William Gilbert (1544-1603), a founder of early modern science in Britain, was the author of De magnete (On the Magnet, 1600), esteemed by many later natural philosophers for its rejection of scholasticism and extensive use of experiment. Since the 19th century, Gilbert has been routinely celebrated as having discovered the fundamental laws of magnetism. In De magnete, he reviews preexisting works, giving slight notice to one Peter Peregrinus (13th c.). In fact, Peregrinus wrote a remarkable tract, Epistola de Magnete (ca. 1268), detailing experiments on magnetic behavior and proposing the earliest dry compass. Over 30 copies are known, including a printed version, testifying to long-term use. Close comparison with De magnete shows beyond doubt that Gilbert plagiarized substantial parts of Peregrinus’ work. Though Gilbert’s Latin is not identical, the methods and materials, order of experiments, and derived “laws” all copy Peregrinus. Why Gilbert believed this would go unnoticed is unclear. Such an episode, however, is important for other reasons. It provides new support for direct connections between medieval and early modern science, an area of some debate. It also poses questions about what constituted “misconduct” at the time and whether similar examples of “borrowing” might have played a larger role in 17th century science.
