THE LIGHT-QUANTUM 375a few, that a crisis in physics was at hand [E6]. The failure of the Rayleigh-
Einstein-Jeans law was the cause of this turn of events.
Rayleigh's position on the failure of Eq. 19.17 as a universal law was that 'we
must admit the failure of the law of equipartition in these extreme cases' (i.e., at
high frequencies) [R5]. Jeans took a different view: the equipartition law is cor-
rect but 'the supposition that the energy of the ether is in equilibrium with that
of matter is utterly erroneous in the case of ether vibrations of short wavelength
under experimental conditions' [J2]. Thus Jeans considered Planck's constant h
as a phenomenological parameter well-suited as an aid in fitting data but devoid
of fundamental significance. The nonequilibrium-versus-failure-of-equipartition
debate continued for a number of years [H2]. The issue was still raised at the first
Solvay Congress in 1911, but by then the nonequilibrium view no longer aroused
much interest.The March paper, the first of Einstein's six papers written in 1905, was com-
pleted almost exactly one year after he had finished the single article he published
in 1904 [E7], in which Planck is mentioned for the first time (see Section 4c). The
middle section of that paper is entitled 'On the meaning of the constant K in the
kinetic atomic energy,' K being half the Boltzmann constant. In the final section,
'Application to radiation,' he had discussed energy fluctuations of radiation near
thermal equilibrium. He was on his way from studying the second law of ther-
modynamics to finding methods for the determination of k or—which is almost
the same thing—Avogadro's number N. He was also on his way from statistical
physics to quantum physics. After the 1904 paper came a one-year pause. His
first son was born. His first permanent appointment at the patent office came
through. He thought long and hard in that year, I believe. Then, in Section 2 of
the March paper, he stated the first new method of the many he was to give in
1905 for the determination of N: compare Eq. 19.17 with the long-wavelength
experimental data. This gave him
(19.19)
1 his value is just as good as the one Planck had tound trom his radiation law,
but, Einstein argued, if I use Eq. 19.17 instead of Planck's law (Eq. 19.6), then
I understand from accepted first principles what I am doing.
Einstein derived the above value for N in the light-quantum paper, completed
in March 1905. One month later, in his doctoral thesis, he found N — 2.1 X
1023. He did not point out either that the March value was good or that the April
value left something to be desired, for the simple reason that TV was not known
well at that time. I have already discussed the important role that Einstein's May
1905 method, Brownian motion, played in the consolidation of the value for N.
We now leave the classical part of the March paper and turn to its quantum
part.