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"As fresh and invigorating a work in the field of science biography as was its hero in his day." — Science
"A clear exposition of his discoveries, methods, and experiments…Recommended." — Library Journal
An absorbing account of the origins of modern science as well as a biography of the revolutionary thinker, this inspiring book was co-written by a former director of the Italian Institute for Nuclear Physics and a historian of science (who was also the wife of physicist Enrico Fermi). It begins in Galileo's youth, with his return to his native city of Pisa to train as a physician. Instead, the student became captivated by the power of mathematical reasoning — an interest that led him to apply mathematical logic to natural events and, ultimately, to invent the concept of experimentation. Galileo's progress from student to teacher to scientific innovator is traced, with particular emphasis on his experiments with building and refining telescopes and his unprecedented observations of the moon and planets. The dramatic results of his findings, including his refutation of Aristotelian theory and his support of Copernican doctrine, are related in full, along with his clash with the papal inquisition and his tragic demise under house arrest. Written with a warm appreciation for the wonders of Galileo's achievements and with impeccable scholarship, this book concludes with a survey of the scientist's remarkable legacy. 12 figures. Appendix. Bibliography. Index.
Student in Pisa.
GALILEO GALILEI was born in Pisa on February 15, 1564. But a date has no meaning unless it is related to well-known events, and to build a frame around that distant February day we shall recall some historical facts.
When Galileo was born, only 72 years had passed since Columbus's discovery of America. Not until the next year would Europeans succeed in establishing a settlement in the land that is now the United States, at St. Augustine, Florida. The first successful colony in Virginia was to start in 1607, when Galileo was 43 years old, and the Mayflower was to anchor at Plymouth when he was 56. He was a baby of two months when Shakespeare was born in England, under the reign of Queen Elizabeth.
Italy was divided into many independent states. Both Florence and Pisa were in the Grand Duchy of Tuscany, in the central and western part of Italy, ruled by a Grand Duke of the Medici family. Tuscany, and Florence in particular, had been the center of the Italian Renaissance, the intellectual movement of the fourteenth to the sixteenth century which had ended the rigid, conservative culture of the Middle Ages and prepared the way to the enlightened thought of our modern Western civilization. Evidence of the extraordinary degree to which all the arts had flourished in Florence were its famous palaces, churches, and paintings that many tourists still go to see.
The artistic period of the Renaissance was coming to an end. Only three days after Galileo was born, Michelangelo, the greatest of all Florentine artists, died in Rome. Western civilization, after a long period of joyful expression, of colors and forms, was getting ready for inner thinking, for criticism and science. Although art had reached maturity, science was still in its infancy. The official science, taught by famous teachers in all European universities, studied by thousands of students, still lacked the open-mindedness that had become well established in the arts.
The Galileis were a noble family of Florence who had lost most of their money and had some difficulty making ends meet. Vincenzio, Galileo's father, was an intelligent, well-educated man and an able musician. Not only did he play and teach music, but he also wrote several highly appreciated treatises on the theory of music, some of which are still preserved. In order to make a living, Vincenzio became a cloth merchant and moved temporarily to Pisa, which was then a better trading center than Florence. He and his family returned to Florence when his oldest son, Galileo, was ten years old. He had several other children, some of whom died young, and three of whom we know something about: two daughters, Virginia and Livia, and a son, Michelangelo.
Vincenzio directed Galileo's early education. The boy learned easily and eagerly and must have shown unusual intelligence and alertness, because despite the family's difficult financial condition the father decided that Galileo should go on with his studies at the university. This meant that the boy would live away from home, since the university of the Grand Duchy of Tuscany was in Pisa. If the decision on what to study had been left to Galileo, he would have taken up drawing and painting, he told his friends many years later. But his father had in mind a more remunerative position for him, and so he entered the University of Pisa as a student of medicine.
One of the fundamental courses he was required to take was the philosophy of the great Greek Aristotle, who lived in the fourth century before Christ (384-322 B.C.). In Galileo's time the word "philosophy," which in Greek means "love of wisdom," had a much broader meaning than it has now, and it included the study of all natural phenomena. Aristotle wrote a large number of books in which he presented the entire philosophical and scientific knowledge of his time with a broadness of scope, power of synthesis, and originality that have never been matched. He also founded a school which had many followers and exerted a great influence on the Greek and Latin cultures.
Of the huge bulk of Aristotle's work, Galileo studied mainly the writings on logic, on motion, and on the structure of the universe. In following Galileo's steps, we shall have occasion to show some of Aristotle's views. Here we shall say only a few words about Aristotle's conception of the world.
Many philosophers before Aristotle had speculated about the appearance of the skies—the myriads of fixed stars, the apparently complicated paths of the moving stars (which we now call planets), the relation of our earth to sun and moon. Many had tried to fit what they had seen into coherent systems, often using complicated geometrical and mathematical schemes to explain the motion of celestial bodies.
Aristotle did not believe that mathematics was necessary to explain change and motion. His natural philosophy was quite primitive and strongly influenced by the immediate appearance of phenomena. He saw, for instance, change and deterioration on earth but never in the sun and stars. He did not consider the possibility that change and deterioration might take place in the sun and stars as on the earth but might not be seen because the sun and stars are so distant from our earth. He stated that the sun and stars were perfect and unchangeable.
In Aristotle's universe the earth was at the center and all celestial bodies turned around it, moving on transparent spheres. They moved with uniform circular motion, the most perfect form of motion, according to the ancients. The universe was divided in two regions: a sublunar region, below the sphere on which the moon moved, and an outer region, from the sphere of the moon to that of the fixed stars. In the sublunar region everything was made of four elements: air, water, earth and fire; everything was corruptible and changeable and there could be death and birth. In the outer region, containing the planets and stars, everything was made of ether and was perfect and immutable.
Since Aristotle's time, the science of cosmology and astronomy had of course progressed, but most philosophers still accepted only those results of observation that they could reconcile with Aristotle's system of the universe.
Young Galileo began to study Aristotle's texts diligently, as we learn from some Latin commentaries, Juvenilia, which he wrote while a student at Pisa. As he read, he came gradually to realize that in Pisa he really did not have several teachers but only one teacher, this philosopher Aristotle, who had been dead for 18 centuries. On all questions concerning the study of nature, Aristotle was the source of authority—either in his own writings or in the commentaries of those who had gradually modified or altered the Aristotelian point of view.
Although at first he went along with the trend, Galileo spent most of his adult life in a struggle against the Aristotelian tradition and the men who accepted it blindly. A few words about the meaning of Aristotle's teachings and his authority will help to measure Galileo's stature and to explain the difficulties he faced in breaking from tradition.
Aristotle had a great following in the Greek and Latin worlds, but after the fall of the Roman Empire most of his works were lost to Western civilization and were forgotten for several centuries. Only in the Byzantine world, the cultural heir of ancient Greece, did Aristotle's works survive. They were soon translated from Greek into Syriac, and, after the Arabs conquered Syria, from Syriac into Arabic. In the twelfth and thirteenth centuries these Arab translations, and Arab interpretations of Aristotle's writings, were translated into Latin. In all these wanderings Aristotle's thought had suffered changes and distortions. He would hardly have recognized some of the views attributed to him. Yet it was these dubious versions of his writings that revived Western interest in him.
Shortly afterwards several of Aristotle's Greek texts were found in Constantinople (the ancient Byzantium). Under the impulse of St. Thomas Aquinas, one of the Doctors of the Church, Catholic monks translated them directly from the Greek into Latin. St. Thomas himself studied Aristotle's texts and wrote commentaries which over the centuries profoundly affected the Church's thinking. There were important ideas in Aristotle's works which St. Thomas could not explicitly identify with the religious dogma of the Church, but the harmonious and predetermined construction that Aristotle attributed to the universe found a perfect place among these ideals. St. Thomas gave Christian form to Aristotelian thought. Greek perfection, an abstract, geometrical, and aesthetic idea, was transformed into the perfection of God's works. Natural phenomena, and especially the eternal motion of celestial bodies, became a reflection of such perfection, and their ultimate purpose became that of glorifying God, His will and His inscrutable ends.
Over the years Galileo criticized and refuted many of Aristotle's views. In time he became one of the most relentless demolishers of Aristotle's doctrines, and perhaps the most effective. However, he was neither the first nor the only one in his time, for the sixteenth and seventeenth centuries were characterized, in Europe, by a process of profound revision of natural philosophy. In little less than a century this process changed the image that man had of the universe more fundamentally and rapidly than ever before in history. But even before all this started, some serious criticism had been raised against the solidly established Aristotelian structure. At the University of Paris in the fourteenth century, for instance, the Frenchman Jean Buridan and others had not accepted Aristotle's explanation of motion. We know that the motion of a body originally at rest is caused by forces. To the Greek philosopher a force (or more precisely the cause of velocity) could not be separated from a being, man or God, who somehow perceived its intensity. Aristotle also believed that things moved only when a force acted on them; that if the action of a force was not evident on a body in motion it was because the particles of surrounding air propagated and maintained this action: When a body received a push it started to move, leaving a vacuum behind; into this vacuum rushed particles of air pressing the body on, because nature, as most ancients believed, "abhors a vacuum." Buridan tried to find a more rational explanation of motion, and in this he was one of the most eminent among Galileo's precursors.
Any uncritical acceptance of one man's opinions was not consistent with Galileo's independent spirit and the broad-minded education he had received at home. His father, Vincenzio, was a man of liberal views and was used to expressing them openly. At about the time Galileo entered the university, Vincenzio published a Dialogue of Ancient and Modern Music in which he made one of his characters say: "It appears to me that they who in proof of any assertion rely simply on the weight of authority, without adducing any argument in support of it, act very absurdly. I, on the contrary, wish to be allowed freely to question and freely to answer you without any sort of adulation, as well becomes those who are in search of truth."
The perceptive son of a man who could write this way was bound gradually to realize that his teachers in Pisa acted exactly in the manner that his father considered absurd. There were in Pisa, as in other European universities, a great rigidity and a mental inertia that may now seem surprising. They were especially noticeable in anything concerning science, including medicine, which was then mixed and confused with philosophy, theology, and astrology. The bold freedom of thought of the Renaissance had remained within the vast but definite limits of magnificent works of art. It had not yet surmounted the barrier of the traditional philosophy, which had by then become strongly tied to religious belief.
Trends weakening these barriers started to appear in the sixteenth century as a natural consequence of the Renaissance intellectual innovations. Young Galileo, being the son of a man who was both a musician and a mathematician, must have been especially sensitive to these new trends and receptive to innovations. Since his very respectable teachers provided no innovations, he read directly in "this immense book that nature keeps open before those who have eyes in their forehead and brains."
And thus he made his first discovery, according to his most devoted pupil and earliest biographer, Vincenzio Viviani (1622-1703). But in relating episodes of his teacher's life, Viviani, who met Galileo only when Galileo was already a very old man, often embellished them, and so he may have done when he described the first discovery his old teacher had made when a young student. Yet this story is of great significance.
SWINGING LAMPS AND PENDULUMS
One day in the Cathedral of Pisa, says Viviani, Galileo was watching a lamp which had been moved from its rest position and was swinging from the ceiling. Probably guided by his musical education, he observed a rhythm in the swings of the lamp. It seemed to him that the lamp always took the same time to go from one end of its swing to the other, although its successive swings were gradually decreasing in amplitude. The reason for this, he thought, could be that the greater velocity of the lamp during the first swing made up for the longer path which it had to travel. How could he find out whether all swings actually took the same time?
He thought of measuring the times of swings. But there were no wrist watches then, and had a clock been available it would have been of little help, because clocks were not accurate enough to measure short times. Galileo, the student of medicine, put his finger on his pulse and counted the beats. Every oscillation of the lamp lasted the same number of beats.
Not satisfied with this proof, he went home—he lived with relatives in Pisa—and tied two small balls to two strings of exactly the same length. He swung one ball a certain distance from the rest position and the other a different distance. While he watched one pendulum, a friend watched the other and they both counted the oscillations. They found that both pendulums made the same number of oscillations in the same time. Even balls of different weight oscillated with the same period, provided they were hung on strings of the same length. Thus Galileo discovered the law of isochronism (equality of time) of small oscillations.
Historians of science have ascertained that the famous lamp in the Cathedral of Pisa, which is still called Galileo's lamp, was hung three years after he is said to have watched it swing. But it could have been another lamp in the same church. Galileo himself did not leave in writing a description of his earliest experiments. He referred, however, to observations, "especially in churches where lamps, suspended by long cords, had been inadvertently set into motion." Besides, both in a letter of 1602 and in the greatest of his books, Two New Sciences, he described experiments which fit into a part of Viviani's story, without saying when he performed them. In Two New Sciences he says:
"... I took two balls, one of lead and one of cork, the former more than a hundred times heavier than the latter, and suspended them by means of two equal fine threads, each four or five cubits long. Pulling each ball aside from the perpendicular, I let them go at the same instant, and they, falling along the circumferences of circles having these equal strings for semi-diameters, passed beyond the perpendicular and returned along the same path. These free goings and returnings repeated a hundred times showed clearly that the heavy body maintains so nearly the period of the light body that neither in a hundred swings nor even in a thousand will the former anticipate the latter by as much as a single moment, so perfectly do they keep step."
Clearly, in this crude experiment these two pendulums could not have kept perfect step in "a thousand swings." In other experiments also Galileo claims more precise results than he could have obtained with his apparatus. But Galileo had a remarkable ability to judge the effects of unessential factors on the results of his experiments: resistance of air and friction of the string would stop a pendulum like Galileo's long before it had made "a thousand swings." Galileo knew that if the resistance of air and friction were removed, if all experimental conditions were ideal, the pendulum would perform "a thousand swings" all lasting the same time. (His "a thousand times" may mean "many times"—in Italian the word mille [thousand] is still used in the sense of "many.")
Excerpted from Galileo and the Scientific Revolution by Laura Fermi, Gilberto Bernardini. Copyright © 2003 Dover Publications, Inc.. Excerpted by permission of Dover Publications, Inc..
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|Introduction: Galileo ... Who was he?||7|
|Observer of Nature|
|Inventor of Experiments|
|Builder of Instruments|
|Defender of Free Thought|
|1.||Student in Pisa||11|
|Swinging Lamps and Pendulums|
|From Medicine to Mathematics|
|2.||The Young Teacher||21|
|Archimedes and the Hydrostatic Balance|
|Teacher in Pisa|
|De Motu (on Motion)|
|From Pisa to Padua|
|A Venetian Nobleman: Sagredo|
|The Experimental School of Medicine in Padua|
|Public and Private Teaching|
|Galileo's Geometric and Military Compass|
|An Unfortunate Trip|
|The Sun at the Center of the Universe|
|News of a Telescope|
|Galileo Presents His Telescope to the Doge|
|5.||The Universe Through the Telescope||48|
|New Aspects of the Moon|
|The Phases of Venus|
|The Aristotelian Universe is Shaken|
|Galileo and Kepler|
|6.||Florence and Rome||62|
|Triumph in Rome|
|The Laws of Nature and the Scriptures|
|The Decree Against the Copernican Doctrine|
|7.||Galileo and Urban VIII||78|
|The Summons to Rome|
|8.||Father and Daughter||86|
|Galileo at Home|
|Sister Maria Celeste|
|Death of a Daughter|
|9.||The Last Years||94|
|The Law of Inertia|
|More About Falling Bodies|
|The Motion of Projectiles|
|Faith in the Laws of Nature|
|"This Vast and Most Excellent Science"|
|Appendix||The Little Balance and a Note on It||113|