Galileo's condemnation: The real and complex story

Georgia Journal of Science, 2003 by McMullen, Emerson Thomas

Officially, the Congregation of the Index (or Prohibited Books) ordered corrections to be made to Copernicus' book, and took other actions concerning the matter. This included completely suppressing Carmelite Father Paulo Foscarini's book advocating Copernicanism. However, famous Galileo met with Pope Paul, who assured him that he had not been on trial and not condemned. Later, Galileo asked Bellarmine for a memorandum of the meeting to show that he had not been condemned. This document did not fully enjoin Galileo, but the earlier warning was clear. He followed orders and restrained himself, even though a decree from the Index did not have the weight of one from the pope or a council, such as the Council of Trent.

Comets

In the meantime, Kepler had published on comets (De cometis) and about his third planetary law (Harmonice mundi), both in 1619. Yet Galileo continued to ignore Kepler's revolutionary scientific discoveries, again to his detriment. Galileo's fight over comets was prompted by the publication of a lecture on the subject by another Jesuit, Orazio Grassi.

Grassi, it turns out, was much more correct about comets than Galileo, who had observed only one comet in his life and that was when he was just thirteen years old (26). Later in 1619 Galileo wrote Discourse on Comets in which he argued that comets were purely optical effects due to refractions in the atmosphere. Interestingly, Aristotle also taught that comets were atmospheric phenomena. On the other hand, Grassi supported the view advocated by Tycho Brahe that comets were real phenomena. Further, Brahe's measurements showed cometary paths were beyond the moon's orbit, and Grassi had added to these. In December 1619, Grassi replied to Galileo in The Balance between Astronomy and Philosophy. A battle royal was brewing between the two.

Many in Rome disliked the Jesuits and appealed to Galileo to put them in their place. Among these were Prince Cesi and members of his Academy, who offered to publish whatever Galileo wrote. The hype, the prepublication publicity, and high-level support made Galileo's The Assayer (1623) a success even before it was published (27). The book is well written and a page turner, even if the astronomy is not that good. Again Galileo promoted atomism and discussed the nature of light in it. Just before publication, a friend of Galileo's, Mafeo Barbarini, became Pope Urban VIII and so The Assayer was hurriedly dedicated to him.

Urban

While these events were occurring, Bellarmine died. With that, and the ascension of Urban VIII, Galileo decided to test the waters, so to speak, for another plunge into Copernicanism. The Tuscan Ambassador was correct. Galileo was worked up over the matter and passionately involved in the fight. Comets and atoms would have to wait. Urban VIII was also a Florentine, an admirer of Galileo, and had even written a poem for him (28).

Urban had none of the aversion to Copernicanism that his predecessor had. he seems to have thought that any astronomical theory could never be proven true. He interpreted the decree of the Index to mean that discussion of the earth's motion required special care and diligence (29). He gave Galileo six private audiences in 1624, which naturally included a discussion of the structure of the universe. Urban encouraged Galileo to write about it. Galileo welcomed the opportunity to get back into the battle over Copernicus. The result was the Dialogue on the Two Great World Systems (1632).