Book excerpt: The history of the growth and professionalization of American meteorology and its transformation into a physics- and mathematics-based scientific discipline. For much of the first half of the twentieth century, meteorology was more art than science, dependent on an individual forecaster's lifetime of local experience. In Weather by the Numbers, Kristine Harper tells the story of the transformation of meteorology from a “guessing science” into a sophisticated scientific discipline based on physics and mathematics. What made this possible was the development of the electronic digital computer; earlier attempts at numerical weather prediction had foundered on the human inability to solve nonlinear equations quickly enough for timely forecasting. After World War II, the combination of an expanded observation network developed for military purposes, newly trained meteorologists, savvy about math and physics, and the nascent digital computer created a new way of approaching atmospheric theory and weather forecasting. This transformation of a discipline, Harper writes, was the most important intellectual achievement of twentieth-century meteorology, and paved the way for the growth of computer-assisted modeling in all the sciences.