III. EINSTEIN’S QUANTUM THEORY OF RADIATION
Yet the boldness and the difficulties of Thomson’s “ether-string” theory did not deter Einstein[167] in 1905 from making it even more radical. In order to connect it up with some results to which Planck of Berlin had been led in studying the facts of black-body radiation, Einstein assumed that the energy emitted by any radiator not only kept together in bunches or quanta as it traveled through space, as Thomson had assumed it to do, but that a given source could emit and absorb radiant energy only in units which are all exactly equal to
,
being the natural frequency of the emitter and
a constant which is the same for all emitters.
I shall not attempt to present the basis for such an assumption, for, as a matter of fact, it had almost none at the time. But whatever its basis, it enabled Einstein to predict at once that the energy of emission of electrons under the influence of light would be governed by the equation
