To understand what precipitation is, it helps to understand the complete hydrological cycle – evaporation, water vapour, convection, condensation, clouds, soil moisture, groundwater and the origin of rivers. To understand these it is necessary to know what the building blocks of matter are, but three thousand years ago none of this was known. In consequence, up to the fifteenth century there were few sound ideas about how the natural world operated. Most of the suggestions were guesses or were based on superstition, religious dogma, legends or myths. Very few observations were made to help form hypotheses and no predictions made that would help confirm a theory. But these ancient views need to be included in a book dealing comprehensively with precipitation, and the first chapter covers the period from 2000 BC up to the seventeenth century AD. The second chapter traces developments over the 300-year period from 1600 to 1900, during which progress accelerated rapidly.

This whole period is also of interest in that it shows how science and rational thought backed by observation, experiment and measurement were rare in antiquity and are still very new to humanity, having started in earnest only a few hundred years ago. This book might, therefore, also be seen as a demonstration and celebration of the progress of the scientific method and of secular thought.