Mary Somerville (1780-1872) would have been a remarkable woman in any age, but as an acknowledged leading mathematician and astronomer at a time when the education of most women was extremely restricted, her achievement was extraordinary. Laplace famously told her that ‘There have been only three women who have understood me. These are yourself, Mrs Somerville, Caroline Herschel and a Mrs Greig of whom I know nothing.’ Mary Somerville was in fact Mrs Greig. After (as she herself said) translating Laplace’s work ‘from algebra into common language’, she wrote On the Connexion of the Physical Sciences (1834). Her intention was to demonstrate the remarkable tendency of modern scientific discoveries ‘to simplify the laws of nature, and to unite detached branches by general principles.’ This and her next book, the two-volume Physical Geography, also reissued in this series, were enormously influential both within the scientific community and beyond.