February 15

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Galileo Galilei
1564–1642, Italian Astronomer.


Contributions to Physics

His early studies, at the Univ. of Pisa, were in medicine, but he was soon drawn to mathematics and physics. It is said that at the age of 19, in the cathedral of Pisa, he timed the oscillations of a swinging lamp by means of his pulse beats and found the time for each swing to be the same, no matter what the amplitude of the oscillation, thus discovering the isochronal nature of the pendulum, which he verified by experiment. Galileo soon became known through his invention of a hydrostatic balance and his treatise on the center of gravity of solid bodies. While professor (1589–92) at the Univ. of Pisa, he initiated his experiments concerning the laws of bodies in motion, which brought results so contradictory to the accepted teachings of Aristotle that strong antagonism was aroused. He found that bodies do not fall with velocities proportional to their weights, but he did not arrive at the correct conclusion (that the velocity is proportional to time and independent of both weight and density) until perhaps 20 years later. The famous story in which Galileo is said to have dropped weights from the Leaning Tower of Pisa is apocryphal. The actual experiment was performed by Simon Stevin several years before Galileo's work. However, Galileo did find that the path of a projectile is a parabola, and he is credited with conclusions foreshadowing Newton's laws of motion.

Contributions to Astronomy


Conflict with the Church




See biography by Ludovico Geymonat (tr. 1965); studies by Giorgio de Santillana (1955), Stillman Drake (1970, 1978, and 1980), and W. R. Shea (1973); G. de Santillana, The Crime of Galileo (1955, repr. 1976); Maurice A. Finocchiaro, Galileo and the Art of Reasoning (1980).


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