The theory put forward by the writer to explain the emission of a line-spectrum may be summarized as follows:—
The principal assumption of Planck’s theory is that the energy of a system of vibrating electrified particles cannot be transferred into radiation, and vice versa, in the continuous way assumed in the ordinary electrodynamics, but only in finite quanta of the amount
, where
is a universal constant and
the frequency of the radiation[5]. Applying this assumption to the emission of a line-spectrum, and assuming that a certain spectral line of frequency
corresponds to a radiation emitted during the transition of an elementary system from a state in which its energy is