The Essential Galileo (3 page)

The Assayer
is written in the form of a letter to Virginio Cesarini (1595–1624), chamberlain to Pope Urban VIII, member of the Lincean Academy, poet, and friend of Galileo's. Additionally, it is structured as a series of long quotations from the
Balance
, each followed by a lengthy critical analysis. The controversy with Grassi did not end then, for in 1626 the latter published in Paris an even more voluminous work entitled
Comparison of the Weights of the Assayer and the Balance
. However, Galileo felt no need for a further reply.

There were several astronomical and philosophical issues underlying this controversy. One was whether comets were located in the earth's atmosphere (as Aristotle had claimed) or in the heavens (as Tycho Brahe had argued based on his study of the comet of 1577). A related question was whether or not the heavenly location of comets implied the existence of heavenly changes and so further undermined the earth-heaven dichotomy. Another issue was whether the precise trajectory followed by the third comet of 1618 could be explained in a geostatic geocentric theory, or whether the explanation had to include the Copernican hypothesis that the earth possesses an annual heliocentric motion. There was also the question whether the Tychonic system of the world was correct; this was the arrangement according to which the planets do revolve around the sun, but the sun (together with the planetary system) revolves both diurnally and annually around the motionless central earth. And there were more general issues: whether natural science should try to reduce secondary qualities, e.g., colors and sounds, to primary qualities, e.g., position and motion (as the corpuscular or atomistic worldview claimed); and what is the relative role of authority and independentmindedness in scientific inquiry. Galileo and Grassi disagreed on almost all these questions. Even when they happened to agree (e.g., on the heavenly location of comets), they disagreed about the manner of arriving at the conclusion.

Galileo's
The Assayer
is thus not only an explicit discussion of comets and scientific method and an explicit critique of the Tychonic system, but also an implicit defense of the banned Copernican system.

[§0.9] The election of Barberini as Pope Urban VIII, and his enthusiasm for
The Assayer
, encouraged Galileo to pursue the Copernican research program. So Galileo went to work to write the book on the system of the world which he had conceived earlier and to adapt its form to the new restrictions.

Thus, he wrote the book in the form of a dialogue among three characters who discuss all the cosmological, astronomical, physical, and epistemological arguments on both sides of the questions; but no biblical or theological arguments are critically examined. This
Dialogue
was published in 1632 in Florence, and its key thesis is best stated as follows: the arguments and evidence in favor of the geokinetic theory are much stronger that those in favor of the geostatic view, and in that sense the earth's motion is much more probable than geostaticism. When so stated, the thesis is successfully established. In the process, Galileo managed to incorporate into the discussion the new telescopic discoveries, his conclusions about the physics of moving bodies, a geokinetic explanation of the tides, and various methodological reflections. From the viewpoint of the ecclesiastic restrictions, Galileo must have felt that the book did not “hold” the theory of the earth's motion because it was not claiming that the geokinetic arguments were conclusive; that it was not “defending” the geokinetic theory because it was merely a critical examination of the arguments on both sides; and that it was a hypothetical discussion because the earth's motion was being presented as a hypothesis that happened to be better than the alternative.

However, Galileo's enemies raised all kinds of charges against the book. One was that the book did not treat the earth's motion as a hypothesis, because it did not regard it merely as a convenient instrument of calculation and prediction, but also as a real possibility; that is, the proposition that the earth moves was regarded as a description of physical reality that could be true or false, even if one could not yet be sure as to which was the case. Another charge was that the book defended the earth's motion because the arguments against it were criticized but the arguments for it were favorably presented. Both of these points involved an alleged violation of the decree of the Index and of Bellarmine's warning. But there was a third charge: that the book violated a special injunction which Galileo had been given in 1616 and which prohibited him from discussing the earth's motion in any way whatsoever; a document reporting on this special injunction had been found in the file of the earlier Inquisition proceedings of 1615–16. Thus Galileo was summoned to Rome to stand trial.

After various delays, Galileo finally arrived in Rome in February 1633, although the proceedings did not begin until April. At the first hearing, Galileo was asked about the
Dialogue
and the events of 1616. He admitted receiving from Bellarmine the warning that the earth's motion could not be held or defended, but only discussed hypothetically. He denied receiving a special injunction not to discuss the topic “in any way whatever,” and in his defense he introduced a certificate he had obtained from Bellarmine in 1616, which only mentioned the prohibition to hold or defend. Galileo also claimed that the book did not defend the earth's motion, but rather suggested that the favorable arguments were inconclusive, and so did not violate Bellarmine's warning.

The special injunction must have surprised Galileo as much as Bel-larmine's certificate did the inquisitors. In fact, it took three weeks before they decided on the next step. The inquisitors opted for some out-of-court plea bargaining: they would not press the most serious but most questionable charge (violation of the special injunction), but Galileo would have to plead guilty to a lesser but more provable charge (transgression of the warning not to defend Copernicanism). He requested a few days to devise a dignified way of pleading guilty to the lesser charge. Thus, at later hearings, he stated that the first deposition had prompted him to reread his book; he was surprised to find that it gave readers the impression that the author was defending the earth's motion, even though this had not been his intention. He attributed his error to wanting to appear clever by making the weaker side look stronger. He was sorry and ready to make amends.

Although the authorities accepted this confession of guilt, they were unsure about Galileo's denial of a malicious intention. Thus, in accordance with standard practice, they decided to subject him to an interrogation under the verbal threat of torture. This occurred on June 21, and the transcript indicates that Galileo was threatened with torture but was not actually tortured, and that he was willing to be tortured rather than admit his transgression to have been intentional (thus vindicating the purity of his intention).

The trial ended on 22 June 1633 with a harsher sentence than Galileo had been led to believe he would receive. The verdict found him guilty of a category of heresy intermediate between the most and the least serious, called “vehement suspicion of heresy”; the objectionable beliefs were the cosmological thesis that the earth moves and the methodological principle that the Bible is not a scientific authority. Thus he was forced to recite a humiliating “abjuration.” And the
Dialogue
was banned.

The sentence also states that he was to be held in prison indefinitely. However, this particular penalty was immediately commuted to house arrest. Accordingly, for about one week he was confined to the Villa Medici, a sumptuous palace in Rome belonging to the Tuscan grand duke. Then for about five months he was sent to the residence of Siena's archbishop, who was a good friend of Galileo's. Finally, in December 1633 he was allowed to live in seclusion at his own villa in Arcetri, near Florence.

One of the ironic results of this condemnation was that, to keep his sanity, Galileo went back to his earlier research on motion, organized his notes, and five years later published his most important contribution to physics, the
Two New Sciences
(1638). Without the tragedy of the trial, he might have never done it. This book was written in the form of a dialogue among the same characters (Salviati, Sagredo, and Simplicio) who appeared in the earlier
Dialogue
, with the addition that at various points in the discussion Salviati reads from the manuscript of a treatise on motion written by a so-called Academician; this is a reference to Galileo himself, who was proud of being a member of the Lincean Academy.

Galileo died in Arcetri in 1642, assisted and surrounded by his son Vincenzio and his disciples Vincenzio Vivani and Evangelista Torricelli.

1.
Einstein 1954, 271; Hawking 1988, 179; 1992, xvii.

2.
Here I am adapting Gingerich's (1982) eloquent formulation.

3.
Here, I overlook a fourth aspect, which cannot be appreciated in translation. That is, Galileo also happened to be one of the greatest writers in the (800-year) history of the Italian language, and his writings can be appreciated from the literary and aesthetic point of view.

4.
For more details on this controversy, see Drake 1978, 169–79, and 1981; Biagioli 1993, 159–209; Camerota 2004, 227–38.

5.
Galilei 1890–1909, 4: 35; cf. Camerota 2004, 230.

6.
For more details on the sunspots controversy, see Drake 1978, 179–213; Camerota 2004, 238–59; Biagioli 2006, 135–217; Reeves and van Helden forthcoming.

7.
For more details on the comets controversy, see Drake and O'Malley 1960; Drake 1978, 263–88; Biagioli 1993, 267–312; Camerota 2004, 363–98.

Chronology of Galileo's Career and Aftermath