This expression became known as the Rayleigh law. Already in 1900 Rubens and
Kurlbaum (and also Lummer and Pringsheim) found this law wanting, as was
seen on page 367.
Thus the experimentalists close to Planck were well aware of Rayleigh's work.
One wonders whether or not Planck himself knew of this important paper, which
appeared half a year before he proposed his own law. Whichever may be the case,
in 1900 Planck did not refer to Rayleigh's contribution.!
March 17 and June 9, 1905. Einstein gives the derivation of Eq. 19.17 dis-
cussed previously. His paper is submitted March 17 and appears on June 9.
May 6 and 18, 1905. In a letter to Nature (published May 18), Rayleigh
returns to his ^T^law and now computes c,. His answer for ct is off by a factor
of 8[R5].
June 5, 1905. James Hopwood Jeans adds a postscript to a completed paper,
in which he corrects Rayleigh's oversight. The paper appears a month later [Jl].
In July 1905 Rayleigh acknowledges Jeans' contribution [R6].
It follows from this chronology (not that it matters much) that the Rayleigh-
Jeans law ought properly to be called the Rayleigh-Einstein-Jeans law.
The purpose of this digression about Eq. 19.17 is not merely to note who said
what first. Of far greater interest is the role this equation played in the early
reactions to the quantum theory. From 1900 to 1905, Planck's radiation formula
was generally considered to be neither more nor less than a successful represen-
tation of the data (see [Bl]). Only in 1905 did it begin to dawn, and then only on
* Planck derived his radiation law in a circuitous way via the equilibrium properties of his material
oscillators. He did so because of his simultaneous concern with two questions, How is radiative
equilibrium established? What is the equilibrium distribution? The introduction of the material
oscillators would, Planck hoped, show the way to answer both questions. Rayleigh wisely concen-
trated on the second question only. He considered a cavity filled with 'aetherial oscillators' assumed
to be in equilibrium. This enabled him to apply equipartition directly to these radiation oscillators.
**This same observation was also made independently by Einstein in 1905 [E5].
fNeither did Lorentz, who in 1903 gave still another derivation of the v^2 T law [L3]. The details
need not concern us. It should be noted that Lorentz gave the correct answer for the constant ct.
However, he did not derive the expression for ct directly. Rather he found c\ by appealing to the
long-wavelength limit of Planck's law.(19.18)
374 THE QUANTUM THEORYdistinct advantage over Planck's reasoning of dispensing altogether with the lat-
ter's material oscillators.* Rayleigh also realizes that this relation should be inter-
preted as a limiting law: 'The suggestion is then that [p = c^T], rather than
[Wien's law, Eq. 19.5] may be the proper form when [ T/v\ is great' (my ital-
ics).** In order to suppress the catastrophic high frequency behavior, he intro-
duces next an ad hoc exponential cutoff factor and proposes the overall radiation
law