Cesare Marsili

Cesare Marsili (Bologna, 31 January 1592 - Bologna, March 22, 1633) was an Italian intellectual and associate of Galileo Galilei.

Cesare Marsili was born into one of the most important senatorial families of the city, the son of Filippo Marsili and Elizabetta Rossi. From an early age he assumed various positions of authority in the city, becoming a member of the Council of Elders, tribune of the people, standard-bearer of justice. In 1622, just thirty years old, was elected Superintendent of Water, a position which he required hydraulic and mathematical skills that he had probably learned from Giovanni Antonio Magini, professor of mathematics and astronomy University of Bologna. On 10 November 1628, he married a noblewoman named Elena Ballatini.

An efficient government man, an educated scholar, Marsili was a member of several academies, including the Gelati, the Notte and the Torbidi. In 1624 he went to Rome following the election of Pope Urban VIII and there he met Galileo Galilei, through whom he became a member of the Accademia dei Lincei in 1625. Galileo had had a close friendship with Filippo Salviati for many years, and since his early death had lacked a close confidant. Marsili quickly came to fill this role for him. Marsili was also an enthusiastic jouster and is known to have participated a number of tournaments between 1615 and 1628.

Marsili's friendship with Galileo and the extensive correspondence between them cast light on the nature of Galileos' work and the activities of the Accademia dei Lincei. Because of his social standing, he was a vital link between Galileo and the political elites in Rome and Bologna. From this correspondence emerges Marsili's passion for experiments and measuring instruments, to which he devoted his own studies and activities. On one occasion, we know that Galileo send him two top-quality telescope lenses, and promised him a telescope in due course.

The letters also provide insight into otherwise unknown experiments. In April 1626, after learning from Marsili that "a certain engineer" in Bologna had built a device that imitated the motion of the tides, Galileo responded that he had made a similar machine himself twenty years previously, but that it had not been for studying the tides. Galileo's accounts indicate that he had a clear idea of the principles of the thermometer by around 1606-08, so the claim to have invented it properly belong to him. In another letter of 7 July 1626, Marsili reported that a Bolognese artisan had succeeded in manufacturing a mirror that could produce the effects of a telescope, but that it had not yet been possible for him to verify its working. As the correspondence continued, it was clear that Marsili and Galileo were developing the concept of the reflecting telescope, an idea that was to be developed by Cavalieri.

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