Galileo Galilei was born at Pisa on the 18th of February in 1564. His father, Vincenzo Galilei, belonged to a noble family and had gained some distinction as a musician and a mathematician. At an early age, Galileo manifested his ability to learn both mathematical and mechanical types of things, but his parents, wishing to turn him aside from studies which promised no substantial return, steered him toward some sort of medical profession. But this had no effect on Galileo. During his youth he was allowed to follow the path that he wished to.
Although in the popular mind Galileo is remembered chiefly as an astronomer, however, the science of mechanics and dynamics pretty much owe their existence to his findings. Before he was twenty, observation of the oscillations of a swinging lamp in the cathedral of Pisa led him to the discovery of the isochronism of the pendulum, which theory he utilized fifty years later in the construction of an astronomical clock. In 1588, an essay on the center of gravity in solids obtained for him the title of the Archimedes of his time, and secured him a teaching spot in the University of Pisa. During the years immediately following, taking advantage of the celebrated leaning tower, he laid the foundation experimentally of the theory of falling bodies and demonstrated the falsity of the peripatetic maxim, which is that an objects rate of descent is proportional to its weight. When he challenged this it made all of the followers of Aristotle extremely angry, they would not except the fact that their leader could have been wrong. Galileo, in result of this and other troubles, found it prudent to quit Pisa and move to Florence, the original home of his family. In Florence he was nominated by the Venetian Senate in 1592 to the chair of mathematics in the University of Padua, which he occupied for eighteen years, with ever-increasing fame. After that he was appointed philosopher and mathematician to the Grand Duke of Tuscany. During the whole of this period, and to the close of his life, his investigation of Nature, in all her fields, was never stopped. Following up his experiments at Pisa with others upon inclined planes, Galileo established the laws of falling bodies as they are still formulated. He likewise demonstrated the laws of projectiles, and largely anticipated the laws of motion as finally established by Newton. In statics, he gave the first direct and satisfactory demonstration of the laws of equilibrium and the principle of virtual velocities. In hydrostatics, he set forth the true principle of flotation. He invented a thermometer, though a defective one, but he did not, as is sometimes claimed for him, invent the microscope.
Though, as has been said, it is by his astronomical discoveries that he is most widely remembered, it is not these that constitute his most substantial title to fame. In this connection, his greatest achievement was undoubtedly his virtual invention of the telescope. Hearing early in 1609 that a Dutch optician, named Lippershey, had produced an instrument by which the apparent size of remote objects was magnified, Galileo at once realized the principle by which such a result could alone be attained, and, after a single night devoted to consideration of the laws of refraction, he succeeded in constructing a telescope which magnified three times, its magnifying power being soon increased to thirty-two. This instrument being provided and turned towards the heavens, the discoveries, which have made Galileo famous, were bound at once to follow, though undoubtedly he was quick to grasp their full significance. The moon was shown not to be, as the old astronomy taught, a smooth and perfect sphere, of different nature to the earth, but to possess hills and valleys and other features resembling those of our own globe. The planet Jupiter was found to have satellites, thus displaying a solar system in miniature, and supporting the doctrine of Copernicus. It had been argued against the said system that, if it were true, the inferior planets, Venus and Mercury, between the earth and the sun, should in the course of their revolution exhibit phases like those of the moon, and, these being invisible to the naked eye, Copernicus had to change the false explanation that these planets were transparent and the sun's rays passed through them. But with his telescope Galileo found that Venus did actually exhibit the desired phases, and the objection was thus turned into an argument for Copernicanism.
Galileo was tried by the Inquisition for his writings discussing the Ptolemaic and Copernican systems. In June 1633, Galileo was condemned to life imprisonment for heresy. His writings about these subjects were banned, and printers were forbidden to publish anything further by him or even to reprint his previous works. Outside Italy, however, his writings were translated into Latin and were read by scholars throughout Europe.
Galileo remained under imprisonment until his death in 1642. However he never was a real prisoner for he never spent any time in a prison cell or being treated like a criminal. Instead he spent his time in fancy apartments. The rest of the time he was allowed to use houses of friends as his places of confinement the, always comfortable and usually luxurious.
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