Giovanni Francesco Sagredo

Giovanni Francesco Sagredo (19 June 1571 – 5 March 1620) was a Venetian mathematician and close friend of Galileo. He was also a friend and correspondent of English scientist William Gilbert. He is remembered today mainly because he appears as one of the figures in Galileo's controversial work the Dialogue Concerning the Two Chief World Systems.

Family background Sagredo was the fourth of six brothers born to Nicolò Sagredo, son of Bernardo of the S. Sofia branch of the family, and his wife Cecilia, daughter of Paolo Tiepolo. The Sagredo family traced its roots back to the fifth century. His grandfather Bernardo was procurator of S. Marco, while his father, who died in 1615, was appointed administrator of Palmanova in 1600, administrator of Cyprus in 1605, procurator of S. Marco in 1611 and reformer of the University of Padua in 1613. The family lived mainly in Palazzo Sagredo, near the Venetian arsenal and the family church of San Francesco della Vigna, but also owned extensive land holdings in the mainland and elsewhere, including a palace in (it) Marocco and beech forests with iron mines near Cadore.

Giovanni Francesco himself did not marry and had no children. He became a member of the Great Council of Venice in 1596 at the age of 25.

Early studies and magnetism Almost everything known of Sagredo is based on the letters that he wrote to Galileo Galilei. About a hundred survive, although those written by Galilei to him are lost. In the 1590s Sagredo studied privately with Galileo, who had come to the University of Padua in 1592. In 1599 Sagredo apologized to Galileo for failure to secure a salary increase for him from the university, although he had used his influential family connections to argue his case. In 1602 Galileo drew up a horoscope for Sagredo, which describes him as "blandum, laetum, hilarem, beneficum, pacificum, sociabilem, pronum ad voluptates, Dei amatorem, laborum impatientem" (kind, happy, merry, beneficient, pacific, sociable pleasure-loving, a lover of God, and impatient of troubles).

Sagredo shared an interest in both astronomy and magnetism with Galileo and Paolo Sarpi. By 1600 Sagredo's name was known to Tycho Brahe, who in a letter to Gian Vincenzo Pinelli referred to him as a good contact for the two copies of the star charts that Tycho had offered to the Doge and Senate. Another letter, to William Gilbert describes Sagredo as a "great Magneticall man".

Opposing the Jesuits In April 1606 escalating disputes between Venice and the Vatican led Pope Paul V to decree the Venetian Interdict and Doge Leonardo Donato to expel the Jesuits from the Republic. Shortly afterwards in August 1606 Sagredo was appointed treasurer of the fortress of Palmanova. The Interdict was revoked in April 1607, Sagredo returned to Venice in May and in November he was appointed consul in Syria. That his underlying attitude towards the Jesuits was unchanged is shown by a letter he sent to Sarpi on 30 April 1609 describing how the world was gradually falling prey to them, especially in eastern India and Japan. In this capacity he was visited by one Xwāje Ṣafar, an Armenian merchant traveling to Venice on behalf of Shah Abbas, who carried with him the correspondence from the Carmelites of Isfahan. This included sensitive military information sent by the viceroy of India to Philip III of Spain. Another file contained details of the negotiations between Abbas and Philip for the drafting of an anti-Ottoman treaty, which would have had an impact on Venetian access to Persian silk. Sagredo took these documents and copied them, earning him a reprimand from the Council of Ten and probably hastening the end of his diplomatic career. and in 1613 he began a two-year service as one of the , Venice's Board of Trade. and produced more convenient portable thermometers. Sagredo also discussed with Galileo the possibility of a telescope using a mirror (a reflecting telescope).

In June 1619, Galileo and Sagredo exchanged portraits. Sagredo's portrait was by Leandro Bassano. The portrait represents him with his commission from the Doge in front of him on a kilim which was a gift from Abbas I in exchange for the offer of scientific instruments. The portrait, currently in the Ashmolean Museum and the other in a private collection.

Death Sagredo died on 5 March 1620 and his last confession was heard by Sarpi. He was buried near his father in the family crypt in S. Francesco della Vigna. His possessions passed to his brother Zaccaria who disposed of all his scientific instruments and his collection of letters has not been found. Sagredo's letters to Gilbert were destroyed in the Great Fire of London.