94 STATISTICAL PHYSICSnation in terms of molecular collisions was not entirely abandoned. Take, for
example, the case of Louis Georges Gouy, who did some of the best nineteenth
century experiments on Brownian motion. He agreed with the remark by Naegeli
and Ramsey, but conjectured that the molecules in liquids travel in organized
bunches so that an individual kick imparted to a suspended particle would be due
to the simultaneous action of a large number of molecules.
Gouy was also the first to note that it was not easy to comprehend Brownian
motion from a thermodynamic point of view. It seemed possible to him—at least
in principle—that one could construct a perpetuum mobile of the second kind
driven by those ceaseless movements (It should be mentioned that the explicit dis-
proof of this statement is delicate. The best paper on this question is by Leo Szi-
lard [S4].). This led Gouy to express the belief that Carnot's principle (the second
law of thermodynamics) might not apply to domains with linear dimensions of the
order of one micrometer [G2].
Poincare—often called on at the turn of the century to pronounce on the status
of physics—brought these ideas to the attention of large audiences. In his opening
address to the 1900 International Congress of Physics in Paris, he remarked, after
referring to Gouy's ideas on Brownian motion, 'One would believe seeing Max-
well's demon at work' [P5]. In a lecture entitled 'The Crises of Mathematical
Physics,' given before the Congress of Arts and Science in St. Louis in 1904, he
put Carnot's principle at the head of his list of endangered general laws: '[Brown]
first thought that [Brownian motion] was a vital phenomenon, but soon he saw
that inanimate bodies dance with no less ardor than the others; then he turned the
matter over to the physicists.. .. We see under our eyes now motion transformed
into heat by friction, now heat changed inversely into motion. This is the contrary
of Carnot's principle' [P6].
- The Overdetermination of N. In 1905, Einstein was blissfully unaware of
the detailed history of Brownian motion. At that time, he knew neither Poincare's
work on relativity nor the latter's dicta 'On the Motion Required by the Molec-
ular Kinetic Theory of Heat of Particles Suspended in Fluids at Rest,' as Einstein
entitled his first paper on Brownian motion [E2]. In referring to fluids at rest, he
clearly had in mind the fluids in motion dealt with in his previous paper, finished
eleven days earlier. The absence of the term Brownian motion in this title is
explained in the second sentence of the paper: 'It is possible that the motions dis-
cussed here are identical with the so-called Brownian molecular motion; the ref-
erences accessible to me on the latter subject are so imprecise, however, that I
could not form an opinion about this.'
This paper, received by the Annalen der Physik on May 11, 1905, marks the
third occasion in less than two months on which Einstein makes a fundamental
discovery bearing on the determination of Avogadro's number. The three methods
are quite distinct. The first one (submitted to the Annalen on March 18, 1905),
in which use is made of the long-wavelength limit of the blackbody radiation law,