IV GALILEO GALILEI 1564-1642 _Galileo Galilei, born at Pisa, February 15, 1564, was the son of a mathematician who, seeing no future in that profession, had him educated for the practice of medicine. But when Galileo was about eighteen years of age, while observing a large lamp swinging in the Pisa cathedral, he noticed that, regardless of the length of the oscillation, the time did not vary. In spite of his father’s discouragements, therefore, he became absorbed in mathematics and abandoned the study of medicine. Applying himself to the study of motion, he performed his famous experiment of letting bodies of different weights fall from the leaning tower of Pisa, proving that things of unequal weight, if heavier than the resistance of air, fall with the same speed. The doctrine of inertia which he deduced from this and similar experiments decisively answered the opponents of Copernicus; for the principle stated that bodies would continue to move in the same direction forever unless their course was disturbed or opposed by another force, and that the motion of bodies resulted from independent forces operating upon them. His treatise on the center of gravity in solids earned him a lectureship at the University of Pisa._ _Meeting malignant opposition at Pisa, he secured the chair of mathematics at Padua (which he held from 1592 to 1610) and there continued his observations and experiments in physics and chemistry. He succeeded in making a crude thermometer in 1600. In 1609 he learned that Hans Lippershey, an optician of Middleburg, had succeeded in making a telescope. He thereupon made one of his own and improved it until it had a power of magnifying thirty-two times, enabling him to discover the mountainous surface of the moon, the moons of the planet Jupiter, the fact that Venus showed different sides like the moon, and that many small stars made up the Milky Way._ _In 1610 he left Padua for Florence, and by 1613 openly declared his acceptance of Copernican ideas. Immediately he was opposed by theologians, and after being given an opportunity to renounce his adherence to the new system of astronomy, was sentenced in 1616 not to hold, teach, or defend it. In 1623, when his friend Maffeo was made Pope Urban VIII, he wrote his dialogues on the system of the world. He had much difficulty in getting them published and succeeded only when he assured the authorities that they were not heretical. It was quite evident, however, that the dialogues were slightly concealed arguments for the acceptance of the Copernican system and consequently in 1633 he was summoned before the Inquisition and compelled to renounce his heresy. In 1637, a few months after he had discovered the librations of the moon, he lost his sight. He died five years later, January 8, 1642._