An annotated translation of Jean Fernel's "On the Hidden Causes of Things" (1542). A major innovatory work in Renaissance natural philosophy and medicine, and a crucially important source for understanding the notion of occult qualities, with a scholarly introduction.

John M. Forrester retired from a medical career in 1988. He has previously published a translation of Fernel's Physiologia of 1567 (Transaction of the American Philosophical Society, 2003).
John Henry, Ph.D. (1983) is Reader in History of Science at Edinburgh University, and has published widely on Renaissance and early modern science.