Series editor David Pines has selected, from the more than one hundred recorded lectures, the six that address the greatest physics discoveries of the past five hundred years. In these lectures, Feynman not only explains gravity, relativity, probability, electromagnetism, quantum mechanics, and superconductivity, he offers his own unique take on what made these discoveries possible. This is a wonderful opportunity to hear Feynman expound on the contributions that have led to our present understanding of the nature of the universe. Volume 19 (Masers and Light) contains sections on polarization and the Principle of Least Action.