The cause of the ice ages was a puzzle to nineteenth-century climatologists. One of the most popular theories was that the affected continents must somehow have been hugely elevated and, like mountains, iced over. However, in this 1885 study of the problem, James Croll (1821 90) argues that such staggering movement would have been impossible. Instead, he puts forward a new theory: that the eccentricity of the earth's orbit changes at regular intervals over long periods, creating 'great secular summers and winters'. Adopting a meticulous approach to the facts, he disproves a host of...