Magnetism for Librarians. Leone Allacci’s De Magnete (1625) and its Relation to Giulio Cesare LaGalla’s Disputatio de Sympathia et Antipathia (1623)

The investigation of magnetic phenomena played a crucial role for the emergence of an experimental approach to natural philosophy in the early modern period. William Gilbert’s De magnete, in particular, and Leonardo Garzoni’s Due trattati, are taken to herald this development. This article brings to light a contrasting approach to magnetism, by analyzing an extensive and hitherto unknown study on the magnet by the Vatican librarian Leone Allacci, and its relation to Giulio Cesare LaGalla’s Disputatio de sympathia et antipathia (1623). Allacci’s De magnete (1625) which survives in a single manuscript, offers a comprehensive literature review on early modern knowledge about the magnet in a variety of disciplines, including natural history, natural philosophy, navigational science, natural magic, and medicine. Allacci incorporates Greek Byzantine authors as well into his doxographical anthology, and he commends the Paracelsian ‘weapon salve,’ which was condemned by most Catholics at his time.