James Croll (1821-90) was self-educated, but on gaining a post at the Glagow Andersonian Museum had the time to explore his academic interests. Despite his lack of formal training, he quickly became a leading light of the Scottish Royal Geological Society. Using physics, mathematics, geology and geography he explored the pressing scientific questions of the time. In this, his final book, published in 1889, Croll divides his focus between 'the probable origin of meteorites, comets and nebulae', the age of the sun and the impact of the pre-nebular condition of the universe on star evolution. Using both proven facts and theories, Croll explores the ideas and hypotheses then current, frequently crediting colleagues for their work, and building on it. Croll, who from humble beginnings became a Fellow of The Royal Society and of St Andrew's University, writes in a style which makes his works accessible to a lay readership.