Galileo Galilei(1564 1642)




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Galileo Galilei(1564 – 1642)
To put Galileo into historical perspective, we would link him to the following: The famous artist, Michelangelo, died the same month in which Galileo was born, William Shakespeare was born in 1564, Columbus discovered America 72 years earlier and Galileo was 56 when the Mayflower carried the Pilgrims to New England.
The state of science at the time of Galileo was rather static and had not changed much in over 1000 years. Science was based almost entirely on the work of the Greek, Aristotle. His works were lost, rediscovered and translated from Greek to Roman. The major flaw in Aristotle’s work was that it held that the truth about the physical world could be learned by pure thought (philosophy) without testing or experimentation. This type of reasoning led to the idea that a heavier object would fall faster than a lighter object over the same distance. Aristotle also believed that the planets, Sun and stars were all perfect and unchanging and all whirled around the Earth in perfectly spherical orbits. The Earth was not only the center of the solar system, but also the center of the universe. Understandable for the time, but wrong. At the time of Galileo the Catholic Church had control of the all the old Greek and Roman translations of Aristotle and to question these works was considered an act of heresy.
Such was the state of natural philosophy (science) at the time of the young Galileo. Some pamphlets and other works not controlled by the church began to surface. The letters of Tycho Brahe and Nicholas Copernicus began to question the “party line”. Galileo had a good role model in his father, Vincenzio, who was a professional musician and interested in mathematics. Vincenzio wrote, “It appears to me that they who in proof of an assertion rely simply on the weight of authority, without adducing any argument [that is, experimental evidence] in support of it, act very absurdly”. Galileo was brought up to question authority and learn the real nature of the world for himself.
In 1581 Galileo was enrolled in medical school at the University of Pisa. Around this time he purportedly watched a chandelier swing in a pendulum type motion in the cathedral. He used his pulse to time the swings of pendulum (chandelier) and he noticed that each swing took the same time to complete, whether it followed a long arc path or a short one.

He ran home and constructed pendulums of different lengths, which later became the pulsilogia used by doctors to time pulses (although a friend of his actually invented the device). Galileo became Professor of Mathematics at the University of Pisa in 1589. Here he had live-in students (usually quite wealthy) who, when they returned to their homes, sang the praises of their great teacher, Galileo.


Galileo was a great note taker and at the time of his work as a math professor at Pisa had the draft of a book called, “On Motion”. He decided against publishing this book. About this time he, as legend has it, he performed is famous experiment of dropping cannonballs of different weight from the Leaning Tower of Pisa. These balls struck the ground at the same time (about). Some other Aristotelian-type supposedly tried the same experiment and found that the heavier ball hit 2 inches before the lighter ball. Galileo’s reply, ”Aristotle says that a hundred-pound ball falling from a height of a hundred cubits hits the ground before a one- pound ball has fallen one cubit. I say they arrive at the same time. You find, on making the test, that a larger ball beats the smaller one by two inches. Now, behind those two inches you want to hide Aristotle’s ninety-nine cubits and, speaking only on my tiny error, remain silent about his enormous mistake.”
Galileo was now capable of wit, sarcasm and incredible scientific arguments. In 1604 Galileo became and astronomer as a result of the appearance of a new star that we would today call a supernova. He lectured about this “star” as proof that the celestial sphere was not perfect and unchanging(as proposed by Aristotle). He showed that the experimental method was superior to the method of abstract philosophy. The telescope was invented by Hans Lippershey of Holland or maybe even earlier by Leonard Digges of England before 1550. Galileo began to work arduously to build his own telescope. He used one concave and one convex lens in his tube, unlike the others with two convex lenses. This gave an upright image. He got 10 power from his first scope. He than proudly demonstrated this instrument. He gave one to the Doge of Venice as a gift. By 1609 he was up to 20 power and used this telescope to discover the four brightest moons of Jupiter in 1610. He also viewed the Milky Way as a cluster of individual stars. He saw that the surface of the Moon (our Moon) was rough and not smooth.

He began to gain favor, but at the same drew the attention of, the Cardinals and even the Pope in the Vatican in Rome. He purposely stayed away from Rome due to the doctrine of Aristotle being the belief of choice there. He observed Sunspots and correctly observed them as surface phenomenon and orbiting objects, as some contended. In 1615 Galileo visited Rome and was in the Tuscan Ambassador’s residence when the word came down from the Papacy that the Sun centered solar system and the idea that the Earth moved through space were both wrong and heretical. Galileo was officially notified of this position in 1616. Galileo was warned not espouse his beliefs and Galileo returned to Florence.


Time passed and the new Pope in 1621 was favorable to Galileo’s latest book, The Assayer, which went against papal dogma, and was published in 1623. It seemed that the new Pope, Urban VIII, would not try to harass Galileo for his “heretical” ideas. Galileo dedicated the book to the Pope. In this book many of his inertia experiments on inclined plans was revealed and the idea of “idealized motion” was brought forth. It was very profound for a scientist to propose an idealized world where no outside forces acted on the balls on the ramps. This of course helped to establish what these outside forces were and how they changed the ideal motion of the objects. He completed his next book, “Dialogue Concerning the Two Chief Systems of the World”. In the book he cleverly has two characters debate Aristotelian and Galilean points of view on topics with the addition of an outside independent observer. The book awaited the approval of the Vatican sensors who just made small changes and demanded a preface which emphasized the theoretical nature of the debate in the book. Finally, the book was published in Florence in 1632 (1000 copies). A copy was sent to the Vatican in Rome.
In 1633 Galileo went off to be tried for heresy in Rome. The details leading up to this change of heart by the Pope can be studied later. To make a long story short, a plea bargaining session in which Galileo would recant his beliefs for a reduced sentence failed. He was sentenced to life imprisonment (he was 70 at the time). Three Cardinal refused to sign the sentencing document. This was a type of house arrest and Galileo served it in three residences, including his own. His greatest work, “Two New Sciences” was smuggled out of Italy and published in Leyden in1638. Galileo was blind by this time and was not able to read his own book. He described a pendulum clock to his son and this clock was built and used by many after his death in 1642.
I would recommend two books (there are many more) to the reader:

Galileo’s Commandment by Edmund Blair Bolles(published in the US by W. H. Freeman, New York in 1997) and Galileo, In 90 minutes by John and Mary Gribbin (Published by Constable and Company Limited, London in 1997)


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