The comets and the method
The three comets that appeared between 1618 and 1619 gave rise to another heated argument, this time between Galileo and the Jesuit priest Orazio Grassi. By now, however, Galileo had been silenced by a pronouncement of the Holy Office, which had suspended Copernicus’s De revolutionibus in 1616, admitting the theory of the Earth’s mobility only as a mathematical hypothesis, not to be proclaimed as a natural truth, because contrary to Holy Scripture. Consequently, Galileo could make no effective response to Grassi, who had adopted Tycho Brahe’s geo-heliocentric theory, after Galileo’s astronomical discoveries had demonstrated the erroneous nature of the Ptolemaic system. Il saggiatore [The Assayer] - the most salient moment of the dispute on comets, the nature of which had not been fully understood by Galileo who believed that they were vapors from the Earth condensed in the cosmic space - is a milestone in methodology. Moreover, it proposes a new scale of values for natural philosophy, where authority and tradition, literature and books, are deemed infinitely less important that studying the world and the mathematical laws that govern it.