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The Galileo Affair, Part 1: Introduction

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By Paul Newall (2005)

The trial and resulting abjuration of Galileo before the Holy Congregation of the Catholic Church at the convent of Minerva on the 22nd of June, 1633, has been studied by scholars and laymen alike for several hundred years. Not surprisingly, the sheer number of personalities involved, together with the numerous currents playing a part in political, religious, philosophical and scientific affairs over the course of Galileo's life have given rise to a great many interpretations of what happened and—perhaps more importantly—why.


What happened to Galileo has, in particular, been examined at length as an historical event that can shed light on a few specific questions; namely:

  • What is the relationship between science and religion?
  • How did modern science develop, and why?
  • What is the relationship between science and society?

Although it has also been viewed as a human tragedy (Brecht, 1966), the first of these has tended to be paramount. Some mythical perspectives seemed well-supported by a cursory glance and the trial has since come to be known as a paradigmatic example of the inherent conflict between science and religion.

The Myths

According to one of these readings, Galileo knew the Earth to go round the Sun, as Copernicus had written, rather than the converse as implied in several Biblical passages. The Church would not allow science to disprove the revealed truth of Scripture, however, and hence threw Galileo to the Inquisition where he was forced under threat of torture to disclaim this opinion and never speak of it again. He was then imprisoned under house arrest for the remainder of his life, a clear example of the conflict between scientific investigation of the world around us and the presumed infallible authority of the Bible.

Another, less well known myth states instead that the Church had been correct to deal with Galileo as it did. Having seen no convincing scientific evidence or reasons to abandon the Ptolemaic Earth-centred system, the Church ignored Galileo's skilful rhetoric and held to the eminently reasonable approach of not abandoning an idea that was supported both by common sense and Scripture for an alternative that was unproven and had more than enough problems of its own. Galileo was trying to force society and religion to adjust to science that was either disputed or inconclusive, and he was rightly rebuffed and his objections dismissed.

In this essay we shall look at Galileo's early life before considering in more detail the events that became known as The Galileo Affair. Following Finocchiaro (1989, 10), we shall distinguish between non-intellectual (political, personal and social) and intellectual (theological, philosophical and scientific) factors before looking at the trial and its consequences. We shall also consider the recent position taken by the Church under John Paul II and the new fictions introduced thereby. Under the weight of all these diverse aspects, these myths will hopefully give way to a deeper appreciation of the whole affair. Initially, however, we shall reflect on the astronomical problem that provides the overall context for what is to come.

Unless otherwise noted, all references are to Antonio Favaro's Edizione Nazionale delle Opere di Galileo Galilei, with the volume and page numbers given by Roman and Arabic numerals respectively. This is the standard collection of works and correspondence in Galileo studies.

Astronomical Systems

In order to understand the debate that had been ongoing in European religious, philosophical and scientific circles since the publication of Copernicus' De revolutionibus orbium celestium in 1543, we first need to understand the different terms and world systems involved. From the time of Aristotle (384-321 B.C.E.) it had been thought that the Earth stood still (which we call geostaticism) at the centre of the universe (and hence geocentrism). Everything in the universe was part of one of two distinct worlds: that made up by the sublunar and that of the heavenly bodies. The former were made up of earth, fire, air and water, each of which had its natural motion: earth and water, being heavy, moved from high to low; while fire and air, being light, moved from low to high. Once something reached its natural place it no longer moved—much like a pendulum slowing down until it reaches an equilibrium. This meant that the sublunar world must consist in a core of earth with the other elements arranged in "shells" around it—water, air and fire. Since the Earth was mostly earth, it sat at the centre of the universe and did not move.
The simplified Ptolemaic system, sometimes called Aristotelian
The heavenly bodies, being separate, could not be composed of the four elements; so Aristotle invoked a fifth—the ether. They could not move toward the centre, since that was occupied by the Earth, so their natural motion had to be circular, becoming neither closer nor farther away as they moved. A circular motion, however, could continue indefinitely in one direction and hence there would be no opposition—and so no change. The heavenly bodies, then, were immutable. All this was set in motion by God, the final mover, the result being much like an onion: a central Earth surrounded by concentric spheres, just as the onion is made up of a centre around which the layers are arranged one on top of each other.

Although much of this model seemed confirmed by observation and common sense, it struggled to explain phenomena that became increasingly familiar to early astronomers. Why did the brightness of the planets vary? What of retrograde motion, where a planet appeared to move eastward for most of the year but then to go back on itself, westward, before heading east again—tracking a loop across the heavens, as it were? These difficulties made it hard to claim that the Aristotelian representation could be an accurate picture of the universe.

This situation changed significantly with the work of Ptolemy, who is estimated to have lived from circa 100-178 C.E. His Almagest (a name given to it by the Arabs, from al—the Arabic "the"—and megiste—the Greek "greatest"—to set it apart from another textbook called The Little Astronomer) was based on observations from 127 to 151 and gave a mathematical account of the movements in the heavens. In particular, he affirms in chapters five and seven of Book One that the Earth is central and does not move. His explanations were based on three principles:

  • The eccentric, according to which the Earth is not at the centre of planetary orbits but slight off.
  • The epicycles, according to which a planet revolved around a circle (an epicycle) which, in turn, was centred on a deferent. The deferent could itself be on another deferent, and so on, allowing Ptolemy to account for retrograde motion.
  • The equant, according to which the angular velocity (or speed of revolution) of a deferent was not constant with respect to its centre but instead off-set slightly at an equant point, so that the angular velocity would be greater the farther away from the equant, and vice versa. This would help explain the speeding up of the planets at various times of the year.

Diagram reproduced with permission from Nick Strobel's Astronomy Notes site.

With these mathematical devices, Ptolemy was able to describe the motions of the planets in mathematical terms so successfully that his account would still be in use some 1400 years later. Although he himself tried to interpret his work realistically in his Hypothesis on the Planets, a lasting consequence of his treatment was the separation of astronomy and natural philosophy (or what we would now call science): the task of the astronomer was not to give a true explanation of the structure of the universe and how it functions, but merely a tool or instrument of prediction to help in calculating positions when required.

The first geokinetic ("moving Earth") system was implicit in that of Philolaus in approximately 475 B.C.E., which, though now lost, was referred to by Archimedes and others. Nevertheless, a true heliocentric ("sun centred") approach was devised by Aristarchus of Samos in the fourth century B.C.E. This was not heliostatic (i.e. the Sun standing still) since the Sun rotated on its own axis. His account was rejected by Aristotle and others because of the theory of natural place (explained above), the lack of any common experience that suggested its truth, and—most importantly—because the phenomenon of stellar parallax was not noted.

Diagram reproduced with permission from Nick Strobel's Astronomy Notes site.

This was an argument that noted that, on the assumption of a moving Earth, the line of sight from an observer to a star would not remain parallel over the course of a year but would vary. Aristarchus thought that this was because the universe is so vast in extent that the change would be negligible, but, with his system not coming close to the mathematical sophistication of Ptolemy's, this idea was rejected along with the motion and rotation of the Earth.

Copernicus, the heliocentrist.

With some other minor developments that are beyond the scope of this essay, this was how matters remained until the publication, on his deathbed (literally) of Nicholas Copernicus' (1473-1543) De revolutionibus orbium celestium. In that work he gave a mathematical account of a universe centred on the Sun, in which all the planets (and the Sun itself) rotated on their axes and around the Sun.

Although Copernicus interpreted his model not as an instrument but as a description of reality, a preface was added to his work by Andreas Osiander which asserted to the contrary in order to avoid the censure of the Church. The reception given to Copernicanism varied between countries and over time, but one of the most important responses was given by the Danish astronomer Tycho Brahe who developed an alternative system, according to which the planets orbited the Sun and the Sun, in turn, orbited the Earth.

This retained geocentrism and geostaticism, winning the support of astronomers in the instrumental tradition. Others, however, complained that it was merely a mathematical concession that did not address the physical difficulties with the Ptolemaic system that were brought up by the appearance of many comets between 1577 and 1596. Aware of these issues, Brah could not bring himself to accept Copernicanism. A more detailed account of the background may be found in a study of the history of astronomy (cf. Kuhn, 1971 and Fantoli, 1996 for recent examples), but this was the situation when Galileo arrived on the scene.

Galileo the Man

Galileo Galilei was born in the environs of Pisa on the 15th of February, 1564, the son of Vincenzio Galilei, a musician and teacher of music who emphasised the use of experiment and was scornful of any deference to authority. His mother was Giulia Ammanati, known from her letters to have been a difficult woman. He was schooled initially by the monks at Vallombroso until his removal by his father due to problems with his eyesight and was later enrolled at the University of Pisa in 1581 to study medicine. In 1583 he began to take private lessons in mathematics from Ostilio Ricci, a tutor associated with the Tuscan court. His father's disagreement with this change of direction was assuaged somewhat by Ricci's intervention. Galileo left the university without graduating, intending to devote his efforts to mathematics, but unable to win a scholarship from the Grand Duke.


Some work on the centres of gravity of solids won Galileo the admiration of Christopher Clavius, a famous Jesuit mathematician whom he visited in Rome in 1587, together with the patronage of the Marquis Guidobaldo del Monte. Both were able to use their influence to help Galileo gain the chair of mathematics at his old university in 1589, having failed the year previously to win the same position at the University of Bologna. It was in Pisa that he was reputed to have carried out his famous experiments, dropping weights from the leaning tower.

More accurately, these were demonstrations, not experiments, because Galileo already knew what to expect from his childhood experience of watching falling hailstones of different sizes striking the ground at the same time and the prior suggestion (1553 and 1586 respectively) and testing by others (Giambattista in 1553 and Stevin in 1586; cf. Drake, 1999, 1: 8) of this result—contrary to Aristotelian teaching. (According to Aristotle's ideas on impetus and place, a heavy stone should fall proportionately quicker, attempting to regain its natural place.) Although some historians of science have doubted whether this celebrated incident ever occurred (Koyre, 1978 and Dijksterhuis, 1969: 336, for example), the matter was settled by Thomas B. Settle's repetition, observation and explanation of the curious fact that the heavier ball descends slightly behind the lighter—a puzzling circumstance noted by Galileo and found by Settle to be due to differential muscular fatigue, leading to the early release of the lighter ball even though the holder believes the release to be simultaneous (Cohen, 1992: 195; see also Drake, 1999, 1: 309 for how Settle's work oust the Koyrean programme within Galileo studies).

Soon after his arrival at Pisa, Galileo had written a paper on mechanics that would perhaps have been sufficient to displace Aristotelianism and certainly win him a reputation in the wider world (Drake, op cit, 28). He preferred instead to continue working and ultimately never published it. We should bear this in mind when considering the later suggestion that he lacked prudence or defended ideas he knew to be untenable.

Disappointed with his prospects of advancement, Galileo resigned from his position in 1592 and, again with the aid of Guidobaldo, took up the chair of mathematics at the University of Padua, then part of the Venetian Republic. The intellectual climate there was more to his liking, the government in Venice being easily the most tolerant of the Italian states while the great Vesalius had taught at the university. There Galileo met and befriended Giovanfrancesco Sagredo, who would later take the third role in Galileo's Dialogue. In his time at Padua he invented several devices that found medical applications after their adaptation by Sanctorio Santorius, the professor of medicine. It was here also that Galileo first met Roberto Cardinal Saint Bellarmine, who would play such an important role in later events. Galileo lodged for a time with G.V. Pinelli and it is reckoned that a later meeting there, involving Bellarmine and Cesare Baronius—the latter a cardinal, too—was the source of a maxim attributed to Baronius by Galileo some years hence, according to which "the Bible tells us how to go to heaven, not how the heavens go." (Drake, op cit.)

In 1597 Galileo was given a copy of Johannes Kepler's Precursor of the Cosmographic Dissertations or the Cosmographic Mystery and struck up a correspondence with the author. They discussed Copernicanism and Galileo mentioned his concern at the fate of Copernicus' ideas (X, 68). Also in 1597, Galileo invented a "geometric and military compass", or what we would today call a sector. In 1599 he began to manufacture these commercially by taking on a craftsman, such was their utility. Over the next few years he was able to prove several theorems concerning motion on inclined planes and discovered the law of falling bodies.

Although he never married, Galileo formed a relationship with Marina Gamba and had two daughters, in 1600 and 1602, followed by a son in 1606. He was utterly devoted to his eldest daughter, Virginia, who wrote many letters to him and maintained his spirits during his later difficulties with unwavering faith in him. When she died in 1634, he was inconsolable and probably never recovered from his loss.

In 1604 an event occurred that perhaps marked the beginning of his troubles with the philosophers. A supernova was observed in the night sky and Galileo was called upon to give lectures on it. These were so popular that no spares seats could be found and Galileo pointed to what had occurred in the heavens as evidence that Aristotle had been incorrect in supposing that the sphere beyond the planets was composed of a perfect and immutable quintessence that could not be altered.

The Paduan professor of philosophy, Cesare Cremonini, replied to Galileo in a small booklet, to which the latter responded in turn—probably in collaboration with his friend Antonio Querengo—by composing a dialogue in rustic Paduan dialect between two peasants (Drake, op cit). In this work the peasants made a mockery of the Aristotelians and, although published under a pseudonym, it was widely known to have been Galileo's creation. A student in Padua called Baldessar Capra criticised this work in a pamphlet of his own, in addition to plagiarising the handbook that Galileo had written for the use of his military compass. In 1607, Galileo published his Defence against the calumnies and impostures of Baldessar Capra, in which he answered these objections alongside an account of bringing the theft of his ideas to the attention of the authorities. During the resulting trial he had demonstrated that Capra did not sufficiently understand either the instrument or the principles behind it. Capra's work was prohibited and he was expelled, while Galileo was never again so open with his ideas.

Hard at work on theorems concerning materials and motion, Galileo discovered that projectiles follow parabolic paths but did not publish his thoughts until late in his life. The event that compelled him to put these inquiries aside was to have a profound influence on his work: the invention of the telescope. In 1608 the Dutch optician Hans Lippershey had built the first example and tried to patent his invention. Hearing about it from his friend Paolo Sarpi, Galileo realised that he could manufacture his own from convex and concave lenses placed at the objective and eyepiece end of a tube respectively. Able to achieve a nine-fold magnification, he presented his telescope to the Venetian government and was offered an appointment for life together with an increased salary. On further examination, however, it transpired that no further raises would be permitted. Galileo was hoping for a better deal, so he continued to develop his telescope and looked to the Tuscan Court instead.

Galileo's Telescope.

By 1610, Galileo's telescope could magnify thirty times and he did something that very few had thought to do (there is evidence that Thomas Harriot had already been observing the moon—cf. Cohen, 1992: 185): armed with this new tool, he turned his augmented attention upwards to gaze deeper into the heavens than anyone before him. Close attention to and sketches of what he saw over a period of many nights revealed to him that the moon was not smooth at all but mountainous. He also discovered vast numbers of stars and the four satellites of Jupiter. Publishing the results of these investigations in his Sidereus nuncios (or Starry Messenger), he dedicated the work to Cosimo II de' Medici, his former student and now Grand Duke of Tuscany. Christening the four moons the "Medicean Stars" in a shrewd move, Galileo applied for and was granted the position of Chief Mathematician and Philosopher to the Grand Duke, as well as Chief Mathematician of the University of Pisa with no requirement to either teach or live there. He was also granted a salary of 1000 scudi, a large amount of money at that time and which was soon to rouse the envy of other ducal courtiers (although it was nothing like the pay of a professor of philosophy—a circumstance that would bother him throughout his later life).

In Florence, Galileo observed the phases of Venus and the strange form of Saturn. He received Kepler's Conversation with the Starry Messenger, offering the latter's support for his discoveries. Nevertheless, there were plenty of hostile reactions: a gathering led by Giovanni Magini, professor of mathematics at Bologna, had been unable to see the Medicean Stars through the telescope, even with Galileo present to help them; Martin Horky, a student of Magini's, published A Very Short Excursion Against The Starry Messenger; and Ludovico delle Colombe wrote Against the Earth's Motion, in which he marshalled religious criticisms of Galileo's idea. Cesare Cremonini and Giulio Libri, professors of philosophy at the universities of Padua and Pisa respectively, refused even to look through the telescope. Christopher Clavius in Rome stated that the satellites were a trick of the lenses, not real objects in the heavens.

In spite of these, Galileo gave three public lectures in Padua and the Jesuits in Rome, including Clavius, verified his observations as soon as they obtained a suitably powerful telescope. Finally, on the 20th of March, 1611, Galileo arrived in Rome where he was feted as a hero, welcomed by Cardinals and provided with opportunities to give demonstrations in the gardens of the rich and powerful. He was granted an audience with Pope Paul V, inducted into Marquis (later Prince) Federico Cesi's Accademia dei Lincei (the Academy of the Lynx-Eyed, the first scientific academy) on the 25th of April, and received with much ceremony by the Jesuits at the Roman College on the 13th of May where an address entitled The Sidereal Message was read in his honour in the presence of the entire College and many Cardinals.

At this point, then, Galileo was at the apex of his fame. There were plenty waiting in the wings to attack him, however, and those who already had—for a variety of reasons. It is to these that we shall now turn.


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