To those of us who take delight in a physical interpretation of the various forms of water manifest in Nature, the process of change of state is, perhaps, the most interesting. The initiation of one phase in another, for example cloud drops or snow crystals from the vapour, ice from the liquid, or Tyndall flowers from the solid occurs either at small centres formed by random molecular motion, or at small foreign particles which happen to be present. It is possible, in principle, to describe these events in thermodynamic terms providing we introduce the interfacial tension and surface area as functions of state. In the first six chapters of this book the authors discuss this thermodynamic formalism in some detail. This is followed by three chapters concerned with the conditions under which drops of water, aqueous solutions and ice crystals can be in equilibrium. The book concludes with a discussion of the theory of homogeneous nucleation of water drops and ice crystals, and its comparison with experiment.

In as far as the book is concerned with equilibrium conditions and homogeneous nucleation, it has a somewhat limited interest for those concerned with real clouds, which form under conditions which are often far from equilibrium, and where nucleation processes may be dominated by the presence of foreign particles of variable concentration. Sufficient effort has not been given to a critical appraisal either of the thermodynamic approach itself, or of the experimental evidence in the section on nucleation—which is a field notorious for spurious results. As a result this book will probably appeal only to a small number of specialists in the field.