This book is addressed to those who wish to understand the relationship between atmospheric phenomena and the nature of matter as expressed in the principles of physics. The interesting atmospheric phenomena are more than applications of gravitation, of thermodynamics, of hydrodynamics, or of electrodynamics; and mastery of the results of controlled experiment and of the related theory alone does not imply an understanding of atmospheric phenomena. This distinction arises because the extent and the complexity of the atmosphere permit effects and interactions that are entirely negligible in the laboratory or are deliberately excluded from it. the objective of laboratory physics is, by isolating the relevant variables, to reveal the fundamental properties of matter; whereas the objective of atmospheric physics, or of any observational science, is to understand those phenomena that are characteristic of the whole system. For these reasons the exposition of atmospheric physics requires substantial extensions of classical physics. It also requires that understanding be based on a coherent way of seeing the ensemble of atmospheric phenomena. Only then is understanding likely to stimulate still more general insights.