66 STATISTICAL PHYSICSadvance warning to the reader.* Maxwell said of his writings: 'By the study of
Boltzmann I have been unable to understand him. He could not understand me
on account of my shortness, and his length was and is an equal stumbling block
to me' [M3]. Einstein once said to a student of his: 'Boltzmann's work is not easy
to read. There are great physicists who have not understood it' [S6].** That state-
ment was made around 1910, when he was a professor at the University of Zurich.
By then he must have read Boltzmann's major memoir of 1877 on the statistical
mechanical derivation of the second law, since he referred to that paper (for the
first time!) in 1909 [E47]. However, it is very doubtful whether in the years from
1901 to 1904, when he did his own work on this subject, Einstein knew either this
paper or the one of 1868, in which Boltzmann had introduced his first definition
of probability.
It must have been difficult for Einstein to get hold of scientific journals. Recall
that the first of his three papers on the foundations of statistical mechanics was
completed while he was still a teacher at SchafFhausen.t His move to Bern does
not seem to have improved his access to the literature very much [E48]. It is also
unclear whether he had read Maxwell's papers on kinetic theory at that time.
Certainly, he did not know English then, since he did not start to study that lan-
guage until about 1909 [S7] and his knowledge of it was still rudimentary when
he came to the United States.:):
Yet Einstein was acquainted with some of Maxwell's and Boltzmann's achieve-
ments. As he put it in his first paper on statistical physics [E10]: 'Maxwell's and
Boltzmann's theories have already come close to the goal' of deriving the laws of
thermal equilibrium and the second law from the equations of mechanics and the
theory of probability. However, he remarked, this goal had not yet been achieved
and the purpose of his own paper was 'to fill the gap' left by these men. From the
single reference in Einstein's paper, it is clear how much he could have learned
about their work. This reference is to Boltzmann's lectures on gas theory [B15],
a two-volume work which contains much original research and which was cer-
tainly not intended by Boltzmann to be a synopsis of his earlier work. The book
is largely based on the kinetic method (the Boltzmann equation); by comparison,
the comments on the statistical method are quite brief. The counting formula of
complexions is mentioned [B6]; however, said Boltzmann, 'I must content myself
to indicate [this method] only in passing,' and he then concluded this topic with
a reference to his 1877 paper. Also, it seems possible to me that Einstein knew of
*See especially Klein's memoir [K3] for a discussion of Boltzmann's style.
"The encyclopedia article by the Ehrenfests contains several such qualifying phrases as 'The aim
of the. .. investigations by Boltzmann seems to be .. .' [E46].
fSee Chapter 3.|Helen Dukas, private communication. However, it may be that Einstein did see one of the German
translations of Maxwell's Theory of Heat, dating from the 1870s.