Giovanni Francesco Sagredo

Giovanni Francesco Sagredo (1571 to 1620) was a Venetian mathematician and close friend of Galileo, and also a friend and correspondent of the English scientist William Gilbert. He is remembered mainly because he appears as one of the speakers in Galileo's Dialogue Concerning the Two Chief World Systems of 1632. Born into a noble Venetian family, the fourth of six brothers, he became a member of the Great Council of Venice in 1596, at twenty five, and never married. Almost everything known of him comes from about a hundred surviving letters he wrote to Galileo. In the 1590s he studied privately with Galileo, who had come to the University of Padua in 1592, and in 1599 he used his family connections to try to win Galileo a salary increase there. He shared with Galileo and Paolo Sarpi an interest in astronomy and magnetism. By 1600 his name was known to Tycho Brahe, who named him as a contact for copies of star charts offered to the Doge and Senate, and Gilbert described him in a letter as a great magnetical man, since Gilbert's work raised the hope of mapping magnetic declination to help solve the problem of longitude.