by Will Durant
To the dismay of all the philosophers, very many conclusions of Aristotle were by him [Galileo] proved false through experiments and solid demonstrations … as, among others, that the velocity of moving bodies of the same material, of unequal weight, moving through the same medium, did not mutually preserve the proportion of their weight as taught by Aristotle, but all moved at the same speed; demonstrating this with repeated experiments from the height of the Campanile of Pisa in the presence of the other teachers and philosophers, and the whole assembly of students…. He upheld the dignity of this professional chair with so great fame … that many philosophasters, his rivals, stirred with envy, were aroused against him.82
Galileo himself nowhere mentions the Pisa experiment in his extant writings; neither is it mentioned by two of his contemporaries who in 1612 and 1641 reported their own experiments in dropping objects of diverse weight from the top of the Leaning Tower.83 Viviani’s story has been rejected as a legend by some scholars in Germany and America.Iv Uncertain, too, is the tradition concerning the resentment of fellow professors at Pisa. He left that university in the summer of 1592, probably because he had been offered a loftier chair at a better fee. In September we find him installed at the University of Padua, teaching geometry, mechanics, and astronomy, and turning his home into a laboratory to which he invited his students and friends. He avoided marriage, but took a mistress, who gave him three children.
Now he made the researches and experiments that he gathered together only toward the end of his life in his Dialogues Concerning Two New Sciences—i.e., concerning statics and dynamics. He affirmed the indestructibility of matter. He formulated the principles of the lever and the pulley, and showed that the speed of freely falling bodies increases at a uniform rate. He made many experiments with inclined planes; he argued that an object rolling down one plane would rise on a similar plane to a height equal to its fall if it were not for frictional or other resistance; and he concluded to the law of inertia (Newton’s first law of motion)—that a moving body will continue indefinitely in the same line and rate of motion unless interfered with by some external force.84 He proved that a projectile propelled in a horizontal direction would fall to the earth in a parabolic curve compounding the forces of impetus and gravity. He reduced musical tones to wave lengths of air, and showed that the pitch of a note depends upon the number of vibrations made by the struck string in a given time. Notes, he taught, are felt as consonant and harmonious when their vibrations strike the ear with rhythmic regularity.85 Only those properties of matter belong to matter that can be dealt with mathematically—extension, position, motion, density; all other properties—sounds, tastes, odors, colors, and so on—”reside only in consciousness; if the living creature were removed, all these qualities would be wiped away and annihilated.”86 He hoped that in time these “secondary qualities” could be analyzed into primary physical qualities of matter and motion, mathematically measurable.87
These were basic and fruitful contributions. They were hampered by inadequacy of instruments; so, for example, Galileo underestimated the factor of air resistance in the fall of objects and projectiles. But no man since Archimedes had ever done so much for physics.
2. The Astronomer
Toward the end of his stay in Padua he gave more and more of his time to astronomy. In a letter (1596) to Kepler (seven years his junior), thanking him for the Mysterium cosmographicum, he wrote:
I esteem myself happy to have as great an ally as you in my search for truth. … I will read your work … all the more willingly because I have for many years been a partisan of the Copernican view, and because it reveals to me the causes of many natural phenomena that are entirely incomprehensible in the light of the generally accepted hypotheses. To refute the latter I have collected many proofs, but I do not publish them, because I am deterred by the fate of our teacher Copernicus, who, though he had won immortal fame with a few, was ridiculed and condemned by countless people (for very great is the number of the stupid). I would dare to publish my speculations if there were more people like you.88
He professed his Copernican faith in a lecture at Pisa in 1604. In 1609 he made his first telescope, and on August 21 he demonstrated it to Venetian officials. Hear his account:
Many of the nobles and senators, although of a great age, mounted more than once to the top of the highest church in Venice [St. Mark’s], in order to see sails and shipping … so far off that it was two hours before they were seen without my spyglass …, for the effect of my instrument is such that it makes an object fifty miles off appear as large as if it were only five miles away…. The Senate, knowing the way in which I had served it for seventeen years at Padua, … ordered my election to the professorship for life.89
He improved his telescope until it magnified objects a thousand times. Turning it to the sky, he was amazed to discover a new world of stars, ten times as many as had yet been catalogued. Constellations were now seen to contain a great number of stars invisible to the unaided eye; so the Pleiades were seen to be thirty-six instead of seven and Orion eighty instead of thirty-seven, and the Milky Way appeared not as a nebulous mass but as a forest of stars great or small. The moon was no longer a smooth surface, but a corrugation of mountains and valleys; and the vague illumination of its unsunned half could be explained as partly due to sunshine reflected from the earth. In January 1610 Galileo discovered four of the nine “moons” or satellites of Jupiter; “these new bodies,” he wrote, “moved around another very great star, in the same way as Mercury and Venus, and peradventure the other known planets, move around the sun.”90 In July he discovered the ring of Saturn, which he mistook for three stars. Critics of Copernicus had argued that if Venus revolved around the sun it should, like the moon, show phases—changes in illumination and apparent shape; and they had held that there was no sign of such changes. But in December Galileo’s telescope revealed such phases, and he believed that they could be explained only by the planet’s revolution around the sun.
It seems unbelievable, but Galileo, in a letter to Kepler, affirmed that the professors at Padua refused to credit his discoveries, refused even to look at the skies through his telescopes.91 Tiring of Padua, and hoping for a better intellectual climate in Florence (which was passing from art to science), Galileo named the satellites of Jupiter the Sidera Medicea after Cosimo II, Grand Duke of Tuscany. In March 1610 he dedicated to Cosimo a Latin treatise, Sidereus nuncius, summarizing his astronomical revelations. In May he wrote to the Duke’s secretary a letter warm with the ardor and pride of Leonardo’s appeal to the Duke of Milan in 1482. He listed the subjects that he was studying and the books in which he hoped to describe his results, and he wondered if he might secure from his master an appointment that would require less time for teaching and leave more for research. In June Cosimo named him “First Mathematician of the University of Pisa, and First Mathematician and Philosopher to the Grand Duke,” with an annual salary of a thousand florins, and without obligation to teach. In September Galileo moved to Florence, without his concubine.
He had insisted on the title of philosopher as well as mathematician, for he wished to influence philosophy as well as science. He felt as Ramus, Bruno, Telesio, and others had done before him, as Bacon was urging in this same decade, that philosophy (which he understood as the study and interpretation of Nature in all its aspects) had gone to sleep in the lap of Aristotle, and that the time had come to escape from these forty Greek volumes and look at the world with loosened categories and open eyes and mind. Possibly he trusted too much to reason. “To demonstrate to my opponents the truth of my conclusions, I have been forced to prove them by a variety of experiments, though to satisfy myself alone I have never felt it necessary to make many.”92
He had the pride and pugnacity of an innovator, though at times he spoke with a wise modesty—”I have never met a man so ignorant that I could not learn something from him.”93 He was an ardent controversialist, skilled to spear a foe on a phrase or roast hi
m with burning indignation. In the margin of a book by the Jesuit Antonio Rocco defending the Ptolemaic astronomy, Galileo wrote, “Ignoramus, elephant, fool, dunce … eunuch.”94
But that was after the Jesuits had joined in condemning him. Before his encounter with the Inquisition he had many friends in the Society of Jesus. Christopher Clavius confirmed Galileo’s observations with his own; another Jesuit lauded Galileo as the greatest astronomer of the age; a commission of Jesuit scholars, appointed by Cardinal Bellarmine to examine Galileo’s findings, reported favorably on all points.95 When he went to Rome in 1611 the Jesuits entertained him at their Collegium Romanum. “I stayed with the Jesuit fathers,” he wrote; “they had verified the actual existence of the new planets and had been constantly observing them for two months; we compared notes, and I found that their observations agreed exactly with my own.”96 He was welcomed by dignitaries of the Church, and Pope Paul V assured him of his unalterable good will.97
In April he showed to prelates and scientists in Rome the results of observations that revealed spots on the sun, which he interpreted as clouds. Apparently unknown to Galileo, Johannes Fabricius had already announced their discovery in De maculis solis (Wittenberg, 1611) and had anticipated Galileo’s conclusion that the periodicity of the spots indicated the rotation of the sun. In 1615 Christoph Scheiner, Jesuit professor of mathematics at Ingolstadt, addressed to Markus Welser, chief magistrate of Augsburg, three letters in which he claimed to have discovered the spots in April 1611. Galileo, back in Florence, received from Welser a copy of Scheiner’s communications. He discussed them in Three Letters on the Solar Spots, published at Rome by the Accademia dei Lincei in 1613. He claimed that he had observed the spots in 1610 and had shown them to friends in Padua. In the clash of claims to priority in discovering the spots, the friendship between Galileo and the Jesuits cooled.
Convinced that his findings could be explained only on the Copernican theory, Galileo began to talk of the theory as proved. The Jesuit astronomers had no objection to considering it as a hypothesis. Scheiner sent his objections to the Copernican view to Galileo, with a conciliatory letter. “If you wish to advance counterarguments,” he wrote, “we shall in no way be offended by them, but will, on the contrary, gladly examine your arguments in the hope that all this will assist in the elucidation of the truth.”98 Many theologians felt that the Copernican astronomy was so clearly incompatible with the Bible that if it prevailed the Bible would lose authority and Christianity itself would suffer. What would happen to the fundamental Christian belief that God had chosen this earth as His human home—this earth now to be shorn of its primacy and dignity, to be set loose among planets so many times larger than itself, and among innumerable stars?
3. On Trial
Galileo met the problem uncompromisingly. “Inasmuch as the Bible,” he wrote to Father Castelli (December 21, 1613), “calls for an interpretation differing from the immediate sense of the words” (as when it speaks of God’s anger, hatred, remorse, hands, and feet), “it seems to me that as an authority in mathematical controversy it has very little standing. … I believe that natural processes which we either perceive by careful observation or deduce by cogent demonstration cannot be refuted by passages from the Bible.”99 Cardinal Bellarmine was alarmed. Through common friends he sent to Galileo a pointed admonition. “It seems to me,” he wrote to the astronomer’s pupil Foscarini, “that you and Galileo would be well advised to speak not in absolute terms [of the new astronomy as proved] but ex suppositione, as I am convinced that Copernicus himself did.”100
On December 21, 1614, a Dominican preacher, Tommaso Caccini, began the attack, taking as his text an excellent pun, Viri Galilei, quid statis aspicientes in coelum?—”Ye men of Galilee, why stand ye gazing up into the heavens?” (Acts, i, II)—and proceeding to show that the Copernican theory was in irresoluble conflict with the Bible. Other minor warriors sent complaints to the Inquisition; and on March 20, 1615, Cassini lodged a formal accusation against Galileo before the Congregation of the Holy office (the inquisition). Monsignor Dini wrote to Galileo that if he would insert into his publications a few sentences declaring the Copernican view to be hypothesis, he would not be disturbed,101 but Galileo refused, as he put it, to “moderate” Copernicus. In a letter to the Grand Duchess of Tuscany, published in 1615, he wrote with bold clarity: “As to the arrangement of the parts of the universe, I hold the sun to be situated motionless in the center of the revolution of the celestial orbs,V while the earth rotates on its axis and revolves about the sun.”102 He went on to a broader heresy:
Nature … is inexorable and immutable; she never transgresses the laws imposed upon her, or cares a whit whether her abstruse reasons and methods of operation are understandable to men. For that reason it appears that nothing physical which sense-experience sets before our eyes, or which necessary demonstrations prove to us, ought to be called in question (much less condemned) upon the testimony of Biblical passages which may have some different meaning beneath their words.
However, he promised submission to the Church:
I declare (and my sincerity will make itself manifest) not only that I mean to submit myself freely and renounce any errors into which I may fall in this discourse through ignorance of matters pertaining to religion, but that I do not desire in these matters to engage in disputes with anyone…. My goal is this alone: that if, among errors that may abound in these considerations of a subject remote from my profession, there is anything that may be serviceable to the holy Church in making a decision concerning the Copernican system, it may be taken and utilized as seems best to the superiors. And if not, let my book be torn and burned, as I neither intend nor pretend to gain from it any fruit that is not pious and Catholic.103
But he added, “I do not feel obliged to believe that that same God who has endowed us with sense, reason, and intellect has intended us to forgo their use.”104
On December 3, 1615, he went to Rome of his own accord, armed with friendly letters from the Grand Duke to influential prelates and the Florentine ambassador at the Vatican. In Rome he undertook to convert ecclesiastical officials individually; he upheld the Copernican system at every opportunity; soon “everybody” in Rome was discussing the stars.105 On February 26, 1616, the Inquisition directed Cardinal Bellarmine to “summon before him the said Galileo and admonish him to abandon the said opinions, and in case of refusal … to intimate to him, before a notary and witnesses, a command to abstain altogether from teaching or defending the said opinions and even from discussing them. If he do not acquiesce therein he is to be imprisoned.”106 Galileo appeared before Cardinal Bellarmine on that day and declared his submission to the decree.107 On March 5 the Holy Office published its historic edict:
The view that the sun stands motionless at the center of the universe is foolish, philosophically false, and utterly heretical, because contrary to Holy Scripture. The view that the earth is not the center of the universe and even has a daily rotation is philosophically false, and at least an erroneous belief.108
The Congregation of the Index, on the same date, forbade the publication or reading of any book advocating the condemned doctrines; but in the case of Copernicus’ De revolutionibus orbium coelestium (1543) it forbade the use of the book “until it is corrected”; and in 1620 it allowed Catholics to read editions from which nine sentences that represented the theory as a fact had been removed.
Galileo returned to Florence, lived in studious retirement in his villa, Bellosguardo, and kept out of controversy till 1622. In 1619 his disciple Mario Guiducci published an essay embodying Galileo’s theory (now rejected) that comets are emanations of the earth’s atmosphere, and vigorously criticizing the views of the Jesuit Orazio Grassi. The irate father, under a pseudonym, published an attack upon Galileo and his followers. In 1622 Galileo sent to Monsignor Cesarini in Rome the manuscript of Il saggiatore (The Assayer), answering Grassi, and rejecting, in science, all authority but observation, reason, and experiment. With th
e author’s consent some members of the Accademia dei Lincei softened a few passages. In this form Urban VIII accepted its dedication and sanctioned its publication (October 1623). It is Galileo’s most brilliant composition, a masterpiece of Italian prose and controversial skill. The Pope, we are told, enjoyed it; the Jesuits squirmed.
So encouraged, Galileo set out again for Rome (April 1, 1624), hoping to convert the new Pope to Copernican ideas. Urban received him cordially, gave him six long interviews and many gifts, listened to the Copernican arguments, but refused to lift the Inquisition’s ban. Galileo went back to Florence consoled by Urban’s declaration to the Grand Duke, “For a long time we have extended our fatherly love to this great man, whose fame shines in heaven and marches on earth.”109 In 1626 Galileo was heartened by the appointment of his pupil Benedetto Castelli to be mathematician to the Pope, and of another pupil, Father Niccolo Riccardi, as chief censor of the press. He hastened now to complete his chief work, an exposition of the Copernican and anti-Copernican systems. In May he took the manuscript to Rome, showed it to the Pope, and obtained the ecclesiastical imprimatur for its publication, on condition that the subject be treated as hypothesis. Back in Florence, Galileo revised the book and issued it (February 1632) under a long title: Dialogo … dei due massimi sistemi del mundo—Dialogue of G. G., … Where, in Meetings of Four Days, Are Discussed the Two Chief Systems of the World, Ptolemaic and Copernican, Indeterminately Proposing the Philosophical and Natural Arguments, as Well on One Side as on the Other.