From the Preface;

The notion that light is composed of discrete particles can be traced to Newton’s Optics (Newton, 1952), in which he introduced the term ‘corpuscles’ to describe what we now call ‘particles’. However, the overwhelming evidence in favor of the wave nature of light led to the abandonment of the corpuscular theory for almost two centuries. It was resurrected—in a new form—by Einstein’s 1905 explanation of the photoelectric effect, which reconciled the two views by the assumption that the continuous electromagnetic fields of Maxwell’s theory describe the average behavior of individual particles of light. . At the same time, the early quantum theory and the principle of wave–particle duality were introduced into optics by the Einstein equation, E = n hν, n 1,2,3,... which relates the energy E of the light corpuscle, the frequency ν of the associated electromagnetic wave, and Planck’s constant h...