Francesco Sacredo

Giovanni Francesco Sagredo (1571– 5 March 1620) was a Venetianmathematician and close friend of Galileo, who wrote: Many years ago I was most often to be found in the marvellous city of Venice, in discussions with Signore Giovanni Francesco Sagredo, a man of noble extraction and trenchant wit. [2] He was additionally a friend and correspondent of English scientist William Gilbert.

Sagredo added a scale to Galileo's thermoscope to enable the quantitative measurement of temperature, and produced more convenient portable thermometers. Sagredo additionally discussed with Galileo the possibility of a telescope using a mirror (a reflecting telescope).[3] Galileo honoured him after his death by making him one of the characters in Dialogue Concerning the Two Chief World Systems discussing the Copernican and the Ptolemaictheories of astronomy.[2]

In 1619, Galileo and Sagredo exchanged portraits. There are two existing portraits, in the Zhytomyr Regional Museum and the Ashmolean Museum. They are attributed to the brothers Leandro Bassano and Gerolamo Bassano.

Sagredo died 5 March 1620, leaving his possessions to his brother Zaccaria, who largely disposed of them: Sagredo's collection of letters hasn't been found. Sagredo's letters to Gilbert were destroyed in the Great Fire of London.