Light waves, radio waves and photons BY

I N 1900 Planck solved the problem of constructing aformula to represent the distribution in energy of the radiation in a uniform temperature enclosure. The formula he obtained seemed to imply that the exchange of energy between the radiation field and the walls of the enclosure must take place in discrete amounts or quanta, the size of the quantum at the (angular) frequency be ing hw, whe r e tt zz lo-* ’ erg sec. Einstein’s subsequent interpretation of the photoelectric effect (1905) also rested on the assumption that light of (angular) frequency is absorbed by a photosensitive surface in amounts hw. Whether light energy actually travels in the form of bundles or quanta was open to question, but there was no reason to suppose that it does not. In this lecture I want to talk about some of th