title SUMMARY /title The publication of La Corrispondenza di Pietro Mengoli (Florence 1986), for the ' Archives of the Correspondence of Italian Scientists ' edited by the Istituto e Museo di Storia della Scienza, draws attention to a little-known mathematician and natural philosopher of the Galileian School, who was active in Bologna from 1625-1686. Mengoli was trained at the school of Bonaventura Cavalieri (1598-1647), and, after his teacher's death, became professor of mechanics (from 1649-50) and then mathematicis (from 1678 to 1685) in the Bolognese Studium. Today Mengoli's name is known mainly to Italian historians of mathematics interested in his Novae quadraturae arithmeticae (1650) and Geometria (1659). Only recently have his several works on ' mixed mathematics ', metaphysics, cosmology and Biblical chronology come to the attention of scholars. During his lifetime, however, the ' Bolognese Mathematician ' was widely known in Europe, especially in the years 1660-1680. His Speculationi di musica (1670) was eagerly awaited by members of the Royal Society, and was reviewed and partly translated in the Philosophical Transactions (1674). Oldenburg, in his review, pointed out for future historians of musical science the main points of interest of this uncommon musical treatise: 1) the peculiar theory of sound; 2) the refusal of the so-called ' coincidence-theory of consonance '; and, 3) the amazing physiology of hearing, which Mengoli based on his assumption of the existence of two drums in the human ear.