The Essential Galileo (2 page)

[§0.6] At about the same time that Galileo was studying and disputing about bodies in water, he was also studying and disputing about sunspots.
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It is uncertain when Galileo first observed sunspots with the telescope, but it is certain that while in Rome in the spring of 1611 he showed them to a number of people. It is also clear that he did not publish or write anything on the topic until stimulated by German Jesuit Christoph Scheiner (1573–1650).

In November and December 1611, Scheiner wrote three letters about sunspots to Marc Welser, an official of the German city of Augsburg. These were published under the pseudonym of Apelles in January 1612 in a small book entitled
Three Letters on Sunspots
. Welser immediately sent Galileo a copy, requesting his opinion. In May, Galileo replied with a long letter to Welser, criticizing Scheiner's views and observations and advancing his own. A second Galilean letter to Welser followed in August. In the meantime, after reading Galileo's first letter, Scheiner wrote another essay, which he published in September under the same pseudonym and with the title
A More Accurate Inquiry on Sunspots
. Galileo again received a copy from Welser and then in December wrote him a third long letter. Finally, in March 1613 the Lincean Academy published in Rome a volume containing Galileo's three letters and an appendix with Scheiner's two booklets. Such was the origin of Galileo's
History and Demonstrations Concerning Sunspots
.

Part of the dispute between Scheiner and Galileo involved priority of discovery. In 1612–13, this aspect of the controversy was relatively subdued, and the most sensible thing to say is that the phenomenon was discovered independently by both. Later, the priority dispute became bitter and nasty, as it came to encompass other aspects of the phenomenon (such as the inclination of the solar axis of rotation) and other more general issues (such as the Copernican controversy). However, the most significant intellectual aspect of the controversy between Galileo and Scheiner concerned the interpretation of the sunspots and their implications for the Copernican theory. Echoes of, and new twists on, the sunspot controversy can be found in almost all of Scheiner's and Galileo's subsequent writings.

In the 1612–13 discussions, Scheiner held that sunspots were swarms of small planets orbiting the sun at small distances. Individually they were invisible; but when several simultaneously reached the line of sight (of an observer from earth), then they appeared as dark spots projected onto the sun. Scheiner's interpretation saved an essential part of the Aristotelian worldview, namely, the earth-heaven dichotomy; according to this doctrine heavenly bodies and terrestrial bodies were very different, insofar as only the latter were subject to physical changes, such as generation and destruction. For Scheiner the only novelty required by sunspots was the existence of some previously unknown planets.

On the other hand, Galileo's interpretation was that sunspots were phenomena occurring on the body of the sun, individually subject to sporadic production and dissolution, but collectively undergoing regular eastward motion. This implied that the sun rotates on its axis (with a period of about one month), and that it undergoes physical changes similar to those on earth (sunspots being analogous to terrestrial clouds). And this in turn undermined a key tenet of the Aristotelian worldview—the earth-heaven dichotomy.

[§0.7] As it became known that Galileo was convinced that the new telescopic evidence rendered the Copernican theory of the earth's motion a serious contender for real physical truth, he came increasingly under attack from conservative philosophers and clergymen in Florence. They started arguing that Galileo was a heretic because he believed in the earth's motion and the earth's motion contradicted the Bible. Underlying this personal attack was the biblical argument against Copernicanism: the earth cannot move, because many biblical passages state or imply that it stands still, and the Bible cannot err. The most frequently mentioned biblical passage was Joshua 10:12–13 (King James Version): “Then spake Joshua to the Lord in the day when the Lord delivered up the Amorites before the children of Israel, and he said in the sight of Israel, ‘Sun, stand thou still upon Gibeon; and thou, Moon, in the valley of Ajalon.' And the sun stood still, and the moon staid, until the people had avenged themselves upon their enemies. Is not this written in the book of Jasher? So the sun stood still in the midst of heaven, and hasteth not to go down about a whole day.”

Although Galileo was aware of the potentially explosive nature of this particular issue, he felt he could not remain silent, but decided to refute the argument. Because of the circumstances of the attacks and to avoid scandalous publicity, he wrote his criticism in the form of long private letters, in December 1613 to his former student Benedetto Castelli, a Benedictine monk and professor of mathematics at Pisa, and in spring 1615 to the grand duchess dowager Christina.

Galileo's critique may be summarized as follows. The biblical argument attempts to prove a conclusion (the earth's rest) on the basis of a premise (the Bible's commitment to the geostatic system) that can only be ascertained with a knowledge of that conclusion in the first place. In fact, the interpretation of the Bible is a serious business, and normally the proper meaning of its statements about natural phenomena can be determined only after we know what is true in nature; thus, the business of biblical interpretation is dependent on physical investigation, and to base a controversial physical conclusion on the Bible is to put the cart before the horse. Second, the biblical objection is a non sequitur, since the Bible is an authority only in matters of faith and morals, not in scientific ones; thus, its saying something about a natural phenomenon does not make it so, and therefore its statements do not constitute valid reasons for drawing corresponding scientific conclusions. Finally, it is questionable whether the earth's motion really contradicts the Bible, as one can show by an analysis of the passage (Joshua 10:12–13) where God stopped the sun to prolong daylight and give Joshua enough time to win a battle before nighttime; according to Galileo, a careful analysis shows that this passage cannot be easily interpreted in accordance with the geostatic theory, but that it accords better with the geokinetic view, especially as improved by Galileo's own discovery of solar axial rotation. The biblical objection is therefore groundless, aside from its other flaws.

Galileo's letter to Castelli was widely circulated, and the conservatives got increasingly upset. The situation was exacerbated in January 1615 when Galileo received the unexpected but welcome support of a Carmelite friar named Paolo Antonio Foscarini, who published a book entitled
Letter on the Opinion, Held by Pythagoreans and by Copernicus
,
of the Earth's Motion and Sun's Stability and of the New Pythagorean World System
. Although this was written in the form of a letter to the head of the Carmelite order, the book was a public document. Moreover, although Foscarini's arguments overlapped with Galileo's, they had a distinct flavor and original emphasis: that the earth's motion was probably true and compatible with Scripture.

The publication of Foscarini's
Letter
did not go unnoticed. The Inquisition ordered an evaluation of the book, and a consultant wrote a very critical opinion. But before any formal proceedings started, Foscarini learned about the censure and informally contacted Cardinal Robert Bellarmine, the most authoritative theologian of that time and a member of the Congregation of the Inquisition as well as of the Index. Foscarini sent Bellarmine a copy of his book together with a long letter defending it from the type of criticism contained in the Inquisition consultant's report. Bellarmine replied courteously in a famous letter directed to Galileo as well as to Foscarini and discussing epistemological as well as scriptural issues. Galileo soon received a copy of Bellarmine's letter to Foscarini and immediately started writing a reply now known as “Considerations on the Copernican Opinion,” in three parts. This reply was, however, never published, delivered, or even completely finished because other, more formal Inquisition proceedings soon became the center of attention.

In February 1615, a Dominican friar named Niccolò Lorini, from Florence, filed a written complaint against Galileo with the Inquisition in Rome, enclosing his “Letter to Castelli” as incriminating evidence. Then in March, another Dominican, Tommaso Caccini, made a personal deposition against Galileo with the Roman Inquisition. An investigation was launched that lasted about a year. As part of this inquiry, a committee of Inquisition consultants reported that the earth's motion is absurd and false as a matter of natural philosophy and heretical, or at least erroneous, as a matter of religion and theology. This judgment reflects the weight of the traditional objections to the earth's motion; the failure to know or appreciate the new arguments in its favor; and the unwillingness to question the biblical fundamentalism according to which the Bible is an authority on physical questions, as well as on questions of faith and morals. The Inquisition also interrogated other witnesses. Galileo himself was not summoned or interrogated partly because the key witnesses exonerated him and partly because Galileo's letters had not been published, whereas his published writings did not contain either a categorical assertion of Copernicanism or a denial of the scientific authority of the Bible.

However, in December 1615 Galileo went to Rome of his own accord to defend his views. He was able to talk to many influential Church officials and was received in a friendly and courteous manner; and he may be given some credit for having prevented the worst, insofar as the Inquisition did not issue a formal condemnation of Copernicanism as a heresy, in accordance with the consultants' report. Instead two milder consequences followed. In February 1616, Galileo himself was given a private warning by Cardinal Bellarmine (in the name of the Inquisition) to the effect that he was forbidden to hold or defend the truth of the earth's motion; Galileo agreed to comply. And in March, the Congregation of the Index published a decree which, without mentioning Galileo at all, declared that the earth's motion was physically false and contradicted the Bible; that Foscarini's
Letter on the Earth's Motion
was to be condemned and permanently banned; and that Copernicus' book
On the Revolutions of the Heavenly Spheres
(1543) was temporarily banned until appropriately corrected. These corrections were not specified until 1620 when the Congregation of the Index issued another decree explaining how a dozen passages in Copernicus' book were to be deleted or reworded in order to eliminate from it any suggestions that the earth's motion was or could be physically true and compatible with the Bible; the revisions were also meant to make it clear that the book was treating the earth's motion merely as a hypothesis, which in that context meant a mere instrument of astronomical calculation and prediction.

The events of 1616 marked a turning point in Galileo's career. He was no longer free to research the earth's motion, since he was not supposed to hold or defend it but was to limit himself to discussing it hypothetically or instrumentalistically. He might have taken this opportunity to abandon the Copernican research program and go back to the earlier studies of falling bodies, which he had set aside in 1609. But apparently he felt the Copernican possibility was too important to be set aside completely. At any rate, the import of the new restrictions was not clear; perhaps he could do some useful work while operating under them. This turned out to be the case on the occasion of the controversy over comets that led to
The Assayer
.
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[§0.8] In 1618 three comets appeared in succession, the third being especially bright and long-lasting. As usual, the appearance of such phenomena produced considerable discussion. Sometime between mid-December 1618 and mid-January 1619, they were the subject of a lecture at the Jesuit Roman College. The lecture was published the following month with the title
Astronomical Disputation on the Three Comets of the Year 1618
. The author was anonymous, but the pamphlet indicated that he was a professor at the Roman College. He was soon identified as Orazio Grassi (1590–1654).

Due to ill health, Galileo was unable to make any observations of those comets. However, many people were soliciting his opinion. Thus, he decided to collaborate with a friend and disciple named Mario Guiducci (1585–1646) in writing a short work on the subject entitled
Discourse on the Comets
. This book was published in Florence in June 1619, but only under Guiducci's name. Since the
Discourse
was critical of the views advanced in the
Astronomical Disputation
, Grassi immediately wrote a lengthy reply, publishing it under the pseudonym of Lotario Sarsi, who was allegedly one of his students. Grassi's reply appeared in Perugia in October of the same year with the title
Astronomical and Philosophical Balance
, to convey the idea that Galileo's and Guiducci's ideas were being carefully weighed.

By then the discussion had become so heated that Galileo was being urged to publish under his own name a reply to Grassi's
Balance
. This pressure was coming especially from the other members of the Lincean Academy, who had come to dislike not only Grassi's view of comets but also the Jesuits' claims of leadership in mathematics, astronomy, and natural philosophy. Galileo worked on his reply for about two years, and then it took another two years for the manuscript to be revised, to be issued the imprimatur, and to be printed. Entitled
The Assayer
, the book was published in Rome in October 1623, under the sponsorship of the Lincean Academy. Moreover, it so happened that Cardinal Maffeo Barberini, who was an admirer of Galileo and a friend of the Lincean Academy, was elected Pope Urban VIII in the summer of 1623; so the new book was dedicated to the new pope, who appreciated the gesture very much.