Galileo (Galilei), astronomer, mathematician, and physicist was another of those great anti-Aristotelian scientists of the age, such as Johann Kepler (1571-1630) who also published laws of planetary motion. These great men came to their great discoveries because of their scientific view of Nature. They were a new breed of philosophers, natural philosophers, or scientists as we call them today. They did not dwell long on the useless question: Why do things happen? They asked: "How do things happen?
Galileo was an Italian. At the age of 19 he discovered the principle of isochronism that each oscillation of a pendulum takes the same time despite changes in amplitude. Soon thereafter he became known for his ideas on hydrostatic balance; and, further, his treatise on the center of gravity of falling bodies. He found experimentally that bodies do not fall with velocities proportional to their weights, a conclusion received with hostility because it contradicted the accepted teaching of Aristotle. Galileo discovered that the path of a projectile is a parabola, and he is credited with anticipating Isaac Newton's laws of motion. In 1609 Galileo constructed the first astronomical telescope, which he used to discover the four largest satellites of Jupiter and the stellar composition of the Milky Way, and in 1632 he published his Dialogue Concerning the Two Chief World Systems, a work that upheld the Copernican system rather than the Ptolematic system and marked a turning point in scientific and philosophical thought. Brought (1633) before the Inquisition in Rome, he was made to renounce all his beliefs and writings supporting the Copernican theory.
His last book, Dialogues Concerning Two New Sciences (1638), contains most of Galileo's contributions to physics.
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