The next great advance was due to Einstein. He noticed that the well-known anomalies in the specific heats of bodies at very low temperatures could be explained, provided we assumed the discontinuity of energy. As applied to solids, this would connote that the vibrating systems could take up or emit energy only in definite quanta; and, as applied to gases, we should have to assume that the molecules could rotate only with definite frequencies. All these problems dealing with specific heats bring us into contact with the kinetic theory of gases, as also with other realms of physics, such as the problems of anomalous dispersion and selective reflection in optics. Again basing his deductions on the existence of quantum phenomena, Einstein deduced a formula for the photo-electric effect, and this formula was found to be in harmony with experiment. Finally, we may mention that Bohr’s atom, which is also based on the same idea of discontinuity, allowed him to account for certain spectral series.
We now get to the important point. From the expression for the atom of energy or quantum
, where
is a constant and
is the frequency of the radiation, it is obvious that there exist as many different types of quanta of energy as there exist different frequencies of radiation. There is no one unique type of quantum of energy in nature. That which is universal is not the quantum of energy
, but the constant