2 6 8 D O C . 2 8 1 R E V I E W P L A N C K

281. Review of Max Planck, Wärmestrahlung

[Einstein 1924h]

Published 5 July 1924

In: Deutsche Literaturzeitung 1 (1924): 1153–1154.

Max Planck [reg. prof. of theor. physics at the Univ. Berlin], Wärmestrahlung. Vorlesungen

über die Theorie der Wärmestrahlung [Heat Radiation. Lectures on the Theory of Heat Ra-

diation], 5th ed., Leipzig, Joh[ann] Ambr[osius] Barth,

1923.[1]

Planck’s book is a clear and methodical introduction to the problems of radiation

and quantum theory, affording an aesthetically highly pleasurable read even for the

initiated.

In the first half of the book, the basic concepts are treated, as are the laws essen-

tially based on thermodynamics, Kirchhoff’s law on emission and absorption, the

Stefan-Boltzmann law on the temperature dependence of total radiation density,

and Wien’s displacement law. The second part of the book is grounded in Boltz-

mann’s principle and quantum theory, where, on one hand, the opposition between

the two theories (classical and quantum theory) is clearly expressed; on the other,

however, is the far-reaching analogy existing between the relations valid for both

theories. Boltzmann’s principle is presented first; it is based on the concept of the

number of complexions, and from the very outset takes into account classical the-

ory and quantum theory through infinitesimals, i.e., finite extension of elementary

domains. Mechanics is used only insofar as the equivalence of the volumes of

phase space corresponding to elementary domains is founded on Liouville’s theo-

rem. That is how Boltzmann’s distribution law, forming the basis of all statistical

heat theory, is based solely on Boltzmann’s principle of entropy probability, which

brings to light its significance that reaches beyond mechanics.

The most important part of the book, pp. 143 to 192, is devoted to the derivation

of Planck’s radiation formula. The train of thought is this: The statistics of ponder-

able structures is determined by Boltzmann’s distribution law. Black-body radia-

tion is defined by it being in statistical equilibrium with these structures. On pp.

143–169 it is demonstrated that one arrives at Jeans’s limiting law if vanishingly

small elementary areas are taken as a basis in Boltzmann’s distribution law, and the

laws of mechanics and electrodynamics are taken as a basis in the interactions be-

tween ponderable structures and radiation. On pp. 169–192, by contrast, Planck’s

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[p. 1154]