Shea and Artigas - Galileo in Rome

by William R. Shea

  THE DOCTRINE OF THE EUCHARIST

  To understand the background to this charge, we have to recall that Catholic thought was dominated since 1564 (the year of Galileo’s birth) by the Decrees of the Council of Trent (1545–1563), which were promulgated that year. The Protestant Reformers had tended to emphasize the spiritual, and downplay the literal, meaning of Christ’s words at the Last Supper, “This is my body. This is my blood.” The Catholic bishops present at Trent wished to stress that these words meant that Christ was really present. They did not intend to explain away the mystery of the Eucharist but to offer an interpretation of the presence of Christ that was not merely symbolic, and they expressed this conviction by saying that the substance of the bread and wine become the substance of the body and blood of Christ (what they termed transubstantiation). What is left of the bread and wine are only their appearances such as their color, taste, odor, and so on. A philosophical school to which Galileo was close believed that matter is made up of invisible particles of matter or atoms. On this view, “primary qualities” such as size, shape, and motion are really in the things themselves, but “secondary qualities,” namely colors, tastes, and sounds, are not in the objects but in the organs that respond to the stimulus of the “primary qualities.” In this sense, they can be called subjective. In The Assayer, Galileo had given an atomistic interpretation of the nature of heat, which he described as caused by matter in motion. This view clashed with the common-sense belief that heat is an intrinsic property of bodies. To refute this naive realism, Galileo devised one of his cleverest thought experiments:

  As soon as I think of a material object or a corporeal substance, I immediately feel the need to conceive simultaneously that it is bounded and has this or that shape, that it is big or small in relation to others, that it is in this or that place at a given time, that it moves or stays still, that it does or does not touch another body, and that it is one, few, or many. I cannot separate it from these conditions by any stretch of my imagination. But my mind feels no compulsion to understand as necessary accompaniments that it should be white or red, bitter or sweet, noisy or silent, of sweet or of foul odor. Indeed, without the senses to guide us, reason or imagination alone would perhaps never arrive at such qualities. For that reason, I think that tastes, odors, colors and so forth are no more than mere names so far as pertains to the subject wherein they seem to reside, and that they only exist in the body that perceives them. Thus, if living creatures were removed, all these qualities would vanish and be annihilated.

  When someone tickles you with a feather, the unpleasant sensation you feel is in you. It is not a property of the feather. It is a subjective response to an external stimulus. Likewise, says Galileo, tastes, odors, and colors exist in the organs that are affected by them, not in their causes. The theological problem arises as follows: if color, taste, and other “secondary qualities” are pronounced subjective, might this not imperil the teaching of the Council of Trent on the objective distinction between the real substance of Christ’s body and blood and the equally real properties of bread and wine? A sensitive soul, or perhaps a malevolent colleague, wrote to the Holy Office to draw attention to this latent danger in the interpretation of the consecrated host. Fortunately for Galileo, Cardinal Francesco Barberini, who was a member of the Holy Office, offered to investigate the matter. He entrusted the task to his personal theologian, Giovanni di Guevara, who read Galileo’s work and saw no reason to pursue the matter. “So things calmed down,” writes Guiducci, but Cesi feared it was only the lull before the storm.

  Cesi was proved right when Grassi published a reply to The Assayer in which he raised the very objections that had been made by the anonymous delator. He argued that in the Eucharist the substance of bread and wine is converted into the body and blood of Christ and that what we see are only the remaining accidents, such as whiteness. Now for Galileo these accidents were just names, and Grassi aired the concern that such a view was difficult to reconcile with Catholic teaching. At about that time Cardinal Francesco Barberini was appointed papal legate, or ambassador, to France and left for Paris with Guevara. In their absence, it was doubly wise to avoid stirring the waters. Galileo was not happy, but he saw the point.

  THE TENSION MOUNTS

  Since the summer of 1626 Galileo had another important contact in Rome in the person of Benedetto Castelli, whom Urban VIII had called from Pisa to act as tutor to his nephew, Taddeo Barberini, and to supervise canals and waterworks in the papal states. Castelli was shortly thereafter appointed professor at the University of Rome and spent the rest of his life in the Eternal City. In Pisa, he had acted as tutor to Galileo’s own son, Vincenzio, and Galileo asked him to take care of his nephew, also called Vincenzio, to whom he wanted to transfer the ecclesiastical pension he had obtained from the pope for his own son. The nephew, like his father, Michelangelo Galilei, was said to have musical talent, and Castelli found lodgings and a music teacher for him. Unfortunately, Vincenzio was idle and spendthrift, and he displayed a total disregard for the Church. It was not just that he resented the clerical dress and the set prayers that went with his pension or that he stayed out all night in dubious company. He said openly that he did not see why he should join others in worshipping a piece of painted wall. This insolence alarmed Castelli, especially after Vincenzio’s landlord complained that if he meant those words seriously he would soon be denounced to the local ecclesiastical authorities. The last thing Galileo wanted was a nephew branded as a heretic in Rome, and the scapegrace was made to leave as soon as possible. During this troublesome episode, Castelli offered to introduce Galileo to a newly discovered relief: tobacco. His first mention of it elicited a request for further information, and Castelli waxed eloquent on its therapeutic virtues in a letter of 29 April 1628. As far as we know, Galileo was not convinced, and never took to the weed.

  While writing out his reply to Ingoli, Galileo did not neglect to refurbish his best weapon, the argument about the tides, which he had already circulated in manuscript form between 1616 and 1618. Father Niccolò Riccardi had not seen it and requested a copy through Johann Faber on 14 September 1624. In a letter to Cesi of 23 September 1624, Galileo confirmed that he had returned to the tides and that the thrust of the argument was the following: “If the Earth is at rest, the tides cannot occur, but if it moves with the motions described, they necessarily follow with all that is actually observed.”

  Galileo also worked on perfecting his compound microscope, for which he had had to wait for doubly convex lenses, which were difficult to grind. His letter of 23 September, which accompanied the shipment of such an instrument to Cesi, offers a personal comment on what he had himself seen:

  I have observed many tiny animals with great admiration, among which the flea is quite horrible, the mosquito and the moth very beautiful, and I have seen with great pleasure how flies and other little animals can walk attached to mirrors upside down. You will have the opportunity of observing a large number of such particulars, and I should be grateful if you would let me know about the more curious. In short, the greatness of nature, and the subtle and unspeakable care with which she works is a source of unending contemplation.

  In honor of the Barberini family, bees were given pride of place, and Galileo had the pleasure of seeing how well the Lynceans could use his instrument in a broadsheet that they published in 1625.

  Galileo was also consulted on the new state carriage that Urban VIII wanted to have built, and he seems to have suggested that it should be suspended from 2 springs at the ends rather than be made to rest on one support only. Cardinal Francesco Barberini, who had been entrusted with the decoration of the vehicle, considered painting a sun at the center of the ceiling and placing the twelve signs of the Zodiac around it. Guiducci remarked that this would be in disagreement with the Ptolemaic system. “Of course,” he declares in his letter of 15 October 1624 to Galileo, “I am only joking and I don’t mean it.” Nonetheless, he could not help adding that if the paintin
g were actually executed he would welcome the opportunity of telling the cardinal that it would be prohibited by the Congregation of the Index, and that Ingoli would denounce him. Guidicci was a lawyer and could allow himself a jest, perhaps the last one in the unfolding of this affair. The high drama was yet to come.

  CHAPTER FIVE

  Star-Crossed Heavens

  FIFTH TRIP • 3 MAY-26 JUNE 1630

  Galileo had returned to Florence in the summer of 1624 with the conviction that he was now free to write on the motion of the Earth as long as he avoided stating that it was physically true. Within a couple of months he had finished his Reply to Ingoli and could now return to his Dialogue. To emphasize what he considered his decisive argument for the motion of the Earth, Galileo planned to call the work The Discourse on the Tides. It is only when the pope objected that he changed it to The Dialogue on the Two Chief World Systems. The work is the record of a discussion spread over four days, like a play in four acts, among three friends who meet in a palace in Venice.

  Galileo, who was now over 60, welcomed the opportunity to bring back to life two of his best friends. The first is Filippo Salviati, his host at the Villa delle Selve near Florence, where he had been frequently a visitor. He is Galileo’s spokesman and he makes a brilliant case for Copernican-ism. The second is the Venetian patrician Giovanfrancesco Sagredo, in whose palace the meeting is held. He is presented as open-minded and unprejudiced, but he is already half converted to Copernicanism and plays second fiddle to Salviati. The third participant, an Aristotelian professor called Simplicio, is a completely fictional character, but Simplicius was the name of a sixth-century Greek philosopher who was famous for a commentary on Aristotle. In Italian, Simplicio also sounds like simpleton, and Galileo may have intended the pun. Simplicio is neither very bright nor very well informed and sometimes plays the buffoon who gets kicked in the pants.

  A PHILOSOPHICAL AND LITERARY MASTERPIECE

  It was a basic tenet of Aristotelian philosophy that the heavens are immutable and that change and decay only occur on Earth. This rested on the assumption that heavenly bodies naturally move in perfect and unending circles while bodies on Earth naturally go straight up or straight down. The distinction was important because it implied that the physics that is found on Earth is not applicable to the heavens above. This philosophical bias had to be dismantled, and in the first day of the Dialogue, Galileo chips away at the distinction in order to show that it is no longer plausible to treat the heavens as completely different from the Earth since the telescope has shown mountains on the Moon. Terrestrial physics can and should be extended to the celestial regions argues Salviati, who is careful not to overstate his argument. Sagredo, the voice of sweet reasonableness, points out that plants, animals, and humans could not live on the moon because there is no water there. Nonetheless Salviati does not rule out that the moon could contain creatures very different from us who would praise the Lord in their own way. This left open an issue that will raise eyebrows among theologians. The appearance of supernovae and comets had shown that the heavens are not inalterable, and if the Ancients had been wrong about celestial bodies, might they not have been equally misled about the Earth when they declared that it could not move through space?

  The second day of the Dialogue examines the possibility of the daily rotation of the Earth. Would it not be simpler, asks Salviati, to allow the Earth to rotate from west to east once a day rather than have the whole heavens spin around the Earth at a fantastic speed every 24 hours? The traditional view, chimes in Sagredo, could be compared to climbing a cupola to view the countryside and then expect the landscape to revolve around one’s head. Aristotelians, of course, knew that a rotating Earth would be simpler; they just thought it preposterous.

  The apparent steadiness of the Earth lulled the mind into a false stability and gave rise to such difficulties as the following: If the Earth was moving, the clouds would be blown away and birds could not fly against the constant gale. Worse still, buildings would be flung off the surface of the Earth because the speed of rotation at the equator would be about 1800 kilometers per hour! Or, on a less dramatic note, a stone dropped from a tower would fall not at its foot but slightly to the west because while it was coming down the tower would have moved to the east. The correct answer to these objections is that Earth imparts its global motion to all terrestrial objects. Hence, the air through which birds fly is carried along with the earth. Likewise a stone that is falling shares in the rotation of the Earth just as much as when it is lying on top of a tower. To grasp why we cannot observe that we are rotating, Salviati suggests the following experiment.

  Shut yourself with a friend inside a large windowless cabin on a ship. Flies buzz round the cabin, fish swim in a bowl, and a tap drips water into a basin. While the ship is standing still, the flies move back and forth with the same ease, the fish swim equally well in all directions, and the water drips straight into the bowl. If you throw a ball to your friend you need no more force in one direction than in another. Now let the ship move as fast as you like but in such a way that the motion is uniform and smooth. What will you notice? Nothing. The flies, the fish, the drops of water, and the ball will behave just as they did before because the ship’s motion is shared by everything in the cabin. No experiment performed inside a windowless cabin can show whether the ship is moving or not. In the same way, no tests carried out on Earth can decide whether it is spinning or at rest. Falling bodies, arrows, or cannon balls will follow the same path whether the Earth is stationary or rotating on its axis.

  The third day of the Dialogue deals with the Earth’s annual motion around the Sun in the company of Mercury, Venus, Mars, Jupiter, and Saturn. The planets are all on circular racetracks around the Sun, but since we observe them from a moving Earth they appear to move backwards or forwards as we overtake or pass them. When we catch up with Mars, for instance, it seems to slow down and when we race ahead it appears to move in the opposite (westward) direction for a while until it resumes its eastward motion. The immobility of our world is an illusion. We spin. We speed through space. We circle the Sun. We live on a wandering star.

  The heliocentric system provided a simpler explanation of the motions of the planet, but, however attractive, simplicity is not the last court of appeal in physics. As we have seen, Galileo was convinced that he had found a decisive physical argument for the motion of the Earth in the ebb and flow of the sea, which resulted, according to him, from the combined effect of the daily rotation of the Earth and its annual revolution around the Sun. The fourth and concluding day of the Dialogue is devoted to this idea and was inspired by what Galileo had seen in the barges that carried fresh water from the mainland to Venice. When these barges slowed down, the water piled up in front, and when they accelerated, the water rose at the other end. The seabeds, reasoned Galileo, are large basins of water and the diurnal and annual motions of the Earth combine to speed up their oscillation or slow them down every twelve hours. Local features such as the orientation and configuration of the seabeds or the shore were presumed to account for variations from place to place. The idea was ingenious; unfortunately, it was also false.

  The Dialogue is a great scientific treatise, but it is also a literary masterpiece. Galileo’s style is not characterized by the bare factualness of the modern laboratory report or the unflinching rigor of a mathematical deduction. Words for him are more than vehicles of pure thought. They are sensible entities; they possess associations with images, memories, and feelings. Galileo knew how to use them to attract, hold, and absorb attention. He did not present his ideas in the nakedness of abstract thought but clothed them in the colors of feeling, intending not only to inform and teach but also move and entice to action. Indeed, he wished to bring about nothing less than a reversal of the 1616 decision against Copernicanism.

  SLOW PROGRESS

  During the period 1625–1629, Galileo was frequently interrupted by illness and could do little writing. It is only in the autumn o
f 1629 that he was able to resume his work. He describes his progress to his friend Elia Diodati in a letter of 29 October 1629:

  A month ago I took up again my Dialogue about the tides, put aside for three years on end, and by the grace of God I’m on the right path, so that if I can keep on this winter I hope to complete the work and publish it immediately. Besides the material on the tides, you will find many other problems and a detailed confirmation of the Copernican system with a demonstration of the futility of everything that was objected by Tycho and others.