Lewis Fry Richardson (1881–1953) became interested in computational mathematics while the subject was still in its infancy. He was a pioneer in numerical analysis, which for our purposes means using arithmetic intelligently to find approximate solutions to mathematical problems that are too complicated to solve exactly. He tried to work out a mathematical system for predicting the weather. He started by doing theoretical meteorology, deriving equations representing the physical laws that describe the evolution of the familiar meteorological properties such as wind, temperature, pressure, and humidity. Richardson’s first numerical weather forecast, obtained after a great deal of tedious calculating, was not very accurate. In fact, it was wildly inaccurate. But Richardson was ahead of his time. He was a visionary. In the late 1940s, a team of meteorologists and mathematicians using one of the earliest computers produced the first successful numerical weather prediction. By the 1950s, routine weather forecasts were being produced by techniques based closely on Richardson’s method.