The Distant Action of the Heavens in Girolamo Borri’s Tidal Theory

The Aristotelian professor of natural philosophy and courtier at the Medici in Florence, Girolamo Borri, developed a theory based on heat to explain the tidal motions of the sea. In his dialogues on this phenomenon, he deemed that tides follow from the ‘moderate’ simmering of the waters as an effect of lunar light. His tidal theory displaced the theory of the Moon’s distant action on terrestrial waters from its traditionally astrological connotation. Moreover, his theory was not ‘empirical’ but rather inserted in a broad natural philosophical and cosmological framework. Although Galileo Galilei later dismissed heat-based explanations of the tides, such explanations are historically relevant as part of the larger scientific picture, in which controversies over the phenomenon of the tides of the sea fuelled cosmological, even post-Copernican assessments of the connection between terrestrial physics and incipient celestial physics.