Galileo

B

Theory of Tides

Only the Copernican model supported Galileo’s ingenious but mistaken theory of tides. According to Galileo’s theory, the motion of Earth’s rotation is alternately added to Earth’s orbital motion and subtracted from it, with the effect that the seas are set sloshing backward and forward. To this simple mechanism, which provided one tide every 24 hours, Galileo had to add further factors, such as the orientation and configuration of seabeds and shores, to make a reasonable approximation of the variety of tidal phenomena actually observed at different places and seasons.

VI

Galileo and the Inquisition

A Pisan professor, in Galileo’s absence, told the Medici—the ruling family of Florence as well as Galileo’s employers—that belief in a moving Earth was contrary to the Bible. Galileo immediately wrote a pamphlet for private circulation, Letter to Castelli, sketching his views on the relation of scripture and science. In December 1614 a Dominican friar denounced “Galileists” from a Florentine pulpit, and early in 1615 the Florentine Dominican convent of San Marco sent criticisms of Galileists to the Inquisition in Rome.

Galileo enlarged his Letter to Castelli into a Letter to the Grand Duchess Cristina on the correct use of biblical passages in scientific arguments, holding that the interpretation of the Bible should be adapted to increasing knowledge and warning against the danger of treating any scientific opinion as an article of Roman Catholic faith. This remarkable work of amateur theology was not published in Italy in his lifetime and had little influence on the course of events.  

A

The Copernican System and the Church

Early in 1616 Copernican books were subjected to censorship by the church’s Index of Forbidden Books, and Jesuit cardinal Robert Bellarmine instructed Galileo that he must no longer hold or defend the opinion that Earth moves. Following a long tradition that hypotheses in astronomy were merely instruments or calculating devices, Cardinal Bellarmine had previously advised him to treat this subject only hypothetically and for scientific purposes, without taking Copernican concepts as literally true or attempting to reconcile them with the Bible. The ruling of 1616 similarly laid down that Catholics could use Copernicanism as a calculating device but could not say that it was the true system of the universe.

---

---

Galileo remained silent on the subject for years, working on a method of determining longitudes (see Latitude and Longitude) at sea by using his predictions of the positions of Jupiter’s satellites, resuming his earlier studies of falling bodies, and setting forth his views on scientific reasoning in a book on comets, The Assayer, which is a classic of polemical writing.

In 1624 Galileo began a book he wished to call Dialogue on the Tides, in which he discussed the Ptolemaic and Copernican hypotheses in relation to the physics of tides. In 1630 the book was licensed for printing by Roman Catholic censors at Rome, but they altered the title to Dialogue on the Two Chief World Systems. It was published at Florence in 1632. Despite the book’s having two official licenses, Galileo was summoned to Rome by the Inquisition to stand trial for “grave suspicion of heresy.”

B

Galileo’s Trial

Although Galileo had made considerable efforts to conform to the letter of the ruling of 1616, he had clearly written a pro-Copernican book. He had occasionally also slipped up by explicitly treating the Copernican system as “probable,” meaning that, although it was yet unproven, sooner or later it could well be shown to be true. Such a position was incompatible with the ruling of 1616, as was pointed out at his trial: Catholics were allowed to use Copernicanism as a helpful calculating device, provided that they did not treat it as having any truth. 

The charge against Galileo was grounded on a report that Galileo had been personally ordered in 1616 not to discuss Copernicanism either orally or in writing. Cardinal Bellarmine had died, but Galileo produced a certificate signed by the cardinal, stating that Galileo had been subjected to no further restriction than applied to any Roman Catholic under the 1616 edict. No signed document contradicting this was ever found, but Galileo was nevertheless compelled in 1633 to abjure (formally renounce his beliefs) and was sentenced to life imprisonment (swiftly commuted to permanent house arrest). The Dialogue was ordered to be burned, and the sentence against him was to be read publicly in every university.

VII

Galileo’s Impact on Thought

The condemnation of Galileo did have some effect on universities and colleges in countries where the Catholic Church exercised control over teaching and publication, although the permission to treat Copernicanism as a useful, though false, calculating device meant that heliocentric (Sun-centered) ideas could always be made familiar to students. The ideas contained in the Dialogue could not be suppressed, and Galileo’s own scientific reputation remained high, both in Italy and abroad, especially after the publication of his final and greatest work.

Galileo’s final book, Discourses Concerning Two New Sciences, was published at Leiden in 1638. It reviews and refines his earlier studies of motion and, in general, the principles of mechanics. The book opened a road that was to lead Newton to the law of universal gravitation, which linked the planetary laws discovered by Galileo’s contemporary Johannes Kepler with Galileo’s mathematical physics. Galileo became blind before it was published, and he died at Arcetri, near Florence, on January 8, 1642.

Galileo’s most valuable scientific contribution was his part in transforming physics from a plausible framework erected on casual observations of complex everyday experiences into a method whereby selected experiences were so simplified that their underlying structures or patterns could be explained in geometrical terms and thus become susceptible to precise measurement. Galileo’s law of falling bodies, for example, disregards the resistance of the medium and concentrates solely on the relationship between distance fallen and time elapsed in a vacuum. If this simplified law proves to be only approximate, then the approach is repeated to find what refinement is needed to account for how an actual body falls through a medium—for example, through air. 

Galileo abandoned the key Aristotelian ideas according to which rest is a natural state and only motion needs explanation, and got so near to understanding the nature of inertial motion that Newton credited him with the discovery. More widely influential, however, were The Starry Messenger and Dialogue on the Two Chief World Systems, which opened new vistas in astronomy. Galileo was an outstanding popularizer of his own work and is recognized as a master of Italian prose. 

Galileo’s lifelong struggle to free scientific inquiry from restriction by philosophical and theological interference is also remembered as a major contribution to the development of science. Since the full publication of Galileo’s trial documents in the 1870s, entire responsibility for Galileo’s condemnation has customarily been placed on the officials of the Roman Catholic Church. A fuller picture would include the role of the professors of philosophy who first persuaded theologians to link Galileo’s science with heresy, although the responsibility for the ruling of 1616 and for the condemnation of Galileo must remain with the officials of the church and their advisers. 

An investigation into the astronomer’s condemnation was opened in 1979 by Pope John Paul II. A papal commission, set up in 1982, produced several scholarly publications related to the trial. In October 1992 the commission acknowledged the error of the church’s officials. In a speech accepting the report John Paul, alluding to Galileo’s views on scripture and science, said that Galileo, “a sincere believer, showed himself to be more perceptive in this regard than the theologians who opposed him.”

	More from Encarta
	•  7 tips for funding an online degree •  How to succeed in the fashion industry without being a top designer •  Presidential Myths Quiz •  Coffee break: Recharge your brain