A discussion of Robert Brown’s original observations of particles ejected by pollen of the plant Clarkia pulchella undergoing what is now called Brownian motion is given. We consider the nature of those particles and how he misinterpreted the Airy disk of the smallest particles to be universal organic building blocks. Relevant qualitative and quantitative investigations with a modern microscope and with a “homemade” single lens microscope similar to Brown’s are presented.

1.
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The discovery of the Brownian motion
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3.
www.physerver.hamilton.edu/Research/Brownian/index.html⟩ is the Hamilton College Brownian motion web site. The videos may be seen here or
see supplementary material at http://dx.doi.org/10.1119/1.3475685 for the videos.
4.
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6.
We are indebted to Bronwen Quarry of the Hudson’s Bay Company archives for furnishing information about the dates of travel of the brig that Douglas sailed on, the William and Ann.
7.
An authoritative and detailed biography of Brown can be found in
D. J.
Mabberley
,
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(
J. Cramer
,
Braunschweig
,
1985
).
8.
Brown’s papers, Natural History Museum of London, Box 24, Sheet No. 224. We are indebted to David Mabberley for strongly suggesting that the slips catalog be examined and to Armando Mendez of the Botany Library of the Natural History Museum for finding this sheet and mailing us a copy. Afterward, we found the contents reproduced in
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E.
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I. J.
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Lewis
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Pollen phylogeny in Clarkia
,”
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20
,
739
746
(
1971
) contains detailed measurements on many species of Clarkia including pulchella.
10.
R.
Brown
, the first paper “
A brief account of microscopical observations made in the months of June, July, and August, 1827, on the particles contained in the pollen of plants; and on the general existence of active molecules in organic and inorganic bodies
,” and the addendum “Additional remarks on active molecules,” appeared respectively in
R.
Brown
, “
A brief account of microscopical observations made in the months of June, July, and August, 1827, on the particles contained in the pollen of plants; and on the general existence of active molecules in organic and inorganic bodies
,”
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5
,
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R.
Brown
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,”
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,
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R.
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,
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4
,
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173
(
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R.
Brown
They can be downloaded ⟨sciweb.nybg.org/science2/pdfs/dws/Brownian.pdf⟩.
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B. J.
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B. J.
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Microscopy
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406
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The microscope of Robert Brown
,”
The Linnean
1
,
12
17
(
1985
). These articles describe the restoration of the Linnean Society microscope, with the first paper giving quantitative measurements on the lenses;
see also
B. J.
Ford
, “
Charles Darwin and Robert Brown—Their microscopes and the microscopic image
,”
Infocus
15
,
14
24
(
2009
).
13.
Brown had many microscopes. Upon his death, the Gardener’s Chronicle reported that at least 9 of his microscopes were sold. The French botanist Alphonse de Candolle wrote in a letter to his father, that Brown had 30 or 40 lenses, some which magnify up to 800 or 1000 times, “and he chooses from them 5 or 6 in number, with which he usually works. He obtains thus the effect of an ordinary microscope with the clarity and the reliability of a simple lens” (Ref. 7).
14.
The male part of a flower, the stamen, consists of the anther, a sack in which pollen grains develop, and a stalk it sits on, called the filament, which conveys nutrients from the flower to the anther. When the pollen is ripe, it is released because the anther bursts, a process called dehiscence. The female part of a flower, the pistil, consists of a vase-shaped style, at whose top is the stigma, a sticky structure, and at its bottom are the ovules, immature seeds containing eggs.
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A casual online search turned up many examples including
J.
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Einstein and the existence of molecules
,”
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863
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2006
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www.einsteinyear.org/facts⟩, ⟨http://www.mathunion.org/general/prizes/gauss/details/⟩ (see Gauss prize 2006 for Kiyohsi Ito).
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18.
This estimate is crude because the eye’s dynamic resolution involving consecutive positions of a single object is most likely sharper than the static resolution of two nearby objects given by the Rayleigh criterion. The Rayleigh criterion can be improved upon in circumstances where there is effectively a point source of light and sufficient collection of photons. In astronomy, the observed diffraction pattern of two close stars can be fitted to the expected overlap of individual diffraction patterns, giving the location of the two stars to much greater accuracy than the naive use of the Rayleigh criterion. See
R. C.
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,”
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,
1227
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A recent technique can pinpoint the location of a fluorescent molecule with great accuracy by appropriately fitting the observed diffraction pattern intensity it emits. See
A.
Yildiz
and
P. R.
Selvin
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Fluorescence imaging with one nanometer accuracy (FIONA): Application to molecular motors
,”
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574
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[PubMed]
19.
B. J.
Ford
, “
Brownian movement in Clarkia pollen: A reprise of the first observations
,”
Microscope
40
,
235
241
(
1992
) verified that Brown could have seen milk fat droplets undergoing Brownian motion with his Linnean ×170 lens. The article claims that the author duplicated Brown’s setup and “Within the pollen grains, ceaseless movement could be observed.” However, although the author saw the contents of the pollen, he did not see them undergoing Brownian motion (B. J. Ford, private communication). Presumably, what Ford meant is that “ceaseless movement could have been observed” with that lens;
B. J.
Ford
,
Sci. News (Washington, D. C.)
142
,
109
–109 (
1992
) erroneously concluded from this work: “When Brown looked inside the pollen grains with his microscope, he could see tiny particles, each about 1 micron across, suspended in the liquid and constantly in motion.”
20.
Scuola Normale of Pisa, ⟨gbamici.sns.it/eng/osservazioni⟩, select osservazionibiologiche.htm.
21.
J.
Heslop-Harrison
,
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(
Butterworths
,
London
,
1971
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22.
Y.
Heslop-Harrison
and
K. R.
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,”
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41
,
1233
1258
(
1977
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23.
U.
Kirsten
,
M.
Beidermann
,
G.
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R.
Dawson
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L.
Bohm
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The composition of stigmatic exudate and the ultrastructure of the stigma papillae in Aptenia cordifolia
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19
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24.
L. L.
Hoefert
, “
Ultrastructure of beta pollen. I. Cytoplasmic constituents
,”
Am. J. Bot.
56
,
363
368
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1969
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25.
The two types of particles seen by Brown were described in Ref. 1. “In consequence of their manifest motion, it has been conjectured that the longer particles of the fovilla were the incipients of the embryo, and it is by the introduction of one or more of these into the ovule that the act of impregnation is accomplished by the deposit of a rudimentary embryo in the ovule.” [Wrong] “But both Fritzsche and Mohl agree in considering many of the smaller particles of the fovilla as minute drops of oil.” [Right] “The molecular motion has been ascribed to currents in the fluid, in which the fovilla is suspended, and which, according to Fraunhofer, no precautions can possibly prevent;” [Wrong] “and, what is more important, the larger particles become blue upon the application of iodine, without however losing their property of motion, as Fritzsche has shown: they are therefore starch.” [Right] Some websites that describe how to observe pollen tubes are ⟨www-saps.plantsci.cam.ac.uk/pollen/pollen2.htm⟩, ⟨www-saps.plantsci.cam.ac.uk/worksheets/ssheets/ssheet4.htm⟩, and ⟨www.microscopy-uk.org.uk/mag/artdec99/jgpollen.html⟩.
26.
W. A.
Jensen
and
D. B.
Fisher
, “
Cotton embryogenesis: The entrance and discharge of the pollen tube in the embryo sac
,”
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,
158
183
(
1967
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27.
H.
Lewis
and
M. E.
Lewis
,
The Genus Clarkia
(
U. of California Press
,
Berkeley
,
1955
), pp.
241
392
,
356
.
28.
Thompson and Morgan, ⟨www. tmseeds.com⟩ sell packets of Clarkia pulchella (containing ≈400 seeds) for $2.25. Everwilde farms, ⟨www.everwilde.com⟩ sells packets of C. amoena and C. elegans seeds (containing ≈2000 seeds) for $2.50.
29.
IMAGEJ at ⟨http://rsbweb.nih.gov/ij/⟩.
30.
Reference 2 claimed that “…they [Brown’s molecules] were approximately of the same size; their diameter varying between 1.26 and 1.6 microns. These statements are not true, Brown was led to them because he worked with an imperfect lens at the border line of its magnifying power.” Although not strictly correct (there was nothing imperfect about Brown’s lens, magnification has a value, not a “borderline”), it seems to be the only statement in the literature which suggests that Brown’s lens affected his observations. The purpose of Ref. 2 was to add a name to Brown’s list of ten people who had observed the motion before Brown did. He called attention to observations briefly described in a paper on the usefulness of cover slips in microscopy in 1784 by Jan Ingenhousz.
31.
K. W. A.
Strehl
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Uber Luftschlieren und Zonenfehler
,”
Z. Instrumentenkd.
22
,
213
217
(
1902
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D.
Malacara
and
Z.
Malacara
,
The Handbook of Optical Design
, 2nd ed. (
Dekker
,
New York
,
2003
), p.
211
.
32.
The polystyrene latex spheres were obtained from ⟨www.tedpella.com/⟩.
33.
F.
Perrin
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Mouvement Brownian d’un ellipsoide (I). Dispersion dielectrique pour des molecules ellipsoidales
,”
J. Phys. Radium
5
,
497
511
(
1934
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R.
Vasanthi
,
S.
Rarichandran
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B.
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Needlelike motion of prolate ellipsoids in the sea of spheres
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7989
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2001
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Y.
Han
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A. M.
Alsayed
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M.
Nobili
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J.
Zhang
,
T. C.
Lubensky
, and
A. G.
Yodh
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Brownian motion of an ellipsoid
,”
Science
314
,
626
630
(
2006
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[PubMed]
34.
Instructions for the construction of such microscopes are ⟨www.microscopy-uk.org.uk/mag/artjul06/aa-lens3.html⟩ and ⟨www.funsci.com/fun3_en/usph/usph.htm⟩.
35.
Edmund Optical, 1 mm diameter ball lens #NT43-708, $22.
36.
A. C.
Hardy
and
F. H.
Perrin
,
The Principles of Optics
(
McGraw-Hill
,
New York
,
1932
), p.
58
, Eq. (71).
37.
P. M.
Morse
,
Thermal Physics
(
Benjamin
,
New York
,
1969
), p.
228
;
C.
Kittel
,
Elementary Statistical Physics
(
Wiley
,
New York
,
1958
), p.
153
;
D.
Jia
,
J.
Hamilton
,
L. M.
Zaman
, and
A.
Goonewardene
, “
The time, size, viscosity, and temperature dependence of the Brownian motion of polystyrene microspheres
,”
Am. J. Phys.
75
,
111
115
(
2007
) and textbook references therein.
38.
A.
Einstein
, “
Uber die von der molekularkinetischen Theorie der Wärme geforderte Bewegung von in ruhenden Flüssigkeiten suspendierten Teilchen
,”
Ann. Phys.
17
,
549
560
(
1905
).
39.
P.
Langevin
, “
Sur la théorie du mouvement brownien
,”
C. R. Acad. Sci.
146
,
530
533
(
1908
)
[An English translation appears in
D. S.
Lemons
and
A.
Gythiel
, “
Paul Langevin’s 1908 paper ‘On the theory of Brownian motion’
,”
Am. J. Phys.
65
,
1079
1081
(
1997
)].
40.
K.
Huang
,
Statistical Mechanics
(
Wiley
,
New York
,
1965
), p.
119
;
L. D.
Landau
and
E. M.
Lifshitz
,
Fluid Mechanics
(
Pergamon
,
Oxford
,
1978
), p.
63
. The latter also contains a problem that discusses the viscous torque on a sphere, p. 68
The viscous force on an ellipsoid moving parallel to an axis is discussed in
H.
Lamb
,
Hydrodynamics
(
Dover
,
New York
,
1945
), Sec. 339
The viscous torque on an ellipsoid rotating about an axis is calculated in
G. B.
Jeffery
, “
The motion of ellipsoidal particles immersed in a viscous fluid
,”
Proc. R. Soc. London, Ser. A
102
,
161
179
(
1922
), Eq. (36).

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