SIR CHARLES LYELL (1797-1875), British geologist. Lyell is most famous for his great geological opus: The Principles of Geology: Being an Attempt to Explain the Former Changes of the Earth's Surface, by Reference to Causes now in Operation (3 vols 1830-33). Jim Secord is a lecturer in the Department of History and Philosophy of Science at Cambridge and is the author of Controversy in Victorian Geology (1986).