GALILEI, Galileo

(1564-1642)

Renowned for his astronomical observations with a telescope, Galileo Galilei also defined the central tenets of a new scientific method followed by others in succeeding centuries. Condemned for heresy in 1633 because of his defense of heliocentricity, he is emblematic, as are few others, of the "scientific revolution" in human thought.

Born in Pisa, Galileo was the son of a respected if impecunious musician, Vincenzio Galilei.* He began his education at a monastery school in Vallom-brosa, but his father withdrew him before he could complete his novitiate. In 1581 he began to study medicine at the University of Pisa, where his attention turned to mathematics and physics. Although he left the university in 1585 without a degree, he continued his scientific work, publishing on the hydrostatic balance in 1586 and the center of gravity in solids three years later. These works led to his appointment as lecturer in mathematics at Pisa in 1589.

Galileo's tenure there proved short-lived. Attacked as an upstart by tradition­alists, he moved to become professor of mathematics at the University of Padua, where he remained for eighteen years in a friendlier intellectual atmosphere. He championed a new physics, disproving Aristotle's long-accepted theory that ob­jects of different weights fall at different speeds. Although accounts of Galileo dropping spheres from the tower in Pisa are colorful stories, they are little more than legendary. Galileo became a proponent of Nicolaus Copernicus's* helio-centricity, writing in support of it to Johannes Kepler* in 1597.

Made aware of the invention of the telescope in 1609, Galileo engaged in the astronomical observations that made him famous. In The Starry Messenger he announced his discoveries of the irregularity of the surface of the moon, the vastness of the Milky Way as an assemblage of stars, and the existence of four satellites orbiting Jupiter. Each was contrary to accepted astronomical theory, tended to support the Copernican system, and drew strong negative reactions. Nonetheless, Kepler strongly endorsed his discoveries in his Reply to the Starry Messenger.

In 1610 Galileo was appointed philosopher to the grand duke of Tuscany in Florence. Within three years Galileo made additional discoveries and mounted a systematic defense of heliocentricity. He observed the oval shape of Saturn and described the phases of Venus. Following his discovery of the existence of spots on the sun, Galileo systematically defended Copernicus for the first time in print in his Letters on Sunspots.

Galileo also initiated the central failure of his career. He refused to engage Kepler's brilliant description of the elliptical motion of the planets around the sun, published already in 1609. Because of this failure, Galileo's empirical work tended only to militate against the ideas of Ptolemy and Aristotle, rather than to support Kepler's discoveries. Throughout his life Galileo clung to the mis­taken notion that planetary orbits had to be circular.

The publication of Galileo's Letters on Sunspots brought him into conflict with the church for the first time. Although Galileo was favorably received by some in the Catholic church, by 1616 Cardinal Robert Bellarmine had declared Copernicanism erroneous and instructed Galileo to avoid open support of it. Galileo entered semiretirement for the next few years until the publication of The Assayer in 1623, a defense of his methods. The work was dedicated to Pope Urban VIII, long a friend to Galileo. The next year Urban gave him permission to publish on the Ptolemaic and Copernican systems, but he prohibited any conclusive findings. Galileo composed his Dialogue Concerning the Two Chief World Systems and published it with the approval of church censors in 1632.

Presented as an intellectual exercise, the book was in fact a thinly veiled yet strident defense of Copernicanism. Immediately celebrated throughout Europe as a tremendous achievement, it also attracted the attention of the church au­thorities. Believing that he had been made a fool, the pope ordered a trial of Galileo in 1633. On the basis of a "new" document from 1616 ordering Galileo not to defend heliocentricity, which Galileo claimed not to remember, he was found guilty of heresy and forced to recant his views. More recently scholars have claimed that the real issue in the trial was Galileo's defense of atomism—a theory of matter that challenged the church's doctrine of the Eucharist. Regard­less, in 1634 Galileo was placed under house arrest at an estate outside Florence. There he wrote his last great work, The Two New Sciences, examining the strength of materials and the mechanics of motion. Completely blind by 1638, Galileo received friends and pupils as visitors until his death in 1642.

Although Galileo is best known for his use of the telescope, the significance of his life and work should be found in his understanding of scientific inquiry and his new method for it. This method stood in contrast to traditional forms of science, which resembled the study of literature, history, and theology. When his defense of Copernicus was attacked as contrary to Scripture, he replied with an eloquent description of the independent realms of science and religion. By 1615 his famous Letter to Grand Duchess Christina argued that neither Scripture nor science could be false. The allegorical truth of biblical passages withstood all new scientific discoveries, and only the natural world was the proper domain of the scientist. His contributions to astronomy, physics, and mechanics were considerable, but his most important legacy stemmed from his method. As had no other scientist before him, Galileo emphasized empirical observation, repro­ducible experimentation, and mathematical modeling as the keys to understand­ing the natural world.

Bibliography

M. Biagioli, Galileo, Courtier, 1993.

P. Redondi, Galileo Heretic, 1987.

J. Reston, Galileo, 1994.

M. Sharratt, Galileo, 1994.

Edmund M. Kern