Galilei, Galileo

SUBJECT AREA: Photography, film and optics

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b. 15 February 1564 Pisa, Italy

d. 8 January 1642 Arcetri, near Florence, Italy

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Italian mathematician, astronomer and physicist who established the principle of the pendulum and was first to exploit the telescope.

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Galileo began studying medicine at the University of Pisa but soon turned to his real interests, mathematics, mechanics and astronomy. He became Professor of Mathematics at Pisa at the age of 25 and three years later moved to Padua. In 1610 he transferred to Florence. While still a student he discovered the isochronous property of the pendulum, probably by timing with his pulse the swings of a hanging lamp during a religious ceremony in Pisa Cathedral. He later designed a pendulum-controlled clock, but it was not constructed until after his death, and then not successfully; the first successful pendulum clock was made by the Dutch scientist Christiaan Huygens in 1656. Around 1590 Galileo established the laws of motion of falling bodies, by timing rolling balls down inclined planes and not, as was once widely believed, by dropping different weights from the Leaning Tower of Pisa. These and other observations received definitive treatment in his Discorsi e dimostrazioni matematiche intorno a due nuove scienzi attenenti alla, meccanica (Dialogues Concerning Two New Sciences…) which was completed in 1634 and first printed in 1638. This work also included Galileo's proof that the path of a projectile was a parabola and, most importantly, the development of the concept of inertia.

In astronomy Galileo adopted the Copernican heliocentric theory of the universe while still in his twenties, but he lacked the evidence to promote it publicly. That evidence came with the invention of the telescope by the Dutch brothers Lippershey. Galileo heard of its invention in 1609 and had his own instrument constructed, with a convex object lens and concave eyepiece, a form which came to be known as the Galilean telescope. Galileo was the first to exploit the telescope successfully with a series of striking astronomical discoveries. He was also the first to publish the results of observations with the telescope, in his Sidereus nuncius (Starry Messenger) of 1610. All the discoveries told against the traditional view of the universe inherited from the ancient Greeks, and one in particular, that of the four satellites in orbit around Jupiter, supported the Copernican theory in that it showed that there could be another centre of motion in the universe besides the Earth: if Jupiter, why not the Sun? Galileo now felt confident enough to advocate the theory, but the advance of new ideas was opposed, not for the first or last time, by established opinion, personified in Galileo's time by the ecclesiastical authorities in Rome. Eventually he was forced to renounce the Copernican theory, at least in public, and turn to less contentious subjects such as the "two new sciences" of his last and most important work.

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Bibliography

1610, Sidereus nuncius (Starry Messenger); translation by A.Van Helden, 1989, Sidereus Nuncius, or the Sidereal Messenger; Chicago: University of Chicago Press.

1623, Il Saggiatore (The Assayer).

1632, Dialogo sopre i due massimi sistemi del mondo, tolemaico e copernicano (Dialogue Concerning the Two Chief World Systems, Ptolemaic and Copernican); translation, 1967, Berkeley: University of California Press.

1638, Discorsi e dimostrazioni matematiche intorno a due nuove scienzi attenenti alla

meccanica (Dialogues Concerning Two New Sciences…); translation, 1991, Buffalo, New York: Prometheus Books (reprint).

Further Reading

G.de Santillana, 1955, The Crime of Galileo, Chicago: University of Chicago Press; also 1958, London: Heinemann.

H.Stillman Drake, 1980, Galileo, Oxford: Oxford Paperbacks. M.Sharratt, 1994, Galileo: Decisive Innovator, Oxford: Blackwell.

J.Reston, 1994, Galileo: A Life, New York: HarperCollins; also 1994, London: Cassell.

A.Fantoli, 1994, Galileo: For Copemicanism and for the Church, trans. G.V.Coyne, South Bend, Indiana: University of Notre Dame Press.

LRD