THE LIGHT-QUANTUM 373later. It also deals with the quantum theory. It has one thing in common with the
opening sentence mentioned above. They both express Einstein's view that the
quantum theory is provisional in nature. The persistence of this opinion of Ein-
stein's is one of the main themes of this book. Whatever one may think of the
status of the quantum theory in 1955, in 1905 this opinion was, of course, entirely
justified.
In the March paper, Einstein referred to Eq. 19.6 as 'the Planck formula,
which agrees with all experiments to date.' But what was the meaning of Planck's
derivation of that equation? 'The imperfections of [that derivation] remained at
first hidden, which was most fortunate for the development of physics' [E3]. The
March paper opens with a section entitled 'on a difficulty concerning the theory
of blackbody radiation,' in which he put these imperfections in sharp focus.
His very simple argument was based on two solid consequences of classical
theory. The first of these was the Planck equation (Eq. 19.11). The second was
the equipartition law of classical mechanics. Applied to f/in Eq. (19.11), that is,
to the equilibrium energy of a one-dimensional material harmonic oscillator, this
law yields
(19.16)
where R is the gas constant, N Avogadro's number, and R/N (= k) the Boltz-
mann constant (for a number of years, Einstein did not use the symbol k in his
papers). From Eqs. 19.10 and 19.16, Einstein obtained^ T i-.and went on to note that this classical relation is in disagreement with experiment
and has the disastrous consequence that a = oo, where a is the Stefan-Boltzmann
constant given in Eq. 19.3.
'If Planck had drawn this conclusion, he would probably not have made his
great discovery,' Einstein said later [E3]. Planck had obtained Eq. 19.11 in 1897.
At that time, the equipartition law had been known for almost thirty years. Dur-
ing the 1890s, Planck had made several errors in reasoning before he arrived at
his radiation law, but none as astounding and of as great an historical significance
as his fortunate failure to be the first to derive Eq. 19.17. This omission is no
doubt related to Planck's decidedly negative attitude (before 1900) towards Boltz-
mann's ideas on statistical mechanics.
Equation 19.17, commonly known as the Rayleigh-Jeans law, has an inter-
esting and rather hilarious history, as may be seen from the following chronology
of events.
June 1900. There appears a brief paper by Rayleigh [R4]. It contains for the
first time the suggestion to apply to radiation 'the Maxwell -Boltzmann doctrine
of the partition of energy' (i.e., the equipartition theorem). From this doctrine,
Rayleigh goes on to derive the relation p = c^v^2 T but does not evaluate the con-. slant c,. It should be stressed that Rayleigh's derivation of this result had the