On the absorption and scattering of light

When a beam of light passes through a material medium it suffers gradual extinction, mainly through molecular scattering, but partly also through conversion into heat. The two processes should be clearly distinguished, as there is some danger of confusing the issue if the term “absorption” is applied to what is a mere diversion of the light energy from its original direction. It is easy enough to form an idea of the mechanism involved in scattering, but the process of absorption is more difficult to represent analytically. In order to obtain a clearer view of its fundamental features, I propose to discuss the transmission of light through a medium the molecules of which have only one free period of vibration.