Note 5 — § 1. The Emission of a Line Spectrum.

In Planck’s original theory certain other assumptions about the properties of the vibrating systems were used. However, Debye (Ann. d. Phys. xxxiii. p. 1427 (1910)) has shown that it is possible to deduce Planck’s formula of radiation without using any assumption about the vibrators, if it be supposed that energy can be transferred between them and the radiation, only in finite quanta . It may further be remarked that Poincaré (Journ. d. Physique, ii. p. 5 (1912)) has deduced the necessity of assuming that the transference of energy takes place in quanta in order to explain the experimental laws of black radiation.