First edition, rare, of a work ""considered to be the beginning of modern hydraulics. Its fundamental propositions related the areas of cross sections of a river to the volumes of water passing in a given time. [Castelli] also discussed the relation of velocity and head in flow through an orifice"" (DSB). Castelli ""was the founder of the science of 'running water,' or hydrodynamics, just as Archimedes had been the founder of hydrostatics. For centuries, court engineers had been building aqueducts, diverting rivers, and supplying water to fountains and gardens, without having any real understanding of the factors that affect the rate of flow of water in pipes or river beds. Many engineers thought, for example, that water flowing from a height at point B, down to point A, would flow faster if the route from A to B were direct, rather than stretched out in a long wandering channel. He understood that the height difference of A and B is the only factor that affects the amount of water flow. He also discovered a law, often called the law of continuity, requiring that the cross-sectional area of a river times the water velocity be a constant, so that if the river is constricted (by a narrowing, for example) then the water flow will increase accordingly. And he determined that the height of water flowing in an inclined canal is proportional to the square root of the quantity of water flowing in. He did for water flow what Galileo had already done for balls rolling down planes - discovered the basic mathematical laws that determine the quantity and motion of flowing water. In 1628, Castelli published a book on the subject that he had made his own: 'Della misura dell'acque correnti' ('On the Measure of Running Water'). It is the first book on water flow to have a mathematical basis"" (Linda Hall, Scientist of the Day, Dec. 21, 2012). The engraved title features a bridge on the Tiber, with the tiara and arms of Urban VIIII. Castelli (1578-1643) was Galileo's closest disciple and a major proponent and teacher of Galilean thought. On Galileo's recommendation he became professor of mathematics at the University of Pisa. His students included Bonaventura Cavalieri, Alfonso Borelli and Evangelista Torricelli. It was to Castelli that Galileo wrote on Dec. 21, 1613 arguing that Scripture is an infallible guide to salvation, but it is often silent on matters of science, for which Nature must be our guide. This was the beginning of ""the Galileo affair,"" the twenty-year saga that culminated in Galileo's trial for heresy in 1633. No copy on Rare Book Hub since 1984. Carli & Favaro 171; Cinti 137; Roberts & Trent, pp. 66-67; Riccardi I, 290. 4to (211 x 146 mm), pp. [iv], 59, [1, errata], including engraved title page (no printed title page called for) and engraved Barberini coat-of-arms on sectional title, numerous diagrams in text (contemporary manuscript annotations to p. 48, upper and lower margins of title with old repair, not affecting image). Green leather by...