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Introductory notes and background

Galileo was born in Pisa on 15 February 1564 (he died in 1642), the oldest of seven children; he in turn was to have three children, two daughters and a son, with his longtime lover, Marina Gamba, whom he never married and from whom he lived apart for most of their relationship.  Galileo’s family had ancient roots in the city of Florence, were well to-do merchants and educated men; his father was a cloth merchant by trade and a musician, composer, and mathematician by calling.  As the oldest son, Galileo's parents sought schooling for him, and in 1581 he matriculated at the University of Pisa where he studied medicine and mathematics.  He much preferred the latter, and studied for four years at Pisa, where he eventually (in 1589) would secure a post as professor of Mathematics.  There he carried out his famous experiment by dropping items of different weight from the "leaning" tower of Pisa in order to disprove Aristotle’s theory that items of different weight will fall at different speeds.  This penchant for experimental proof, as opposed to theoretical or philosophical proof, became his trademark.

In 1591, on the death of his father, Galileo took over financial responsibility for his siblings, and the following year he took a post as professor of Mathematics at the University of Padua, near Venice.  During this time he had two personal events which would influence his life in dramatic ways: he met his lover and partner, Marina Gamba, fathered his children, and fell very ill with a mysterious sickness that would revisit him throughout his life.  Thereafter, periods of professional productivity were interspersed with periods of prolonged illness.  He stayed at Padua from 1592-1610.  During that time, in 1597, he invented his first commercial instrument, a kind of compass that was useful for calculating everything from monetary exchange rates to military artillery measurements, and he pocketed considerable income from it. Concurrently, he was courting the patronage of the most powerful family in Florence, the de'Medici, both by dedicating his compass work to and tutoring the young Prince Cosimo de Medici, the son of the Duke (Ferdinand) and Duchess (Christina).  Cosimo soon became Grand Duke at the age of 21, and Galileo suddenly had direct entrée into the most powerful house in Italy.

In 1609 another invention followed, a perfected spyglass which improved on the existing design of a Dutch prototype—the first working telescope.  He continued to refine the design, ground the glass lenses so they would be still clearer, and then turned his invention onto the surface of the moon.  There he saw a surface of crags, valleys, and craters.  This was shocking, but still more shocking was what he found when he trained his telescope on the "movable stars," or planets: four moons revolving around Jupiter.  In 1610 he published his observations, with drawings, in The Starry Messenger, dedicated to Cosimo.  It sold out immediately and his findings spread like wildfire.  His reputation made, he was appointed a position as Court Philosopher and Mathematician of the Duke, and given a paid lifetime position at the University of Pisa.  He soon observed what he thought, but could not confirm to be, two planets around Saturn—parts of Saturn’s rings.  He also observed sunspots, and published his findings.

Galileo quickly became the public standard-bearer for scientifc rationalism against religious and philosophical tradition.  This was the beginning of the end of Greek and biblical models of the universe, which could not satisfy the new observers, experimenters, and calculators of the sixteenth century.  A half-century earlier, in 1543, the Polish astronomer Nicholas Copernicus had published his De revolutionibus orbium colestium (On the revolutions of heavenly bodies), in which he argued that many of the observations of celestial planetary movement could be better explained by situating the sun at the center of planetary motions and making the earth a moving planet instead of a fixed point at the heart of a perfectly spherical system, which had been the philosophically dominant understanding of the universe for two millennia.  Copernicus’s De revolutionibus introduced order and symmetry into man’s conception of the heavens, and had the effect of displacing man from the center of the universe, at which he had resided, philosophically and theologically, for so long.  The work did not receive widespread publication, but by Galileo's time was being  widely read and was eventually denounced by many (though not all!) Protestant and Catholic authorities.  In 1609, the German astronomer Johannes Kepler (1571-1630) published the Astronomia nova, which went further than Copernicus by resolving the observational problems produced for terrestrial astronomers by insisting that planets followed circular orbits.  He proposed that heavenly bodies moved along elliptical, not circular, courses, and that the sun was not at the center of the orbits but positioned toward one end of the ellipse.  He discovered as well that planetary motion in these elliptical orbits was regular.  This discovery finally overthrew the existing Ptolemaic system of planetary motion.

In 1613, as his fame burgeoned, Galileo's former patroness, the Duchess Christina, began to raise concerns over his arguments and support of the Copernican system.  This led Galileo to write a formal letter to her two years later.  The letter had several aims; one was to silence his detractors and critics, the other was to persuade Christina that his findings did not contravene biblical passages concerning the organization of the heavens.  Like other letters written in his own self-defense, Galileo's Letter to Christina was inflammatory and pugnacious.  It was not formally published until 1636.  Meanwhile, theological opposition to the Copernica universe was growing in Rome.  In 1616, Pope Paul V summoned a panel of eleven theologians to vote on two Copernican propositions, both supported by Galileo:

I.  The sun is the center of the world, and consequently is immobile of local motion (which was deemed heretical);
II.  The earth is not the center of the world, nor is it immobile, but it moves as a whole and also with a diurnal motion (deemed "erroneous of faith," or undermining matters of faith).

Copernicus’s book was suspended and eventually landed on the Index of Prohibited Books; other works defending Copernicus were condemned; and Galileo was summoned before the court and told to stop propounding Copernican ideas as true.  He escaped censure, however, and was able to continue his work unabated.  His publication in 1632 of the Dialogue concerning the Two Chief World Systems, in which the defender of the old Ptolemaic system is crushed in debate by a defender of the Copernican, earned him respect and condemnation by the Inquisition.  He retracted his position under pressure in 1633, but the circulation of his work in Italian reached thousands of eyes.

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Questions for discussion

(1)  One of the central concerns of the Letter is the relationship between textual and received authority--for example, the word of the biblical scriptures--and the authority of observed, scientific conditions, pr physical properties.  How does Galileo defend the latter?  Is he antagonistic to scriptural authority?  If so, to what degree or in what way?  How can scripture say one thing and mean another?

(2)  How can Galileo insist that the Bible never errs, but that all the same it “is often very abstruse, and may say things which are quite different from what its bare words signify”? (p. 181)

(3)  How can a full understanding of the physical properties of things (like planets and stars) deepen, for Galileo, biblical understanding?  Are biblical or traditional authority inherently antagonistic to experiential/scientific authority?

(4)  Take note of some of the ways in which Galileo defends himself from his critics.  What tactics does he use to delegitimize their criticisms and defend his own positions?