We have repeated Perrin’s 1908 experiment for the determination of Avogadro’s number by determining the mean square displacement of small particles undergoing Brownian motion. Our apparatus differs from Perrin’s by the use of a CCD camera and is much less tedious to perform. We review Einstein’s 1905 analysis of Brownian motion and Langevin’s alternative derivation of the Einstein equation for the mean square displacement. We also show how Einstein’s thinking was a reflection of his belief in the validity of molecular-kinetic theory, a validity not universally recognized 100 years ago.
REFERENCES
1.
2.
A.
Einstein
, “On a new determination of molecular dimensions
,” doctoral dissertation, University of Zürich
, 1905
.3.
4.
A.
Einstein
, “Ueber einen die Erzeugung und Verwandlung des Lichtes Betreffenden Heuristischen Gesichtspunkt
,” Ann. Phys.
17
, 132
–148
(1905
).5.
A.
Einstein
, “Die von der Molekularkinetischen Theorie der Wärme Gefordete Bewegung von in ruhenden Flüssigkeiten Suspendierten Teilchen
,” Ann. Phys.
17
, 549
–560
(1905
).6.
A.
Sommerfeld
, “To Albert Einstein’s seventieth birthday
,” in Albert Einstein, Philosopher-Scientist
, edited by Paul
Schilpp
(Library of Living Philosophers
, Evanston, IL, 1949
), p. 105
.7.
J.
Perrin
, “Brownian movement and molecular reality
,” translated by F.
Soddy
(Taylor and Francis
, London, 1910
). The original paper, “Le Mouvement Brownien et la Réalité Moleculaire” appeared in the Ann. Chimi. Phys. 18 ( Serie), 5
–114
(1909
).8.
A.
Einstein
, “Autobiographical notes
” in Albert Einstein, Philosopher-Scientist
, edited by Paul
Schilpp
(Library of Living Philosophers
, Evanston, IL, 1949
), pp. 47
–49
.9.
10.
A.
Einstein
, Investigations on the Theory of Brownian Movement
, translated by A. D.
Cowper
(Dover
, New York, 1956
).11.
P.
Langevin
, “Sur la Theorie du Mouvement Brownien
,” C. R. Acad. Sci. (Paris)
146
, 530
–533
(1908
).12.
D.
Lemons
and A.
Gythiel
, “Paul Langevin’s 1908 paper on ‘On the theory of Brownian motion’
,” Am. J. Phys.
65
, 1079
–1081
(1997
), a translation of Ref. 11.13.
Polysciences, 400 Valley Road, Warrington, PA 18976 [www.Polysciences.com].
14.
See
S. P.
Smith
, S. R.
Bhalotra
, A. L.
Brody
, B. L.
Brown
, E. K.
Boyda
, and M.
Prentiss
, “Inexpensive optical tweezers for undergraduate laboratories
,” Am. J. Phys.
67
(1
), 26
–35
(1999
).15.
CRC Handbook of Chemistry and Physics
, 77th ed., edited by David R.
Lide
(CRC
, Boca Raton, FL, 1996
), pp. 6
–213
. The table title is “Viscosity of aqueous solutions.”© 2006 American Association of Physics Teachers.
2006
American Association of Physics Teachers
AAPT members receive access to the American Journal of Physics and The Physics Teacher as a member benefit. To learn more about this member benefit and becoming an AAPT member, visit the Joining AAPT page.
