/08 |  Calculates R for 11 GCd
Silberstein (1924a) | 1924/04/26 |  First distance vs. velocity plot for _GC and LMC/SMC_
Lundmark (1924b) | 1924/06/00 |  First distance vs. velocity plot for _spiral nebulae_ ,
|  |  Kspirals= +800 km s-1
Silberstein (1924b) | 1924/06/07 | Same method and data as before with new estimate of R
Silberstein (1924c) | 1924/10/00 |
Silberstein (1924f) | 1924/Late | Distance vs. velocity plot
Silberstein (1925) | 1925/01/00 |  R=7.2$\times 10^{12}$ A.U. and updated plot of distance
|  | vs. velocity for GC+MC+M33
Strömberg (1925) | 1925/06/00 | Estimates of K, but no relation found for
|  | distance vs. velocity
Lundmark (1925) | 1925/06/00 |  Re-defines: K=k+lr+mr2, First time for a
|  | variable K–term
Dose (1927) | 1926/11/00 |  K=+765$\pm$111 km s-1 for spirals (no variable K–term)
Lemaître (1927) | 1927/04/00 | Discovers that K is linearly dependent on distance
Robertson (1928) | 1928/00/00 | Expects a correlation between velocity and distance
Hubble (1929b) | 1929/01/17 | Distance vs. Velocity plot using Cepheid distances
|  | yields a linear fit
de Sitter (1930) | 1930/05/26 | Using observational data calculates R and estimates
|  | slope of velocity vs. distance
Hubble & Humason (1931) | 1931/03/00 | Updated list of distances and velocities yields
|  |  558 km s-1 Mpc-1
Oort (1931) | 1931/11/30 |  Finds Ho=290 km s-1 Mpc-1 after finding
|  | some distance inaccuracies

  * •

O.H. Truman (1916): was the first to measure the solar motion relative to the
spiral nebulae like that of Campbell (1913) and Airy (1860):
V = X cos$\alpha$ cos$\delta$ \+ Y sin$\alpha$ cos$\delta$ \+ Z sin$\delta$
343434$\alpha$=Right Ascenson, $\delta$=Declination, X,Y,Z = velocity
components of our sun through space.

  * •

George Paddock (1916): realized there may be a non-random spiral nebulae
recessional component (denoted as K). He didn’t believe it was real, but
others quickly thought otherwise. This paper contains the first appearance of
the “K correction”353535Not to be confused with the modern usage of “K
correction” which refers to resetting the colors of a galaxy to the rest
frame. in the formula for solar motion:
V = X cos$\alpha$ cos$\delta$ \+ Y sin$\alpha$ cos$\delta$ \+ Z sin$\delta$ \+
K.363636K is the average recessional velocity of spiral nebulae observed in km
s-1.

  * •

Willem de Sitter (1917): attempted to measure the radius of curvature of the
universe (R) for Einstein’s model A and his own model B in a number of ways.
In model A he made an estimate of the mass and total volume of the universe to
obtain R$\leq$5$\times$1013 Astronomical Units (A.U.)373737de Sitter (1917, p.
25) (790$\times 10^{6}$ light years). In model B he made a number of estimates
(all found in Section 6 of his paper), but perhaps the most relevant are:

    1. 1.

“If we accept the existence of a number of galactic systems whose average
mutual distances are of the order 1010 all we can say is that $\pi$R must be
several times 1010 or roughly $R>10^{11}$[A.U.].” (1.6$\times 10^{6}$ light
years)

    2. 2.

“For the lesser Magellanic cloud Hertzsprung found the distance
r$>$6$\times$109. The radial velocity is about +150 km sec-1. This gives
$R>2\times 10^{11}$[A.U.].” (3$\times 10^{6}$ light years)

    3. 3.

By averaging the velocities of 3 spiral nebulae (+600 km s-1) and their
distances (326,000 light years) he obtained $R=3\times 10^{11}$A.U.
(4.7$\times 10^{6}$ light years)

  * •

Shapley & Shapley (1919): “The speed of spiral nebulae is dependent to some
extent upon apparent brightness, indicating a relation of speed to distance
or, possibly, to mass.” [our emphasis]

  * •

Alexander Friedmann (1922): derived the first non-static solutions in addition
to the solutions of Einstein (1917) (model A) and de Sitter (1917) (model B).
He estimated the age of the universe, but we do not know where he obtained his
numbers from. He set the mass of the universe M=5$\times
10^{21}M_{\hbox{$\odot$}}$, set $\lambda$=0 and found a “world period”=1010
years. However see Ari Belenkiy’s chapter in this book. Belenkiy believes this
number should have been written 109 years.

  * •

Silberstein (1924d): estimated a distance vs. velocity relation for 7 GC, LMC
and SMC383838GC=Globular Clusters, LMC=Large Magellanic Could, SMC=Small
Magellanic Cloud), R$=$94$\times$106 light years (R=6$\times$1012 A.U.). His
estimate was later criticized by Lundmark (1924b) (among others) for only
using 7 of 16 known GC. Lundmark (1924b) states: “… there is no good reason
for selecting such an arbitrary limit for excluding objects which do not give
a rather constant value of R.” Lundmark (1924b) also complained that the low
value of K (+31 for GCs vs. +800 km s-1 for spiral nebulae) “suggests that the
former are comparatively near as compared with the latter”, implying that they
were inappropriate for calculating R. [Published March, 1924]

  * •

Silberstein (1924e): for 11 GC R$<$94$\times$106 light years
(R$<$6$\times$1012 A.U.) [Published March 8, 1924]

  * •

Silberstein (1924a): first distance vs. velocity plot with 2 fits for 11
_Globular Clusters_ including the LMC and SMC. (one fit only used 8 GC).
R$<$158$\times$106 light years (R$<$1$\times$1013 A.U.). [Published April 26,
1924]

  * •

Silberstein (1924b): used the same objects as in Silberstein (1924a) and found
R=110–126$\times$106 light years (R=7–8$\times$1012 a.u.). [Published June 7,
1924]

  * •

Lundmark (1924b): first distance vs. velocity plot for _spiral nebulae_.
Included separate plots for GC+LMC+SMC, and a variety of stellar types, but
without any lines fit to any samples since he did not feel it was warranted.
He used the novae distances to Andromeda and then used spiral nebulae
diameters (assuming constant nebular diameters and luminosities) for the other
spirals in his sample in comparison with Andromeda – his x-axis units were in
‘Distances of Andromeda Nebula.’ He also calculated K=+800 km s-1 (for
spirals), R=19.7$\times$1012 A.U. (3$\times$108 light years) for GC (but with
a very large dispersion of 26.1$\times$1012 A.U.)393939Lundmark stated: “As
the dispersion in R is 26.1$\times$1012 km and thus considerably higher than
what could be expected from the dispersions in V and r, it does not seem that
the curvature of space-time, at least for the present, can be determined with
any accuracy by using the displacements in the spectra of globular clusters.”
and 2.4–6.6$\times$1012 A.U. (3.8$\times$107–1$\times$108 light years) for
spirals.404040Note: Lundmark quoted R in units of kilometers, but it is clear
in comparisons with Silberstein’s papers and with his own distance estimates
to GCs and spiral nebulae that he must have meant to write A.U. rather than
km. Duerbeck & Seitter (1999) fit Lundmark’s data in the plot for spirals
using Lundmark’s smaller value of the distance to Andromeda of 0.2 Mpc to
yield a slope with the origin through zero of 90 km s-1 Mpc-1. If one uses an
Andromeda distance of 0.5 Mpc (derived by Lundmark using novae) one obtains 36
km s-1 Mpc-1. Also see Peacock’s contribution in this volume. [Published June,
1924]

  * •

Silberstein (1924c): R=7.2$\times$1012 A.U. (1.1$\times$108 light years).
[Published September 6, 1924]

  * •

Silberstein (1924f): distance vs. velocity plot for 11 GC, plus the LMC, SMC
and M33. Values for R were nearly the same as in Silberstein (1924d).
[Published late 1924]

  * •

Silberstein (1925): newly updated distance vs. velocity plot using 18 GC, the
LMC, SMC, and M33. Obtained R=7.2$\times 10^{12}$ A.U. (1.1$\times$108 light
years). [Published January 1925]

  * •

Strömberg (1925): after an extensive investigation into spiral nebulae (and
separately GCs) he considered correlations between distance vs. velocity and
positions on the sky (cos $\lambda$) vs. velocity. He ended his article by
stating: “In conclusion we may say that we have found no sufficient reason to
believe that there exists any dependence of radial motion upon distance from
the sun. The only dependence fairly well established is one that is a function
of position in the sky.” He plotted _two_ equivalent correlations for the
globular clusters on the same plot with wildly different slopes and stated:
“It is significant, however, that the regression-line for the clusters does
not go through the origin as expected from the theory.” [Published June 1925]

  * •

Lundmark (1925): initially believed the K-term was a constant for spirals, but
decided it was given by $K=k+lr+mr^{2}$. Here k,l,m are constants, and the r
is relative distance via the apparent diameter. Solving with 44 velocities
gave k=513,l=10.365,m=0.047.

  * •

Georges Lemaître (1927): derived a non–static solution to Einstein’s equations
and coupled it to observations to reveal a linear distance vs. redshift
relation with a slope of 670 or 575 km s-1 Mpc-1 (depending on how the data is
grouped). Radial velocities were from Strömberg (1925), distances from
apparent magnitudes given in Hubble (1926b) that were taken from Hopmann
(1921) and Holetschek (1907).

  * •

Howard Percy Robertson (1928): “… we should nevertheless expect a correlation
v$\approxeq$cl/R between assigned velocity v, distance l, and radius of the
observable world R.” [equation 17] Using the data of Hubble (1926b) for
distances and Slipher (Eddington 1923) for velocities he obtained R=2$\times
10^{27}$cm (1.3$\times 10^{14}$ A.U., 2.1$\times 10^{9}$ light years). Hilmar
Duerbeck & Waltraut Seitter (1999) have estimated his distance vs. velocity
slope as 460 km s-1 Mpc-1. Robertson also says that a similar relation to that
of equation 17 was deduced by Weyl (1923).

  * •

Hubble (1929b): used Cepheids and bright stars for distances and spiral
nebulae Doppler shifts mostly from Slipher (Eddington 1923). He found a linear
relation between distance and velocity using the data available (grouping them
two ways) and an updated solar motion equation:
V=Xcos$\alpha$cos$\delta$+Ysin$\alpha$cos$\delta$+Zsin$\delta$+kr, where the
old K is now a function linearly dependent upon distance (K=kr). He quoted a
slope of $\sim$465 $\pm$50 km s-1 Mpc-1 for 24 objects, and $\sim$513 $\pm$60
km s-1 Mpc-1 for 9 groups. He stated: “The outstanding feature, however, is
the possibility that the velocity-distance relation may represent the de
Sitter effect, and hence that numerical data may be introduced into
discussions of the general curvature of space.”

  * •

de Sitter (1930): used observational data from nebulae and calculated the
slope of the velocity vs. distance linear fit: V/cr=0.5$\times 10^{-27}$ c.g.s
(V/r$\sim$450 km s-1 Mpc-1) which for model A yields R${}_{A}=2.3\times
10^{27}$cm = 1.5$\times 10^{14}$A.U. and for model B yields R${}_{B}=2\times
10^{27}$cm = 1.3$\times 10^{14}$A.U.

Perhaps the most notable name that readers will find missing from the table
and individual descriptions is Arthur Eddington. Eddington took part in this
project in important ways that did not include actual “discoveries”:

  1. 1.

He participated in a number of important discussions with most of the authors
listed in Table 3.414141See Smith (1982)

  2. 2.

He was responsible for the re-publication and translation of Lemaître’s 1927
paper in _Monthly Notices of the Royal Astronomical Society_ (Lemaître 1931).
He initially brought Lemaître’s work to the attention of the world in his May
1930 paper (Eddington 1930).

  3. 3.

He published the final list of Slipher’s radial velocities (Eddington 1923).

  4. 4.

By some he is even considered to be the transition figure who triggered the
major paradigm change from the “static or stationary” model of the universe to
an “evolving geometry” (Ellis 1990).424242See page 98, Table 6.1.

Overall we find that Lemaître was the first to seek and find a linear relation
between distance and velocity _in the context of an expanding universe_ , but
that a number of other actors (e.g. Carl Wirtz, Ludwik Silberstein, Knut
Lundmark, Edwin Hubble, Willem de Sitter) were looking for a relation that fit
into the context of de Sitter’s Model B world with its spurious radial
velocities. This is discussed in a number of other papers in this book (see
contributions by Harry Nussbaumer, Cormac O’Raifeartaigh, and Ari Belenkiy).

###  4.1 Slipher’s Contribution to the Expanding Universe Story

Slipher’s radial velocities played a critical role in _all_ of the
publications listed in Table 3 above. Lets look at Slipher’s data in several
of the most important papers in this table.

Lundmark (1925) used Slipher’s radial velocity data of spirals to look for a
relation between distance and velocity. While he did not cite Slipher’s work,
he did state on page 866, “Mainly on account of the enthusiastic and skilful
work of V. M. Slipher we have now knowledge of 44 radial velocities of spiral
nebulae.” Why wouldn’t Lundmark cite Slipher’s work containing the 44 radial
velocities he used? In fact Slipher never published his final list of radial
velocities, the final list was found in Arthur Eddington’s book of 1923
(Eddington 1923).434343See the contribution by Robert Smith in this book, and
Slipher’s table of velocities in Eddington (1923) reproduced in Ari Belenkiy’s
contribution.

Lemaître (1927) also used the radial velocities of Slipher, but Slipher’s name
did not appear in this paper. Rather he cited the work of Strömberg (1925) as
his source. Strömberg (1925) listed 56 velocities obtained from Slipher (it
included some globular clusters in addition to spiral nebulae), but stated
“Slipher’s determinations are given without references….” Strömberg otherwise
praised Slipher in his Introduction stating “..but through the perseverance of
Professor V. M. Slipher, a fairly large number of such velocities has been
derived.” Perhaps Lemaitre could be forgiven as he was mainly a theorist, but
it’s troubling that he didn’t take the time to cite the original sources of
his data.

Hubble (1929b) used Slipher’s radial velocities for 20 out of 24 objects
444444The numbers come from Peacock’s chapter in this book. listed in his
famous Figure 1 showing a “Velocity–Distance Relation among Extra-Galactic
Nebulae”. Hubble gave no attribution to Slipher in this paper, only stating
that “Radial velocities of 46 extra-galactic nebulae are now available….”
However, he did give credit to a few people, mentioning that two of the
distances listed in his Table 1 were those of Shapley (he gave no citation),
three velocities were those of Humason, and with the exception of three
measured by himself, the rest of the visual magnitudes listed were
“Holetschek’s visual magnitude as corrected by Hopmann.”

###  4.2 Hubble Finds his Expanding Universe?

It is commonly believed that Hubble not only discovered an expanding universe,
but that he was also looking for it. The former is credible, but the latter is
not. Thus far historians have unearthed no evidence that Hubble was searching
for the clues to an expanding universe when he published his 1929 paper
(Hubble 1929b). Given the timing of events it is difficult to reconcile. There
were only a few people with knowledge of a non-static solution to Einstein’s
equations in 1928-29:

  1. 1.

Alexander Friedman: passed away in 1925.

  2. 2.

Yuri Krutkov & Paul Eherenfest who worked to get Friedman’s papers published
and negotiated with Einstein over their validity (see Belenkiy in this book).

  3. 3.

Georges Lemaître: his 1927 paper was published in French in an obscure Belgian
journal. He sent his paper to at least Einstein, de Sitter and Eddington.

  4. 4.

Einstein: discussed Lemaître’s paper with him at the 1927 Solvay conference,
454545See Belenkiy’s chapter in this book. but told him he did not believe in
his solution. For the first time Lemaître also learned from Einstein of the
Friedman 1922 and 1924 papers.

  5. 5.

De Sitter: it is not clear that he ever read Lemaître’s 1927 paper prior to
1930.

  6. 6.

Eddington: appears to have forgotten about Lemaître’s 1927 paper until he was
reminded of it in early 1930.464646See Nussbaumer & Bieri (2009), Chapter 11.

It was not until May 1930 when the papers of Eddington (1930) and de Sitter
(1930) were published that the rest of the world became aware of the non-
static solutions of Lemaître and later the earlier solutions of Friedman.

##  5 Brightness Profile of Galaxies

Reynolds (1913) was perhaps the first to attempt the measurement of the light
profile of the Andromeda Galaxy, but only across the bulge, not out to the
spiral arms. His careful measurements yielded:

$Luminosity=\frac{Constant}{(x+I)^{2}}$ (2)

where $x=$ distance from the center of the nucleus/bulge along the major axis
(out to a diameter of 7′).

Seven years later Reynolds (1927) went after more nuclei in a number of spiral
nebulae (M65, M99, M100, M94, and M64) but with mixed success at applying Eq.
2.

Three years later Hubble (1930c) describes a “Distribution of Luminosity in
Elliptical Nebulae.” In this particular case Hubble does cite the Reynolds
(1913, 1927) papers, but perhaps since Reynolds was focused on the bulges of
spiral nebulae rather than Ellipticals Hubble didn’t feel the need to ignore
his competitor. Regardless, Hubble later generalized the relation for
Ellipticals as:

$I=\frac{I_{o}}{\left(\frac{r}{a}+I\right)^{2}}$ (3)

Hubble (1930c, p. 133) also gives credit where credit is due:

> The pioneer investigations along this line are due to J. H. Reynolds, who,
> in 1913 found that the luminosity along the major axis of M 3I, out to 7′
> from the nucleus, could be represented by the formula L=Constant/(x+I)2.

Here we have a (unique?) case where Hubble has properly cited and praised his
predecessor. This relation is now referred to as the Hubble Luminosity
Profile, but perhaps it would be more properly named the Reynolds–Hubble
Luminosity Profile.

In the end it is perhaps not so relevant as there are a number of other far
more popular profiles in use today including the de Vaucouleurs (1948), King
(1962) and Sérsic (1963) profiles.

##  6 Combing Through the Literature

It may be possible to better quantify Hubble’s unwillingness to cite his
predecessors by examining the literature more closely. Most bibliographies in
the 1920s were not compiled at the back of each article as it is done today. A
work was cited by the person’s name and the citation would be contained in a
footnote at the bottom of the same page. For this reason the SAO/NASA
Astrophysical Data Service (ADS) does not have complete bibliographies for the
papers of the period of interest. This author took all of the scientific
publications of Hubble from 1920 through 1930 and attempted to put together a
pseudo-bibliography for each paper. Thankfully Hubble did not write that many
papers in comparison with Lundmark (see Appendices A and B). A pseudo-
bibliography here means that if someone’s name was mentioned in the context of
a previous publication but no bibliographic information was included it was
included as a citation. Full citations are also included in the counting.

Knut Lundmark was chosen as a comparative figure to Hubble as he was probably
considered by his peers to be a figure of equal stature during the 1920s
474747This was more so in the beginning of the 1920s, less so in the latter
after Hubble’s many discoveries.. Lundmark wrote many more papers than Hubble,
but ADS does not have a complete set of the papers he wrote during this period
of time. A handwritten book was obtained 484848The author is unknown, hence
there is no citation for it. from the Uppsala University Library that
contained a listing of all of Lundmark’s papers in his career (even it is not
complete, but more so than ADS). Some of the papers missing from ADS found in
this book are included in Appendix B. Papers were not included that were
considered popular science.494949Lundmark wrote at least 35 articles for the
Swedish magazine _Populär Astronomisk Tidskrift_ , none of which are presently
in ADS (There is an effort to make it so). Some of the articles are on
historical figures such as Tycho Brahe, obituaries, and discoveries or reports
from meetings. He also wrote several popular science books and encyclopedia
articles that are not included. The recording of citations in Lundmark’s
papers were approached in the same manner as for Hubble.

To ensure these are relatively comparable figures ADS was used to see how
often other authors mentioned Lundmark and Hubble in their articles. Using the
ADSLabs Fulltext Service505050Currently residing at
http://labs.adsabs.harvard.edu/fulltext Statistics were compiled on how many
times authors mentioned Lundmark and Hubble by name from 1920 through 1930.
Astronomers did not consistently include a full citation to other authors’
works, but often only referenced the author’s name. All papers have been
eliminated where Lundmark or Hubble have cited/mentioned
themselves.515151There are certain to be a number of complaints about this
methodology. For example, perhaps Lundmark simply likes to includes lots of
citations, or Hubble only cites “big shots”, etc. Those and others are
certainly valid complaints, but they should not distract one from making an
attempt. From Appendices A and B, it is apparent that Lundmark did not simply
fill up his papers with citations for the sake of doing so, but because he had
a broad knowledge of the scientific literature in his field of study. This is
confirmed by Holmberg (1999, p. 130):

> He had read widely and perhaps knew the astronomical literature better than
> most astronomers…

While Hubble was inconsistent in his citations, this inconsistency was not
necessarily reflected by the status of the individual he did or did not cite.
To attempt to properly quantify these kinds of tendencies would require a much
larger and sophisticated effort than that provided herein; nonetheless, it is
clear from Figure 1 that in the early half of the 1920s it is Lundmark who is
“cited” more frequently, while in the latter half it is Hubble. This is not
surprising given not only the facilities with which Hubble was able to conduct
his research (including the largest aperture telescope in the world at Mt.
Wilson), but also Hubble’s success at promoting himself and Mt. Wilson as
described above.

Figure 1.: Top: Black are the number of publications 1920 through 1930 that
cite Knut Lundmark per year, white are the total number of citations per year.
Bottom: The same for Hubble.

Figure 2 shows how often Lundmark and Hubble cited other authors.
Unfortunately there is no way to accomplish this within ADS at
present.525252The author is currently working with leading text data mining
researchers to make this possible in the future. To obtain these numbers was
difficult and required reading through every paper and counting the number of
actual citations, not just names, to authors.535353By citation we are being
flexible in that a citation can simply refer to an author’s work by name
(without a journal reference), but they can only be “cited” once per paper
(this is sometimes difficult to discern). Figure 2 shows a clear trend in that
Lundmark cites authors almost twice as frequently as Hubble. If one allows all
of Lundmark’s publications (Hubble’s longest was 65 pages, while Lundmark’s
has 3 over 100 including one over 250) Lundmark is still over a factor of two
higher in citation rate per page.

Figure 2.: Top Left: Citations per page in Lundmark 1920–1930 publications of
less than 70 pages. Top right: Citation per page in all Lundmark 1920–1930
publications. Bottom left: Hubble citations per page in all publications
1920–1930.

A more specific comparison can be made by examining two papers by Hubble and
one by Lundmark (Figure 3). The first one of Hubble was 51 pages in length
(Hubble 1926a); not including pages with tables or photos taking up a full
page it is only 41. A second Hubble paper (Hubble 1929c) is 63 pages in
length; without full page tables/photos only 41. For Lundmark a paper 195
pages in length was chosen (Lundmark 1927e) (91 eliminating full pages with
tables/photos). In both Hubble and Lundmark’s papers the number of author
names per paper was counted (not including their own names).545454This is a
looser criterion from that above where only _citation_ related names were
compiled. In the two Hubble papers there were a total of 66 and 75 names
mentioned (many repeated of course), which comes to 1.61 and 1.83 names per
page. For Lundmark’s paper there were 423 names mentioned which comes to 4.65
names per page.

Figure 3.: Top Left: Number of author names (including duplicates) found in
(Hubble 1926a). Top Right: same for (Hubble 1929c). Lower Left: Same for
(Lundmark 1927e). Note that all of the scales on the y-axes are distinct, as
are the x-axes between the top two and bottom plot.

Of course the raw numbers as presented in Figure 3 should be renormalized to
the number of pages, but one can see that even dividing Lundmark’s numbers by
a little over a factor of two would reveal that he still mentioned his
colleagues much more frequently than Hubble. It should also be obvious to the
knowledgeable reader that all of the more highly-cited names shown are the
expected authors in this particular domain.

One could also extend this type of study in numerous directions to better
quantify these effects. For example, it could be interesting to compare how
often authors cite others who their work explicitly relies upon. Do the works
on classification of Herschel, Reynolds, or Wolf show up in the classification
works of Lundmark or Hubble? We know from above that Reynolds (1920) was never
found in any of Hubble’s work, but what about the others who would have
influenced Hubble?

##  7 The Making of Mythic Heroes

It would be inappropriate to suggest that Hubble was irrelevant to the history
astronomy, but is clear that many of the advances discussed above would have
happened within a short period of time of their original discovery even if
Hubble had never worked as an astronomer.555555As a (distant) analogy lets
consider the accomplishments of Alexander the Great. Were his accomplishments
inevitable because the Macedonian state was ready for a strong ruler after the
death of his father Philip? Wasn’t the Macedonian version of the Greek phalanx
with its longer spear and the high level of training required to master this
technology in place well before Alexander? If one answers yes to these things,
then perhaps another “strong man” could have come to the helm of the state and
accomplished much the same as Alexander. Or if Philipp had lived he surely
would have attempted many of the same things that Alexander attempted. This
may be contrary to the assertion by Smith (2009, p. 72) that technological
determinism alone does not explain Hubble’s discoveries. Indeed, technological
determinism, the belief that such discoveries were inevitable given facilities
such as the large telescopes at Mt. Wilson, is not needed. Instead one may
consider historical determinism “lite.” Clearly there were many astronomers
working in these topics and steady progress was being made in each field. If
Hubble had not found Cepheids in spiral nebulae in 1924/25, then someone else
surely would have within a few years. Lundmark’s classification scheme, or the
earlier scheme of Reynolds for spirals, could have easily replaced Hubble’s at
some level and the linear distance-velocity relation had already been
postulated by Lemaître in 1927. Without Hubble it is clear that within a short
period of time someone else would have been given credit for each of these
initial discoveries, Stigler’s Law of Eponymy notwithstanding (Merton 1965;
Stigler 1980).565656The most famous quote from Stigler’s paper is: “No
scientific discovery is named after its discoverer.” Hubble’s success in
gaining credit for his classification scheme and linear distance-velocity
relation may be related to his verification of the Island Universe hypothesis
– after the latter, his prominence as a major player in astronomy was
affirmed. As pointed out by Merton (1968) credit for simultaneous (or nearly
so) discoveries is usually given to eminent scientists over lesser-known
ones.575757This has been termed “The Matthew Effect.”

One may also consider the competition between the Lick, Lowell and Mt. Wilson
Observatories in early observational cosmology. Because Lowell Observatory did
not enjoy a high level of esteem, 585858The poor reputation was initially due
to Percival Lowell’s claim to have discovered canals engineered by intelligent
beings on Mars. it may have taken Slipher more effort than other professional
astronomers to convince the community of the validity of his initial
discoveries (see contributions by Joseph S. Tenn, Robert Smith and others in
this book). In addition, Slipher had a modest personality and was not given to
boasting or promoting his accomplishments in public. On the other hand,
consider Lundmark or Wirtz who did not have regular access to telescopes,
instrumentation and support facilities like that of Lick (Clark 36-in [1888]
and Crossley 36-in [1905]), Mt. Wilson (60-in [1908] and Hooker 100-in
[1917]), or Yerkes (40-in [1895]).595959Lundmark did visit and observe at Mt.
Wilson before his falling out with Hubble over their classification schemes.
He also spent time at Lick and Mt. Wilson over a period of two years (1921-22)
thanks to the Sweden-America foundation (Holmberg 1999, p. 94). At that time
he was able to borrow plates from Lick Observatory. In 1929 and in 1932 he
again visited several American observatories (including Mt. Wilson) to utilize
their plate collections for his Lund General Catalogue project (Ibid., pp.
109-116). Did Lundmark and Wirtz have to write more cogent and highly
interesting/readable papers to get the community to follow their research in a
“competition for attention” (Collins 1975, p. 480)? If so, then we know that
Lundmark succeeded at some level because his 1920 thesis (Lundmark 1920) was
read by astronomers such as Shapley and van Maanen before he had even arrived
at Mt. Wilson and Lick Observatories (Holmberg 1999, p. 94). In fact,
Lundmark’s work was so highly regarded that a “Memorial Volume” was edited by
Martin Johnson (1961) and published three years after Lundmark’s death. It
included contributions by a number of highly regarded astronomers such as
Milton Humason (p. 26), Harlow Shapley (p. 37), Boris Vorontsov-Velyaminov (p.
43), Fritz Zwicky (p. 55) and Gustaf Strömberg (p. 95).

Of course language may have also played a role. None of Wirtz’s major works
were published in English,606060Much of observational cosmology research was
being produced at American observatories, while much of the theory was being
promoted by Eddington, de Sitter and others in English language publications
in Europe during the trying economic times after World War I. whereas Lundmark
wrote mainly in English language journals from around 1920.616161Lundmark also
published in Swedish in popular science publications and in English and
Swedish in journals like _Arxiv för Matematik, Astronomi och Fysik_ , and
_Lund or Uppsala Observatory Reports_. Is it possible that an astronomer like
Hubble coming from the premier observatory didn’t need to be as explicit in
his citing of previous work because people had to read and utilize his results
regardless of the quality of the background scholarship?

There is also the issue of the relative decline of research activities at
smaller institutions that took place in the U.S.A. (and Europe) around the
turn of the century given that the latest observational astronomy research
required large amounts of capital (Lankford 1997, Chapter 7). As well, the
First World War did not do anything positive for the facilities at European
institutions in this sense. Simply consider Shapley’s move from Mt. Wilson to
Harvard around 1925. Clearly he knew he was giving up access to one of the
finest observatories in the world to work at an institution with inferior
equipment, although as director of Harvard Observatory he was to obtain
sufficient research funding for otherwise large-scale projects.

One should take account of these changes in order to better quantify how the
attitudes of scientists working at the premier institutions could have changed
and how credit for discoveries was subsequently awarded. While it may be a
stretch to quote from William Pitt that “Unlimited power is apt to corrupt the
minds of those who possess it.” One should not rule out such effects on the
minds of successful scientists. Aggression and competition surely play some
kind of role – a role which sociologists have already explored in a number of
scientific contexts, including the “necessity” to defend one’s position and
ideas (Lankford 1997, p. 187). Collins (1975, p. 482) has also suggested that
as scientists move into higher status positions they may take on more
aggressive roles. Certainly we have seen aspects of this behavior in Hubble in
his footnote dispute with Lundmark (also see Chapter 11 in Christianson
(1996)), and his persistent tendency to defend his discoveries as sole
achievements of himself and Mt. Wilson.626262Hubble wrote to de Sitter in 1930
(Hubble 1930b) in response to de Sitter’s recent publication (de Sitter 1930)
of a velocity-distance relation and his lack of sufficient credit to Hubble:
“I consider the velocity-distance relation, its formulation, testing and
confirmation, as a Mount Wilson contribution and I am deeply concerned in its
recognition as such.”

It has been argued (see Kragh & Smith 2003) that much of Hubble’s fame at-
large came after his death in 1953.636363Although in 1934 Lundmark was already
lamenting a wave of “Hubbleianism” (Holmberg 1999, p. 100) This retrospective
view of Hubble’s accomplishments would certainly fit in with the well-known
hypothesis of Thomas Kuhn (1962) that:

> There is a persistent tendency to make the history of science look linear or
> cumulative, a tendency that even affects scientists looking back at their
> own research.

Of course, a similar analysis could apply to many scientific discoveries of
importance in the early 20th century. An outstanding example is Henrietta
Levitt’s discovery of a period–luminosity relation for Cepheid variable stars
and the number of scientists it took to place it on a reliable and accurate
footing.

##  8 Conclusion

Can one say anything definitive about the credit that Hubble has received for
the seminal discoveries discussed herein, and his lack of acknowledgement of
the work of others? At the present time it does not seem possible to quantify
these observations. The line of research presented in this work is only an
initial attempt. With new text data mining technologies growing in strength
one should be able to better quantify some of the assertions above in the near
future. Given what is known today it would not be fair to suggest that Hubble
was a Lavoisier-like figure who regularly claimed the discoveries of others as
his own (Butterfield 1959, pp. 206-9), but that he was inconsistent in
awarding credit.

Future researchers are certain to mine the literature in detail to examine how
major scientists cited (or not) their colleagues, but will this influence the
writers of today? Perhaps this could be accomplished by demonstrating that
over the long-term one may be discredited for neglecting to cite relevant work
that one relied upon.

Take two recent books from the 2000s that were highly read in the scientific
community: Stephen Wolfram’s book (Wolfram 2002) and that of Roger Penrose
(Penrose 2005). Wolfram’s book contains almost no citations to other work,
while Penrose makes a valiant attempt to cite others for a book even broader
in scope than Wolfram’s. Needless to say Wolfram was pilloried in the
scientific and popular press for this lack of attribution and general belief
that his ideas have broader application than possible (e.g. Casti 2002; Hayes
2002; Economist 2002). Perhaps the general public agrees as well: Wolfram has
received 3 stars out of 5 (from 344 reviews) on Amazon.com as of 2012/12/05
(with a large number of 1 stars (102) and 2 stars (61). Penrose received 4 out
of 5 (from 204 reviews) with very few 1 (12) or 2 (12) stars. Penrose’s
bibliography is 30 pages in length (pp. 1050–1080) and has received rather
more favorable reviews (e.g. Johnson 2005; Blank 2006).

How credit is awarded for a discovery is often a complex issue and should not
be oversimplified – yet this happens time and again. Another well-known
example in this field is the discovery of the Cosmic Microwave Background (see
Alpher & Herman (1988); Gribbin (1998); Kragh (1999)).

The problem is larger than awarding credit within a given field as outsiders
pick anecdotal stories from astronomy, and not only get them wrong, but
oversimplify them.646464A recent example would be Taleb (2010) in his
_Inadvertent Discoveries_ subsection of Chapter 11 (on page 168 of the
paperback edition) where he discussed the discovery of the Cosmic Microwave
Background Radiation. This can also happen in the case of professional
astronomers/physicists (see Greene 2011).656565To take one of many mis-
statements in this piece: “In 1929, the American astronomer Edwin Hubble
discovered that distant galaxies are all rushing away from us.” One only needs
to read a smattering of the contributions in this book to understand how
misguided Greene was in his assumptions. Perhaps, as a community, astronomers
can learn to do better and this book could be the beginning, at least in this
particular domain.

#### Acknowledgments

This research has made use of NASA’s Astrophysics Data System Bibliographic
Services.

Thanks are due to the ever-efficient librarians at The Goddard Institute for
Space Studies, Zoe Wai and Josefina Mora, without whom many of the references
in this paper would have taken much more time to locate. I also wish to thank
Samuel Regandell, Bengt Edvardsson and Kjell Lundgren of the Astronomy
department at Uppsala University for their help in locating (and scanning)
some hard-to-obtain manuscripts by Knut Lundmark in their basement storage. My
wife Elisabeth also deserves praise for patiently listening to my many
complaints about the literature and soothing my stress from co-organizing this
conference and Proceedings.

This work has also benefited from comments by Bengt Edvardsson, John Peacock,
and Jeffrey Scargle and my excellent co-Editor Deidre Hunter.

##  Appendix A Hubble’s published papers 1 Jan. 1920 through 31 Dec. 1930

No. | Reference | Pages | Citations |  Notesa
---|---|---|---|---
1 | Seares & Hubble (1920a) | 15.0 | 15 | +
2 | Hubble (1920) | 18.0 | 15 | +
3 | Seares & Hubble (1920b) | – | – | See ref. 1
4 | Hubble (1921) | – | – | N/A not Hubble’s work?
5 | Hubble (1922b) | 39.0 | 44 | +
6 | Hubble (1922c) | 38.5 | 17 | +
7 | Hubble (1922a) | – | – | See ref. 5
8 | Hubble & Lundmark (1922a) | 2.0 | 4 | +
9 | Hubble (1922d) | – | – | See ref. 6
10 | Hubble (1923a) | 1.0 | 3 | *
11 | Hubble (1923b) | 2.5 | 2 | –
12 | Hubble (1925d) | 26.0 | 37 | !
13 | Hubble (1925a) | 3.0 | 2 | –
14 | Hubble (1925b) | – | – | See ref. 13
15 | Hubble (1925c) | – | – | See ref. 12
16 | Hubble (1926c) | 39.5 | 56 | +
17 | Hubble (1926b) | – | – | See ref. 17
18 | Hubble (1926d) | 52.0 | 28 | –
19 | Hubble (1926a) | – | – | See ref. 16
20 | Hubble (1926e) | 2.0 | 5 | *
21 | Hubble (1927e) | – | – | N/A Popular Article
22 | Hubble & Duncan (1927a) | 5.5 | 7 | –
23 | Hubble (1927a) | – | – | See ref. 34
24 | Hubble & Humason (1927) | – | – | N/A written in 1934?
25 | Hubble (1927d) | – | – | N/A written in 1936?
26 | Hubble (1927c) | – | – | See ref. 10
27 | Hubble (1927b) | 3.0 | 2 |
28 | Hubble & Duncan (1927b) | – | – | See ref. 22
29 | Hubble (1927f) | 5.5 | 5 | +
30 | Hubble (1928) | 4.0 | 6 | *
31 | Hubble (1929a) | – | – | N/A Article “excerpt”
32 | Hubble (1929d) | – | – | See ref. 33
33 | Hubble (1929c) | 62.0 | 63 | !
34 | Hubble (1929b) | 6.0 | 8 | +
35 | Hubble (1930c) | – | – | See ref. 37
36 | Hubble & Duncan (1930) | 1.0 | 2 | +
37 | Hubble (1930a) | 17.0 | 19 | +

##  Appendix B Lundmark’s published papers 1 Jan. 1920 through 31 Dec. 1930

No. | Reference | Pages | Citations |  Notesa
---|---|---|---|---
1 | Lundmark (1920) | 78.0 | 256 | –
2 | Lundmark (1921a) | 2.0 | 10 | –
3 | Lundmark (1921b) | 2.0 | 10 | –
4 | Lundmark (1921e) | 1.5 | 1 | –
5 | Lundmark (1921d) | 15.0 | 27 | !
6 | Lundmark (1921g) | 1.5 | 7 | *
7 | Lundmark (1921c) | 3.0 | 11 | !
8 | Lundmark (1921f) | 3.0 | 5 | *
9 | Lundmark (1921h) | 4.0 | 15 | !
10 | Lundmark (1922i) | 3.5 | 13 | –
11 | Lundmark & Luyten (1922d) | 4.0 | 13 | +
12 | Lundmark (1922h) | 2.0 | 1 | *
13 | Lundmark (1922l) | 1.0 | 2 | *
14 | Lundmark (1922b) | 1.0 | 7 | *
15 | Lundmark (1922j) | 10.0 | 39 | !
16 | Lundmark (1922f) | 0.5 | 2 | *
17 | Lundmark (1922c) | 8.0 | 18 | +!
18 | Lundmark & Luyten (1922b) | 2.0 | 13 | +!
19 | Lundmark & Luyten (1922a) | 16.0 | 44 | –
20 | Lundmark (1922k) | 9.0 | 22 | +
21 | Lundmark (1922a) | 9.0 | 17 | +
22 | Lundmark (1922g) | 5.0 | 28 | +
23 | Lundmark (1922d) | 1.5 | 14 | *+!
24 | Lundmark & Luyten (1922c) | 0.3 | 3 | –
25 | Hubble & Lundmark (1922b) | 2.0 | 4 | +
26 | Lundmark (1922e) | 8.0 | 3 | –
27 | Lundmark & Luyten (1923b) | 2.0 | 2 | –
28 | Lundmark & Luyten (1923e) | 2.0 | 9 | +!
29 | Lundmark & Luyten (1923d) | 3.0 | 6 | +!
30 | Lundmark (1923b) | 25.0 | 28 | –
31 | Lundmark & Luyten (1923a) | 4.5 | 7 | +
32 | Lundmark & Luyten (1923c) | 2.5 | 5 | +
33 | Lundmark (1923a) | 2.0 | 4 | +
34 | Lundmark (1924b) | 24.0 | 62 | +
35 | Lundmark (1924c) | 4.0 | 7 | +
36 | Lundmark (1924a) | 2.5 | 7 | +
37 | Lundmark (1925) | 31.0 | 110 | +!
38 | Lundmark (1926d) | 6.0 | 6 | +
39 | Lundmark (1926e) | – | – | ?
40 | Lundmark (1926c) | – | – | See ref. 38
41 | Lundmark (1926a) | 2.0 | 5 | *
42 | Lundmark (1926b) | 6.0 | 13 | +
43 | Lundmark (1927a) | 6.0 | 5 | –
44 | Lundmark (1927d) | – | – | ?
45 | Lundmark (1927b) | – | – | ?
No. | Reference | Pages | Citations |  Notesa
---|---|---|---|---
46 | Lundmark & Luyten (1927b) | – | – | ?
47 | Lundmark (1927c) | 15.0 | 63 | +
48 | Lundmark & Luyten (1927a) | 2.0 | 3 | +
49 | Lundmark & Luyten (1927c) | 2.0 | 5 | +
50 | Lundmark (1927e) | 133.0 | 195 | !
51 | Lundmark (1928c) | – | – | ?
52 | Lundmark (1928a) | 6.0 | 10 | +
53 | Lundmark & Ark (1928) | 8.0 | 14 | +
54 | Lundmark (1928b) | – | – | ?
55 | Lundmark (1930d) | 1.5 | 4 | *
56 | Lundmark (1930b) | 1.0 | 1 | *
57 | Lundmark (1930c) | 30.0 | 16 | *
58 | Lundmark (1930a) | 3.0 | 5 | *

##  Appendix C Lundmark’s reply to Hubble May 1927

Lundmark’s reply to Hubble’s accusation of plagiarism was presented as a paper
to the Royal Society of Science of Upsala on May 6, 1927 and later published
in the _New Proceedings of the Royal Society of Science of Upsala_ 666666Nova
Acta Regiae Societatis Scientiarum Upsaliensis, Volumen Extra Ordinem Editum
1927 and provides a unique look at how at least one of Hubble’s peers viewed
him at that time. I produce this quote (verbatim) here since this volume was,
until recently, very difficult to obtain.

> “In his paper, Extragalactic nebulae, Aph. J. 64:321, 1926, E. P. Hubble
> makes an attack on me which is written in such a tone that I hesitate to
> give any answer at all. Still, I may take the occasion to state a few facts.
>
> I was present at the Cambridge meeting of the Astronomical Union.
>
> I was not then a member of the Commission of Nebulae.
>
> I did not have any, access whatsoever to the memorandum or to other writings
> of E. P. Hubble, neither did I have access to the report of nebulae (which
> does not give details of Hubble’s classification) until at the end of the
> meeting, neither did I recognize until I obtained a letter from Hubble at
> the end of 1926 that he had made another classification of nebulae than the
> one published in his paper, A general study of the Diffuse Galactic Nebulae,
> Mt Wils. Contr. No. 241, 1922.
>
> As much as I heard of the discussion in the committee of nebulae the only
> question was if the terms $\gg$galactic$\gg$ and $\gg$extragalactic
> nebulae$\gg$ should be accepted, From the discussion I got the impression
> that the intention of Hubble was to force through his nomenclature, One of
> the members told me outside the discussion that Hubble had suggested the
> subdivision $\gg$logarithmic spirals$\gg$ but I did not understand that this
> suggestion was given in any memorandum to the Union, Now when reading
> Hubble’s paper I am glad to note that he seems not to have carried out the
> unhappy idea introducing the term $\gg$logarithmic spirals$\gg$ Slight
> changes in his classification might have been introduced since the Cambridge
> meeting.
>
> Hubble’s statement that my classification except for nomenclature is
> practically identical with the one submitted by him is not correct. Hubble
> classifies his subgroups according to eccentricity or form of the spirals or
> degree of development while I use the degree of concentration towards the
> centre. As to the three main groups, elliptical, spiral and magellanic
> nebulae it may be of interest to note that the two first are slightly older
> than Hubble and myself. The term elliptical nebulae thus is used by
> Alexander in 1852 and the term spiral by Rosse in 1845; The importance of
> the magellanic group has been pointed out by myself Observatory 47, 277,
> 1924 earlier than by Hubble. _As to Hubble’s way of acknowledging his
> predecessors I have no reason to enter upon this question here._ ” (the
> latter is our emphasis).

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