GALILEI, GALILEO. – Born on 15 Feb 1564 in Pisa to Vincenzo, a Florentine, and Giulia degli Ammannati from Pescia; in his childhood he was with the Vallombrosan monks; he then enrolled at the University of Pisa in the Faculty of Arts and, around the age of twenty, devoted himself with particular zeal to mathematics. The environment in Pisa was thoroughly Aristotelian, but this did not deter the young scholar from proceeding independently, basing his work on the study of Archimedes and on experiment. In 1587 he went to Rome, where he came into contact with the Prince of Mathematicians (Clavius), professor of mathematics at the Collegio Romano (d. 1612), with whom he maintained excellent relations thereafter. In 1588 he unsuccessfully sought the chair of mathematics at the University of Bologna; in July 1589, however, he obtained the professorship at Pisa; and, failing to secure its renewal, he moved to the University of Padua, where he was appointed by decree of the Venetian Senate on 26 Sept 1592. The years in Padua were truly decisive for G.’s scientific career and provided an incentive to intense activity. In addition to delivering public lectures as required, he gave private lessons and ran a boarding house for students; he set up a workshop for precision instruments: compasses, quadrants, squares, etc., and later lenses and telescopes; he made friends among the Venetian nobility and had illustrious disciples, including Gian Francesco Sagredo, the monk Benedetto Castelli, and the canon Paolo Apronio. During these years, from a relationship with Marina Gamba he had Virginia (later Sister Maria Celeste), Livia (later Sister Angelica), and Vincenzo, whom he later took with him to Florence. With the precise aim of popularizing science, he began his career as a writer in the vernacular, in which he always succeeded with remarkable clarity, precision, and brevity, avoiding unnecessary citations and any rhetorical flourish, thereby resolutely opposing the bad habits of his time.
From this early period date a Treatise on the Sphere, a Treatise on Fortifications, several manuscripts of a practical nature On Mechanics, and a pamphlet On the Compound of Proportion (1606), which illustrated an instrument he had constructed to speed up calculations. By 1597 he was already a convinced Copernican; he corresponded with Kepler but could not openly profess his views; above all, he devoted himself to refining his scientific method, the consistent application of which allows G. to be called the father of modern science. From the outset, his aim was to follow the method taught by mathematicians, namely, to derive what one says from what has been said, never assuming as true what one seeks to explain; whereas according to the prevailing methods and those learned by rote, people never know things from their causes but merely accept them on faith, that is, because Aristotle said so. “If what Aristotle said is true, few bother to investigate; it is enough for them to be considered learned because they have more Aristotelian texts at hand” (Opere, ed. nazionale, I, p. 285). The rational interpretation of phenomena, together with the investigation of their mutual dependencies through, as far as possible, mathematical deductions, finds in G. its first conscious and complete expression: “I truly esteem the book of philosophy (taken in the broadest sense of natural philosophy) to be one that is perpetually open before our eyes; but because it is written in characters different from those of our alphabet, it cannot be read by everyone; and the characters of this book are triangles, squares, circles, spheres, pyramids, and other mathematical figures most apt for such reading” (ibid., XVIII, p. 293). Here, while G. on the one hand reveals his preference for geometry among the mathematical sciences, on the other he insists on direct experience, to which the speculations of the ancients may indeed contribute, provided they do not conflict with what direct experience teaches. In this sense, G. would be an incomparable master of an experimental method to famous disciples, and this new school would completely renew the study of nature.
G.’s investigations from the outset ranged over diverse fields. As early as 1602 he was working on magnets, which he manufactured, increasing their power of attraction; simultaneously, he studied heat phenomena, on which his disciple Sagredo also worked; hydraulic problems were not foreign to him either. But it was problems relating to motion and gravity that particularly occupied his activity throughout his scientific life. He had already addressed these in Pisa, where he also observed the isochronism of small oscillations of the pendulum and began to compile his notebooks on new weights and engaged in controversy with the Aristotelians over their erroneous conclusions; in Padua he was already occupied with the remarkable problem of impact and the fall of projectiles, topics that would later become the subject of broader developments. Astronomical problems were also connected with those of motion, but G. did not make them the object of study until a later period; of the comet of October 1604, which he did observe, he left no scientific treatment.
The second period began in 1609, which brought G. into a wider field of activity and fame. The vague news that in the Netherlands a certain spectacle-maker had constructed an instrument with lenses that made distant objects appear near induced G. to build one in his workshop (Aug. 1609) and to show it immediately in Venice; he then made many such instruments and for a long time none surpassed him in quality. It is known that he later adapted this telescope to observe minute objects, but this did not greatly interest the inventor; instead, he turned his instrument toward the heavens. This occurred in Jan. 1610, and he immediately observed the lunar spots, the immense multitude of fixed stars, especially in the Milky Way, and their difference from the planets, and the existence of Jupiter’s satellites. He announced these discoveries to the world in the Sidereus Nuncius, printed in Venice in March and written in Latin to make it accessible to all Europe. The Nuncius overturned all the prevailing cosmological conceptions and completely disrupted judicial astrology, which was still in vogue; from the outset, therefore, it met with open incredulity in the scientific world: doubt was cast on the reliability of the telescope and the accuracy and interpretation of the observations. Certainly few could avail themselves of a good telescope to repeat the observations, while others, out of sheer obstinacy, refused to use one, as did Cesare Cremonini, G.’s colleague at Padua. In Germany, however, Kepler was an advocate of G., especially when he could use a good telescope, as were Fr. Clavius and Fr. Tommaso Campanella.
The reputation G. had now earned among true scholars induced Grand Duke Cosimo II to bring him back to Tuscany, and on 10 June 1610 he appointed him first mathematician of the University of Pisa and philosopher and mathematician to the Grand Duke, with no teaching obligations. G. accepted, and on 12 Sept he was in Florence, where he also transferred his workshop. Here he continued his observations on the singular configuration of Saturn, begun in Padua (25 July), and in Sept–Oct 1610 he became convinced of the phases of Venus, analogous to those of the moon, a sign that this planet revolved around the sun from which it received light. The Ptolemaic system was thus completely refuted, but the Peripatetics showed no sign of noticing.
In February 1611 he made a journey to Rome, where he also had occasion to discuss the sunspots he had first observed; he was very well received by Clavius and the Jesuits of the Roman College; Federico Cesi, Marquis of Monticelli, enrolled him in his Accademia dei Lincei, and Galileo took great pride in this; he also received honorable welcomes in the Roman ecclesiastical world, which wished to acquaint itself with his discoveries. In May 1612 he published in Florence, at the invitation of the Grand Duke, his conclusions on floating bodies, following the doctrines of Archimedes and provoking a lively controversy from the irreconcilable Peripatetics. They received another blow from him with the three letters he wrote in the second half of that year to Marcus Welser of Augsburg, communicating his further observations on sunspots in refutation of the letters that Father Scheiner, a Jesuit, had sent on the same subject. These were printed in 1613 under the care of the Lincei in Rome.
In the following years the controversy flared up regarding the acceptability of the heliocentric doctrine in relation to the Faith. Galileo spread this theory in oral discussions and in epistolary correspondence; but, with few exceptions, he found himself opposed by “the universal opinion, as it were, imbibed from the beginning of the world.” To some, even learned men, it seemed that the Tychonic system was sufficient to reconcile the new discoveries with religious tradition. Moreover, it was a widespread custom to introduce into discussions—even purely philosophical ones—the authority of Scripture and the Fathers, and this was not omitted in the heliocentric question, in order to condemn it as contrary to the Faith and heretical. In December 1613 Father Castelli had held a discussion on the subject “in Pisa before the Tuscan court and had reported it to Galileo. He took up the matter again in a long letter to Castelli on 21 December, which was promptly circulated, showing how poorly those who dragged Scripture into such matters proceeded and how weak were the proofs they claimed to derive from II. Instead, with a properly theological intention, Father Paolo Antonio Foscarini, a Carmelite (d. June 1616), entered the field early in 1615 at Naples with a letter in which, after praising Galileo, he showed very well how the scriptural and patristic passages alleged against the heliocentric doctrine were quite incongruously cited and admitted of different interpretations. Galileo became acquainted with this letter, which was soon printed; he took heart in the same year to address a truly admirable letter—clear and precise even theologically—to Maria Cristina, mother of the Grand Duke, in which he developed the arguments already touched on in the letter to Castelli and others; and, showing the relationship between science and faith, he refuted the opposing arguments in turn. It was not he who had brought the discussion into the scriptural field, but necessity had driven him there in order to safeguard his position as both scientist and believer. This letter was not printed at the time, but copies were circulated among the learned circles of Tuscany.
On 7 February 1615 Father Niccolò Lorini, a Dominican, sent from Florence to Cardinal Paolo Sfondrati, Prefect of the Congregation of the Index, a copy of Galileo’s letter to Father Castelli, calling it “many propositions, some of them rash and suspect.” Since the letter was not printed, the cardinal forwarded it to Cardinal Mellini, Secretary of the Holy Office, where it was promptly examined. On 20 March Father Tommaso Caccini, also a Dominican, formally denounced Galileo to the Holy Office, and a judicial inquiry was therefore initiated in Florence. Realizing that Florentine enmities would not fail to have repercussions in Rome, Galileo decided to go there without further delay. He hoped to win over the more learned elements of the Eternal City, disregarding the warnings of friends that “the Peripatetics were most powerful there.” Many illustrious figures, even in the Curia, who esteemed his studies and discoveries did not wish to follow him along this path. In the fervor of his convictions, Galileo failed to realize how difficult it would be to dismantle a philosophical construction taught as unassailable in all ecclesiastical and secular schools, and how hard it must have seemed to those masters to renounce doctrines held for many years with full conviction. Leaving Florence with the Grand Duke’s permission, Galileo arrived in Rome on 11 December 1615, as the guest of the Grand Duke’s orator on the Pincio, and immediately set to work vigorously, disputing his theories with the most prominent figures, even with Father Caccini, putting his arguments into writing and thereby provoking the opposition of the adherents of the old systems, who made it a matter of religious orthodoxy. All this led to the necessary conclusion that the relationship between Copernican theory and Christian tradition should be clarified, and the discussion thus officially transferred from the personal to the strictly doctrinal sphere. It was easy, therefore, for Galileo’s opponents to persuade the Holy Office of the need for a decision that would remove all uncertainty. The Holy Office referred the matter to a commission of eleven theologians, who on 24 February 1616 answered the two questions put to them as follows: 1) “that the sun is at the center of the world and motionless in local motion is a proposition that is absurd and false in philosophy and formally heretical, because it is expressly contrary to Holy Scripture”; 2) “that the earth is not the center of the world nor motionless, but moves even with a diurnal motion: this is likewise an absurd and false proposition in philosophy, and, considered theologically, is at least erroneous in faith.” This response of the theologians was ratified the next day by the cardinals of the Inquisition, in the Pope’s presence; but it was not given official publication as an act of the Sacred Congregation and remained as an internal rule, as the conclusion of learned and qualified men on the subject.
As for Galileo, who had publicly compromised himself with his discussions, it was desired to proceed against him in a lenient manner, and Cardinal Bellarmine was entrusted with officially admonishing him to desist from propagating such theories, with the threat that, in case of disobedience, he would be imprisoned. On 26 February the cardinal carried out this duty in the presence of the Commissioner of the Holy Office and some witnesses. Galileo promised to obey, pledging “in no way to hold, teach, or defend in speech or in writing” heliocentric doctrines. Meanwhile, on 5 March, the Sacred Congregation of the Index prohibited Foscarini’s book along with all others, not listed, that upheld the same doctrines, and decided that in new editions of Copernicus’s work certain phrases should be corrected so that it would appear that he had proposed the heliocentric system merely as a astronomical hypothesis. Since it was spreading by word of mouth that Galileo
He had been compelled to a formal abjuration, and he took care to obtain from Cardinal Bellarmine, on 26 May, a certificate attesting that the communication regarding the Copernican theory had been made to him. Thus ended what was inappropriately called G.’s first trial. In early June he returned to Florence, more determined than ever to promote the triumph of his doctrines in the best and most prudent manner, by demonstrating at that time the inconsistency of opposing doctrines.
The year 1618 was the year of the comets: three appeared, the last of which (November 1618–January 1619) aroused particular interest among astronomers and the public. The main discussion concerned their nature: whether they were true planets or mere meteors. Galileo’s judgment was awaited, but he was ill and could not make direct observations. Instead, Father Orazio Grassi, an astronomer of the Roman College, published a public disputation: *De tribus cometis*, and Galileo seized upon this publication, arranging for his friend Filippo Giordano to deliver a discourse at the Florentine Academy in response. Rather than establishing a doctrine, the lecture was intended directly to demonstrate the inconsistency of Grassi’s theories and those of other astronomers, including Tycho Brahe, complaining that instead of direct observations, people reasoned only on the basis of preconceived theories. Father Grassi replied under the guise of a supposed pupil defending his master’s doctrine, and under the name of Lotario Sarsi Sigensano published in Perugia the *Libra astronomica ac philosophica* (1619) in refutation of Giordano. Galileo’s friends agreed that a response was necessary, and in October 1623 he published *The Assayer*, in which, in 52 chapters, he examined all of Sarsi’s assertions. It is a polemical work, not a properly systematic treatise, in which the author carefully avoids presenting himself as a defender of the Copernican theory, though he occasionally insinuates its superiority, demolishes Sarsi’s assertions and objections to Giordano’s discourse, and observes that in scientific research one must rely more on direct observation of phenomena and on mathematics than on the opinions of authors; for this reason he avoids citing Sacred Scripture, as unfortunately was often done. The book, addressed to the young Roman patrician Virginio Cesarini and dedicated to the new Pope Urban VIII, enjoyed wide circulation and provoked a counter-reply from Father Sarsi. Confident in the benevolence that Urban VIII had shown him years earlier, in April 1624 Galileo undertook a new journey to Rome, where he was promised ecclesiastical benefits, but as regards acceptance of his ideas he encountered only disappointment. Thus, almost as an excuse while refuting his adversaries, he wrote that he did not intend thereby to uphold Copernican doctrines, but to make known to heretics that, even if he could not accept them, he was not ignorant of the arguments on which they were based.
Meanwhile, a new argument presented itself to Galileo in favor of heliocentrism: the ebb and flow of the sea. He refused to entertain the influence of the stars, almost as a reaction to one of the cornerstones of contemporary astrology, and therefore believed that the cause of the tides had nothing to do with the influence of the sun and moon; in his view, they were due to the rotation of the earth. He wished to frame this new hypothesis within a broader treatise that would examine the two greatest cosmological systems: Ptolemaic and Copernican. He began work in the autumn of 1624, but only in October 1629 did he apply himself to it with the intention of bringing the work to completion. It is conceived as a dialogue divided into four days with three interlocutors: Filippo Salviati, who upholds the Copernican side while repeatedly professing to reason as a scientific hypothesis that faith does not accept; Gian Francesco Sagredo, who plays the part of the learned but secular listener, clarifying the arguments; and Simplicio, the traditionalist—not ignorant or foolish, always attached to the doctors and books, without contact with nature or experiment—who, not without caricature, defends current ideas. They debate the nature of the heavens, the diurnal motion of the earth and its motion around the sun, the ebb and flow of the sea, and the fall of heavy bodies.
Florence, 20 January 1633. He arrived in Rome on 12 February and presented himself before the tribunal. He was granted residence in the palace of the Tuscan ambassador, Nicolini, at the Pincio, with the obligation to live in seclusion. Only on 12 April was he required to enter the palace of the Holy Office, where he was assigned the three rooms available, without locks, with freedom to go into the courtyard, to keep a servant, and to receive food from the embassy. The interrogation began at once. Galileo had hoped to be allowed to defend his theories, but this was not the practice of the tribunal, for which his views had already been condemned since 1616. Indeed, the first question of Father Commissioner Vincenzo Maculano concerned the injunction issued to him at that time by Cardinal Bellarmine. Galileo admitted to being the author of the *Dialogue*, adding that in that book he had neither held nor defended the opinion of the mobility of the earth and the stability of the sun. On this denial Galileo attempted to found his defense, whereas, as the commissioner rightly noted, the contrary “manifestly appears in the book he composed.” To spare him harsher measures, the commissioner obtained permission to treat the matter extrajudicially with him, and on 20 April induced him to admit that he had exceeded in his book in favor of Copernican doctrines. In the second interrogation on 30 April he admitted that “the arguments advanced on behalf of the false (Copernican) side, which he claimed to be refuting, were so presented that by their force they were more compelling than easy to unravel,” and he declared himself ready to write in the opposite sense and to add “one or two days to his dialogue for this purpose.” After this second interrogation, Galileo was again permitted, for reasons of health, to remain “in loco carceris” in the palace of Ambassador Nicolini, while remaining at the disposition of the Holy Office.
In the third summons before the Holy Office on 10 May, regarding the precept imposed in 1616, G. insisted in asserting “that he had not knowingly and willingly transgressed the commands given to him” at that time, and with regard to the *Dialogue* he merely referred to what he had said in the first interrogation. He may have hoped to avoid a formal abjuration, but it was clear that his assertions were not true. After this, on 16 June the Pope communicated his decisions: G. was now to be interrogated without delay regarding what he truly believed (*signi intentione*), even with the threat of torture; and if he persisted, he was to abjure so as not to be handed over to the Cardinal Congregation with the injunction never again to treat Copernican doctrine in any way, under penalty of being treated as a *relapsed*; the *Dialogue* was to be prohibited and the sentence made public, sending it to nuncios and inquisitors in various countries, especially Florence.
The interrogation “on intention” took place before the Commissary on 21 June and again on 6 September, when G. declared that before 1616 he had been indifferent between the two great systems, but that after that he had no longer defended the Copernican system. When the threat of torture was made, he replied that he would obey, again insisting on his denial regarding the Copernican system. The threat was merely a procedural element and, according to the rules, could not in fact have been inflicted on him, being old and ill; indeed, “he was sent back to his place,” and the next day, in the convent of Santa Maria sopra Minerva, before the cardinals and prelates of the Congregation, the sentence was read to him. In it, while acknowledging that G. had not spoken entirely truthfully, it was recognized that in the rigorous examination he had answered in a Catholic manner; in any case, he had rendered himself “vehemently suspect of heresy,” incurring the relevant censures and penalties, from which he was absolved after his abjuration; the *Dialogue* was prohibited, and the author, condemned in 1616 to imprisonment in the Holy Office at the discretion of the Congregation, was ordered to recite the seven penitential psalms once a week for three years. G. made the prescribed form of abjuration, accepting the obligations imposed upon him.
This was the end of G.’s trial, for without re-examining the doctrinal decision of 1616 regarding the religious unacceptability of the Copernican system, he was condemned on the grounds of his continued adherence to it, demonstrated above all by the *Dialogue Concerning the Two Chief World Systems*. He was now a prisoner of the Holy Office, though as his prison he was assigned the Palazzo dell’Orologio on the Pincio; on 30 June he was granted the grace of residing “in Siena with that city’s archbishop Ascanio Piccolomini”; then on 1 December he was permitted to retire to his villa at Il Gioiello near San Matteo in Arcetri, which he had purchased on 27 September 1631, and there he remained as a prisoner until his death. Indeed, every attempt to obtain full pardon for him proved vain: Urban VIII would not hear of II.
G.’s final years were darkened by troublesome illnesses, from which he was deprived of the comfort of his daughter Sister Maria Celeste, who died on 2 April 1634; in December 1637 he became completely blind. He was particularly grieved by the prohibition on the printing of all his works. Yet he never ceased his studies, especially on the subject of “resistance,” as he himself wrote on 12 July 1636, and he composed a volume on it which the Elzevir press in Leiden published in 1638; it was soon sold even in Rome: *Discourses and Mathematical Demonstrations Concerning Two New Sciences Pertaining to Mechanics and Local Motions*. The work is in four dialogues with the same interlocutors as the *Dialogue on the Two Chief World Systems*, of which it is a continuation, maintaining a tone no longer polemical but calm and measured. Drawing on his early writings *De motu locali*, the foundations of dynamics, and opposing Aristotle with the law of inertia, he provided the first rational basis for the Copernican system and a secure foundation for Newton’s principle of universal gravitation. But G. pursued other developments of his doctrines as well, which his pupil Vincenzo Viviani, with the notes he had collected, later set down in two additional days appended to the *Two New Sciences*.
Since the States General of the Netherlands had announced a competition to solve the problem of determining longitude during navigation, G. took up again the hypothesis that this might be achieved by observing the eclipses of Jupiter’s satellites with the aid of a good telescope and a clock. On this subject he had been in lengthy correspondence with Spain after 1616, without success; and even on this occasion (1636–40), owing to technical difficulties, he achieved no more than being given a gold chain (1638), which he refused so as not to arouse new suspicions. Until the end he continued to examine his favorite problems; “his last letters concern the tides and the lunar surface,” until piously he closed his life in the arms of his son Vincenzo, Viviani, and Evangelista Torricelli, who had been his pupil in his final months, on 8 January
1642. He was buried in Florence in Santa Croce
See pl. CXXVII.On the third centenary of G.’s death: *Saggi e conferenze*, in the publications of the Università cattolica, Milan 1942.