The Writing and Publication of the - Dialogue Concerning the Two Chief World Systems.

Following the prohibition of the defense of the Copernican theory in 1616, Galileo refrained from making public reference to the theory for a number of years. After his visit to Rome in 1624, he decided to resume discussion of the issue. The great success of his book The Assayer which was published in Rome in 1623, and of his subsequent visit to Rome, encouraged him to return to the subject.

(The picture is from -The Universe Of Galileo And Newton. By - Bixby, William. 1966, p. 62)

The cardinal of Florence, Maffeo Barberini, who was Galileo's friend and patron, was elected pope, taking the name Urban XIII. The change in Rome following the election of the new pope and the general openness of the Catholic Church to new ideas were, for Galileo, an indication that a book on heliocentric theory might be acceptable to the Church.

Despite its decision to list the heliocentric theory in its Index of Prohibited Books, the Church did not negate all discussions of the heliocentric theory; it only prohibited its defense or acceptance as a true theory of the world. A corrected edition of Copernicus' De Revolutionibus Orbitum, was published in 1620, and an explicit Church edict permitted discussion of this theory as a hypothesis, i.e., as a theory which does not actually claim that the world is constructed thus. Galileo understood that he could discuss this theory from an astronomical and physical point of view so long as his book contained no claim that the earth actually revolved around the sun. For this reason his book does not discuss Scripture, for any interpretation of Scripture according to the Copernican theory, would have indicated that this is a true theory. Following his visit to Rome in the autumn of 1924, Galileo began writing a book on Copernican theory which he called: Dialogue on the Ebb and Flow of the Tides, Which Includes the Implications of the Copernican Theory. In this book he wished to show that from a physical point of view, the Copernican theory is superior to the Ptolemaic (the geocentric) theory and is also capable of explaining the phenomenon of the ebb and flow of the tides.

Galileo finished writing his Dialogue in April 1630, more than five years after beginning it. He took the completed book to Rome to be published. Galileo had a number of practical reasons for publishing the book in Rome, the capital of the Catholic Church, and not elsewhere. Approval of the book by the Roman censorship, would be more powerful than the approval of a local Church censorship such as that of Florence, and would provide better protection against future attacks. His contacts in the highest Church echelons, including the Pope himself, were able to help him get the book published, through personal intervention on his behalf. Galileo also enjoyed the support of the Lycean Academy in Rome, of which he was a member, as well as the support of its head, Prince Ces, who promised Galileo that he would look after publication of his book with one of the Roman book publishers. Galileo probably also preferred to publish his book in the Church's capital, to demonstrate that the Catholic faith does not prohibit discussion of the Copernican theory, although it prohibits upholding the theory or subscribing to it.

However, Galileo encountered difficulties in Rome. Church institutions were not in any rush to publish his book and demanded that a number of corrections be introduced first. Galileo returned to Florence after two months, while his book remained in the hands of the Roman censor, who still worked on a number of final corrections. Ces, who had taken care of the book's publication in Rome, died about a month later. Galileo was unable to return to Rome and attend himself to the publication of the book, because all the roads to Rome were closed due to an epidemic.

(The picture is from - Galileo, Ronan, Colin A. , 1974 , p. 190)

Galileo preferred to publish the book in Florence. It was now necessary to transfer the responsibility for the book's publication from the Roman censorship to the Florentine censorship, not a simple task as the roads were closed and it was not even possible to transfer the entire manuscript. Eventually, the book was approved in Florence in accordance with instructions from Rome.

At the Roman censor's command, Galileo changed the book's name to the name by which it subsequently became known: A Dialogue Concerning the Two Chief World Systems: The Ptolemaic and the Copernican, in order to show that the book presents only a theoretical comparison between the systems. The censor and Galileo formulated an introduction clarifying that the book does not claim that the earth actually moves, but only shows that Copernican claims are more convincing than Aristotelian claims in favor of a stationary earth. However, the religious claim overrules these physical claims. According to the introduction, the book is intended to show that the ruling of the Church against the Copernican theory does not arise from a mistaken understanding of astronomy, but for reasons of faith. At the end of the book, Galileo presents Pope Urban XIII's claim that human understanding is always limited. We can never know things with certainty, and therefore can never prove that observed phenomena necessarily originate from the movement of the earth; hence, despite the fact that the Copernican theory seems more convincing, the earth nevertheless rests at the center of the cosmos, as is known from Scripture. These arguments are not mentioned in the book, only the physical claims in favor of the motion of the earth (see the Dialogue).

The book was approved for publication in Florence in the summer of 1631, about a year after its completion, and was published in February 1632. The book was immediately successful and earned great acclaim following its publication, but together with enthusiasm over the book there were also complaints, and these eventually led to Galileo's trial.

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