1578-1643

Italian astronomer and hydrologist whose pioneering work Della misura dell'acque correnti (1628) marks the beginning of modern hydraulics. Castelli related river cross-sectional areas to the water volume passing through those areas and discussed the relation of velocity to head in flow through an orifice. In a celebrated series of letters to Galileo (1637-1638), he discussed absorption of radiant heat by black and white objects. A loyal supporter of Galileo, Castelli played an important role in extending and transmitting his work.