During the final year of his life, Galileo recommended to his correspondents – mathematicians such as Renieri and Cavalieri, but also sophisticated laymen such as Micanzio and Rinuccini – to read Giovanni Nardi‘s De igne subterraneo (1641), a book he regarded as deserving scrutiny and discussion. After presenting Nardi’s ideas, the likely reasons of Galileo’s interest will be explored with regard to his work on sunspots and comets but also on the matter theory and his relations with the natural history studies of the Lincean Academy. This episode shows that, although he could not devote time to that topic, Galileo was well aware that a new theory of the earth as part of a new sublunary physics was a necessary consequence of accepting the Copernican cosmology and that such theory should be based on a corpuscular conception of matter radically different from the elemental theory of Aristotle.
