Discourse on the Tides (Discorso Sul Flusso E Il Reflusso Del Mare) is an essay written by Galileo Galilei in 1616 as a letter to Alessandro Orsini that explains the motion of Earth's tides as a consequence of Earth's rotation and revolution around the sun. Though conclusively misguided and eventually discredited by theories addressing gravity, the essay represents the early lineage of tidal theory.