The Story of Western Science

by Susan Wise Bauer

  Ironically, in this one area Harvey was forced to use the same kind of reasoning he had deplored in Galen. He suggested that there must be tiny, threadlike connections between the veins and the arteries, too small for his eyes to see.

  This turned out to be the case; the capillaries were finally viewed, with the help of new microscopic technology, by the Italian physician Marcello Malpighi in 1661, just four years after Harvey’s death. But even in the absence of this one particular proof, the theory of the motion of the heart and the circulation of the blood lined up, in every other way, with the visual evidence provided by dissection.

  To the end of his life, Harvey kept demonstrating the truth of his system, and kept experimenting to make absolutely sure that his criticisms of Galen were just. When he was in his seventies, he was still piling up the evidence. In March of 1651 he wrote to a friend that he had “lately tried” a new experiment in which he had tied off the right chamber of the heart of “a man who had been hanged” and forcibly filled it with water. The result was simple: “not a drop of water or of blood made its escape” into the left ventricle. Galen’s pores did not exist.11

  “You may try this experiment as often as you please,” Harvey’s account of this experiment concludes. “The result you will still find to be as I have stated it.” Replicable, experimental proof had been used to create an entirely new theory of the body; the ancient authority of Galen had been dethroned.

  To read relevant excerpts from De motu cordis, visit http://susanwisebauer.com/story-of-science.

  WILLIAM HARVEY

  De motu cordis

  (1628)

  The original English translation of 1653 has been republished as a Dover paperback, along with the accompanying essay De circulatione sanguinis. The language is slightly archaic but still readable.

  William Harvey, The Anatomical Exercise, ed. Geoffrey Keynes, Dover Publications (paperback, 1995, ISBN 978-0486688275).

  The widely read nineteenth-century translation by Robert Willis is available as a free e-book, as “An Anatomical Disquisition on the Motion of the Heart and Blood in Animals.”

  Robert Willis, trans., The Works of William Harvey, M.D., Sydenham Society (e-book, 1847, no ISBN).

  It has also been reprinted in paperback by Prometheus Books.

  William Harvey, On the Motion of the Heart and Blood in Animals, trans. Robert Willis, Prometheus Books (paperback, 1993, ISBN 978-0879758547).

  TEN

  The Death of Aristotle

  The overthrow of ancient authority in favor of observations and proofs

  We do have in our age new events and observations

  such that, if Aristotle were now alive, I have no doubt he

  would change his opinion.

  —Galileo Galilei, Dialogue concerning

  the Two Chief World Systems, 1632

  When twenty-one-year-old William Harvey arrived in Padua to study at the School of Medicine, Galileo Galilei was already ensconced there as professor of mathematics.

  Galileo, fourteen years Harvey’s senior, was a wildly popular lecturer; he was forced to use the university’s largest hall, seating two thousand, to accommodate the students who came from all over the continent to hear him. But we have no record that Harvey attended. “Mathematics” was a wide term, and Galileo’s lectures were expected to encompass arithmetic, geometry, astronomy, physics, and the arts of military fortification and engineering. These were subjects that did not necessarily cross Harvey’s curriculum; medical education, then as now, tended to be both intense and narrow.1

  Galileo had come to Padua after three unhappy years at the University of Pisa. He had become increasingly critical of Aristotelian physics, and his opinions had not endeared him to the traditionalists at Pisa. When he tactlessly evaluated a dredging machine designed by a university patron as “useless” (and demonstrated just how badly the proposed model would perform), the embarrassed inventor joined the ranks of his enemies.2

  So Galileo was quick to accept the post at Padua when it was offered to him in 1592. But Pisa had not been a waste of time. While there, he had written and circulated an unpublished set of essays on force and motion, De motu, which made a first step toward solving the knottiest problems of the Copernican system.

  Galileo himself was not, at this point, particularly focused on the skies. His concerns lay closer to the earth. Later in his life, he wrote that he had begun to doubt Aristotelian physics when he saw large hailstones and small ones hitting the ground side by side. According to Aristotle, this could happen only if all of the large hailstones fell from higher up, because large objects fall faster than small ones. (Objects that fall do so because they seek their “natural place”—for objects made of “heavy” elements, the center of the universe. Large objects, because they contain a greater concentration of heavy elements, fall faster than small objects.)3

  Galileo could not believe that all of the large hailstones were falling from farther up in the sky. And the essays in De motu show that, while at Pisa, he had carried out a series of experiments and demonstrations that clearly contradicted Aristotle’s physics of motion.

  Nearly seventy years later, the first biography of Galileo—written by the Italian mathematician Vincenzo Viviani, who had served as the old man’s student assistant—insisted that Galileo had disproved Aristotle by repeatedly dropping unequal weights “from the height of the Leaning Tower of Pisa” and watching them hit the ground simultaneously. Viviani’s biography is filled with errors of time and place, casting considerable doubt on this dramatic account. But, as Stillman Drake points out in his classic study of Galileo’s thought, it is quite likely that Galileo carried out public demonstrations so that his Pisan students could see the proofs of his studies with their own eyes. He believed, firmly, that the truth could always be demonstrated. “Truth . . . is not so deeply concealed as many have thought,” he wrote in Chapter 9 of De motu. “[It] is shown to us by Nature so openly and clearly that nothing could be plainer or more obvious.”4

  10.1 GALILEO’S EXPERIMENT

  Yet Galileo lived in a world where this Baconian method—the demonstration of truth through repeated experimentation—was still junior to received authority, still secondary to tradition. Forty years later, Galileo would write scathingly of a Venetian philosopher who attended a public dissection, carried out by a celebrated anatomist who intended to disprove Aristotle’s insistence that all nerves originated in the heart:

  The anatomist showed that the great trunk of nerves, leaving the brain and passing through the nape, extended on down the spine and then branched out through the whole body, and that only a single strand as fine as a thread arrived at the heart. Turning to [the philosopher], on whose account he had been exhibiting and demonstrating everything with unusual care, he asked this man whether he was at last satisfied and convinced that the nerves originated in the brain. . . . The philosopher, after considering for awhile, answered: “You have made me see this matter so plainly and palpably that if Aristotle’s text were not contrary to it, stating clearly that the nerves originate in the heart, I should be forced to admit it to be true.”5

  Seeing was not yet believing.

  Galileo did not publish De motu, most likely because he had not found satisfactory answers to some of his most central questions. But he continued to look. Some fifteen years after his arrival in Padua, he learned of a new tool that could extend the range of his eyes; the spectacle maker Hans Lippershey, practicing his craft in the Netherlands, had put together the convex lenses he used to correct farsightedness and the concave lenses that aided the nearsighted, creating a new instrument. On October 2, 1608, Lippershey asked the Dutch legislature, the States General, to grant him patent protection for this “telescope.”6

  The States General bought a telescope from Lippershey but refused to give him a patent, and within a year telescopes were being assembled all over Europe. Galileo seems to have first encountered a telescope while visiting Venice, sometime in 1609, and upo
n returning home he immediately set to work grinding his own lenses and improving the instrument’s refraction.

  Lippershey’s instrument was only slightly more useful than the naked eye; Galileo managed to refine the magnification to about 20X. Barely a year after his first glimpse through a telescope, he published a study of the skies based on his observations. “The Sidereal [‘starry’] Messenger, unfolding great and marvellous sights,” the frontispiece read, “respecting the Moon’s Surface, an innumerable number of Fixed Stars, the Milky Way, and Nebulous Stars, but especially respecting Four Planets which revolve round the Planet Jupiter at different distances and in different periodic times, with amazing velocity.”7

  Through his telescope, Galileo had seen mountains and valleys on the moon, many more stars than could be seen with the eye alone, and nebulae—cloudy heavenly bodies made up of clusters of individual stars. But the four planets orbiting Jupiter were, in his words, “the matter . . . most important in this work.” They had never before been seen; at first, Galileo had thought them to be newly visible fixed stars, but when he looked at them again on the following day, they had moved.

  10.2 GALILEO AND JUPITER. A REPRODUCTION OF THE SKETCH GALILEO MADE OF HIS TELESCOPIC OBSERVATIONS OF JUPITER.

  And they kept moving, in and out of sight, to the left and to the right of Jupiter itself. Over the course of a week, Galileo was able to sketch out their progression and come to an inevitable conclusion: “They perform their revolutions about this planet . . . in unequal circles.” Galileo’s observations provided unequivocal proof that not all heavenly bodies revolve around the earth. And in the months after publication of The Sidereal Messenger, Galileo used his telescope to observe the changing phases of Venus—inexplicable in the Ptolemaic system, making sense only if Venus were, in fact, traveling around the sun.8

  Aristotelian physics, already dealt a mortal blow by Galileo’s experiments with weights, had been administered a coup de grâce. But the corpse still had its loyalists. The chief philosopher at Padua, an Aristotelian named Cesar Cremonini, simply refused to look through Galileo’s telescope: “What do you say of the leading philosophers here,” Galileo wrote bitterly to the astronomer Johannes Kepler, “to whom I have offered a thousand times to show my studies, but who, with the lazy obstinacy of a serpent who has eaten his fill, have never consented to look at the planets, or moon? . . . To such people . . . truth is to be sought, not in the universe or in nature, but (I use their own words) by comparing texts!”9

  An epic battle was shaping up: between ancient authority and present observation, Aristotelian thought and Baconian method, text and eye. Galileo himself had no quarrel with Aristotelian logic or philosophy, but he refused to take the great man’s physics for granted. Later, in Dialogue concerning the Two Chief World Systems, he put the objections of his opponents in the mouth of his tradition-bound character Simplicius: “If Aristotle is to be abandoned, whom should we have for a guide?” asks Simplicius. “We need guides in forests and in unknown lands,” responds Galileo’s spokesman in the dialogue, the scholar Salviati, “but on plains and in open places only the blind need guides.” Philosophy might still be an unknown, thickly wooded place, but in Galileo’s opinion, physics and astronomy were now clear spaces where anyone with wits and eyes could see the truth; the earth had been “lifted up out of darkness and exposed to the open sky.” Aristotle himself, he argued, would have appreciated the new discoveries—and would have been willing to adjust his physics accordingly.10

  But Aristotle’s adherents did not agree. And they included not just philosophers and scholars (who had no power to do anything but dissent), but also the churchmen who were in charge of the Inquisition, which had a great deal of power indeed.

  By the beginning of the seventeenth century, the theology of the church centered at Rome had been thoroughly Aristotelianized. Thomas Aquinas’s great thirteenth-century synthesis of Christian revelation and Aristotelian metaphysics had infused Roman Christianity. A central element of this synthesis was a careful separation between those things that could be discovered through the exercise of human reason and the use of the senses (such as truths about the natural world) and those realities that could be understood only through divine revelation (such as the nature of God). While this separation might seem to line up nicely with Galileo’s own point of view, it actually introduced a fatal contradiction: the Bible was God’s revelation of himself and so fell into the second category of truth—that which cannot be understood through the senses or through reason. It was a text that must be accepted, not analyzed—much like Aristotle’s own writings.*

  Galileo’s discoveries were doubly troubling: they contradicted both Aristotle and the literal meaning of several biblical passages. And, thanks to the telescope, the movements of the planets could no longer be explained away as a mathematical trick to “save the phenomena.”

  In 1615, Pope Paul V ordered the cardinal Robert Bellarmine to begin a formal investigation of Galileo’s work and its implications. Galileo himself had not yet written anything that explicitly argued the heliocentric position, although his observations in The Sidereal Messenger certainly implied that he accepted it. So, after a year’s sleuthing, Bellarmine recommended that not Galileo’s work, but Copernicus’s On the Revolutions, be placed on the list of heretical, condemned texts (the Index Librorum Prohibitorum). He also warned Galileo, in a private but official meeting, to abandon public agreement with Copernicus.

  In a letter to the Carmelite monk Paolo Antonio Foscarini, who had argued that Copernicus’s system didn’t contradict scripture at all, Bellarmine suggested that the heliocentric model remain a mathematical one alone. “It seems to me,” Bellarmine wrote,

  that [you] and Mr. Galileo are proceeding prudently by limiting yourselves to speaking suppositionally and not absolutely. . . . For there is no danger in saying that, by assuming the earth moves and the sun stands still, one saves all the appearances better than by postulating eccentrics and epicycles. . . . However, it is different to want to affirm that in reality the sun is at the center of the world . . . and the earth . . . revolves with great speed around the sun; this is a very dangerous thing, likely not only to irritate all scholastic philosophers and theologians, but also to harm the Holy Faith by rendering Holy Scripture false.11

  “Speaking suppositionally” would protect both the Bible and Aristotle: a dual victory.

  Bellarmine was not suggesting that telescopic evidence be ignored. Rather, he lacked the mathematics to follow Galileo’s conclusions. As far as he was concerned, heliocentrism had no proof to support it (and, to be fair, Galileo had not yet solved the problem of the earth’s apparent immobility). In fact, Bellarmine was willing to reexamine the matter, should proof be found:

  If there were a true demonstration that the sun is at the center of the world . . . and that the sun does not circle the earth, but the earth circles the sun, then one would have to proceed with great care in explaining the Scriptures that appear contrary, and say rather that we do not understand them than that what is demonstrated is false. But I will not believe that there is such a demonstration, until it is shown me.12

  This declaration rang, in Galileo’s ears, as a challenge. In 1616 he began to circulate a manuscript essay called “On the Tides,” which argued that the movements of the seas could be explained only if the earth were both rotating on its axis and orbiting the sun. His regular correspondent Johannes Kepler—now holding the position of imperial mathematician to the Holy Roman emperor—was simultaneously working out new orbits for the planets that gave the Copernican model even greater accuracy.

  Over the next sixteen years, Galileo tackled the remaining problems of the heliocentric model, one at a time. He came to a satisfactory explanation for the earth’s apparent immobility, using as an analogy the dropping of an object from a ship’s mast: even if the ship moves, the object falls to the base of the mast, every time. He worked on the continuing problems of the tides and the phases of Venus. Finally,
in 1632, he put all of his conclusions into a major work: the Dialogue concerning the Two Chief World Systems, Ptolemaic and Copernican.

  By this time, Bellarmine was some twelve years dead. But the Inquisition was still alive and active, so the Dialogue is framed as a hypothetical discussion—an argument among three friends as to whether the heliocentric, geokinetic model could, theoretically, prove to be the best possible picture of the universe. The Copernican model is defended by the thoughtful and intelligent characters Salviati and Sagredo; all Inquisition-approved opinions are voiced by the least sympathetic character, the clearly ignorant and incompetent Simplicius, blindly loyal to Aristotle, willing to check his reason at the door.

  The ruse was sufficient to get the Dialogue past the initial censor, the Dominican theologian Niccolo Riccardi, although Riccardi insisted on a preface that recognized the church’s perfectly valid objections to heliocentrism. He also wanted a disclaimer at the end cautioning that the tides could be understood without recourse to a moving earth. Galileo promptly supplied a highly sarcastic preface (“Several years ago there was published in Rome a salutary edict which, in order to obviate the dangerous tendencies of our present age, imposed a seasonable silence upon the . . . opinion that the earth moves”), and placed in Simplicius’s mouth an ending assertion that God, “in His infinite power and wisdom,” was probably causing the tides to move “in many ways which are unthinkable to our minds.”13

  The preface seems to have satisfied Riccardi, who was not a sophisticated reader, and in February 1632 a thousand copies of the Dialogue were printed in Florence. The print run immediately sold out. By early spring, churchmen who had better ears for irony than Riccardi were beginning to point out that Galileo had undoubtedly violated Bellarmine’s earlier warning.