galileo’s book -- 10/11/23

Today's selection -- from A Little History of Science by William Bynum. Galileo thought he could get away with conveying his radical ideas about the sun and the earth if he couched them carefully in the innocent context of a book he titled Dialogue on the Two Chief World Systems:

“[Galileo saw that] the sun had dark areas or spots, which moved a bit each day in regular patterns. (He learned to look at it indirectly, to protect his eyes, as you must.) His telescope revealed that the Milky Way, which appears as a wonderful, fuzzy blur of light when looking with the naked eye on a clear night, was actually composed of thousands and thousands of individual stars, very far away from the earth. 

“With his telescope, Galileo made these and many other important observations. He wrote about them in a book called Starry Messenger (1610), which created a stir. Each revelation called into question what people thought about the heavens. Some thought Galileo's ideas were based on tricks played by his new 'tube: as the telescope was often called, because what could not be seen by the naked eye might not be there. Galileo had to try to convince people that what his telescope showed was real. 

“Much more awkwardly, and dangerously, was that Galileo's observations were good evidence for Copernicus being right about the moon revolving around the earth, and about the earth, moon and the other planets all orbiting around the sun. By this time, Copernicus's book had been in print for almost seventy years, and he had a number of followers, Protestants as well as Catholics. The official position of the Catholic Church was that Copernicus's ideas were useful to work out the movements of the planets, but they were not literally true. If they were, too many passages from the Bible would be complicated, and have to be thought about again. 

“But Galileo wanted to tell people about his astronomical findings. He went to Rome in 1615 hoping to get the Church's permission to teach what he had learned. Many people -- even the Pope -- sympathised with him, but he was still forbidden to write out, or teach, Copernicus's system. He didn't give up entirely, going to Rome again in 1624 and 1630 to test the waters, though he was getting old and unwell. He became convinced that as long as was careful to present the Copernican system only as a possibility then he would be safe. His work on astronomy, Dialogue on the Two Chief World Systems, is written as a conversation between three people: one representing Aristotle, another representing Copernicus, and the third acting as the host. That way, Galileo could discuss the pros and cons of old and new ideas about the universe without having to say which was right or wrong.

Frontispiece and title page of the Dialogue, 1632

“It is a wonderful book, full of jokes, and written, like most of Galileo's works, in his native language, Italian. (Scholars from all over Europe still usually wrote their books in Latin.) From the start, it was pretty obvious which side Galileo was on. For one thing, the Aristotelian character was named Simplicio. Now, there was in fact an ancient commentator on Aristotle called that, but just as in English, in Italian it sounds like 'simpleton', and this character isn't very bright. The Copernican (called Salviati, a name that suggests 'wise' and 'safe') has by far the best lines and arguments.

“Galileo tried very hard to get the Church's official approval for his book. The censor in Rome, who controlled which books could be published, was sympathetic to Galileo, but he knew there would be problems and so delayed his decision. Galileo went ahead and had the book printed in Florence. When the high churchmen in Rome read it, they were not pleased, and summoned the old man to Rome. Someone dug out a copy of the old ban against him teaching the Copernican system, and after a 'trial' in 1633 that went on for three months, Galileo was forced to say his book was an error and the product of his vanity. The earth, he said in his signed confession, does not move and is the centre of the universe. There is a legend that immediately after being convicted, Galileo muttered, 'Eppur si muove' ('And yet it moves'). Whether or not he did say it out loud, he certainly thought it, for the Church could not force him to change his beliefs about the nature of the world.

“The Church had the power to throw Galileo in prison and even torture him, but his jury recognised that he was a very unusual man, and put him under house arrest instead. His first 'house arrest' in the city of Siena wasn't all that strict -- he was the life and soul of many dinner parties -- so the Church insisted that he return to his home outside Florence, where his visitors were carefully policed. One of Galileo's daughters (a nun) died soon after, and his last years were lonely. But he continued his work, returning to the problems of falling objects and the forces that produce the kinds of movement we see around us every day. His great work, Two New Sciences (1638), is one of the foundations of modern physics. He looked again at the acceleration of falling bodies, and used mathematics to show that acceleration could be measured in a way that anticipated Isaac Newton's later famous work on gravity. He also offered a new way of thinking about the paths of things shot through the air, like cannon-balls, showing how it could be predicted where they would land. With this work, the concept of 'force' -- what influences something to move in a particular way -- took its place in the study of physics."



William Bynum


A Little History of Science


Yale University Press


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