The profoundly original ideas introduced by Nobel laureate Max Planck in this endeavor to reconcile the electromagnetic theory of radiation with experimental facts have proved to be of the greatest importance. Few modern introductions to the theory of heat radiation can match this work for precision, care, and attention to details of proof. Although Planck originally intended the book to be simply the connected account of ten years of study, he soon expanded it to a treatise which could serve as an introduction to the study of the entire theory of radiant heat in terms of the recently discovered principle of quantum action. He states his point of view in the introduction: «The hypothesis of quanta … may be reduced to the simple proposition that the thermodynamic probability of a physical state is a definite integral number, or, what amounts to the same thing, that the entropy of a state has quite a definite positive value, which, as a minimum, becomes zero, while in contrast therewith, the energy may, according to the classical thermodynamics, decrease without limit to minus infinity.» Although several other points of fundamental value in thermodynamics are included, the book is basically a rigorous elaboration of this fundamental idea.The treatment starts from the simple known experimental laws of optics and advances, by gradual extension and the addition of the results of electrodynamics and thermodynamics, to the problems of spectral distribution of energy and of reversibility.
