Summary Boltzmann's principle is part of classical physics, and one of the corner-stones of Planck's quantum theory. It is shown, why Planck's theory of radiation can be derived from this principle without abandoning classical physics, if due regard is taken of atomism. Finally, there is given an outline of a quantum theory completely based on statistical axioms without any appeal to nonclassical physical principles.

Boltzmann's principle is part of classical physics, and one of the corner-stones of Planck's quantum theory. It is shown, why Planck's theory of radiation can be derived from this principle without abandoning classical physics, if due regard is taken of atomism. Finally, there is given an outline of a quantum theory completely based on statistical axioms without any appeal to nonclassical physical principles.