IV 



GALILEO GALILEI 



I 564-1 642 



Galileo Galilei, born at Pisa, February 15, 1564, was the son of a 

 matheryiatician who, seeing no future in that profession, had him 

 educated for the practice of medicine. But when Galileo was aboui 

 eighteen years of age, while observing a large lamp swinging in the 

 Pisa cathedral, he noticed that, regardless of the length of the oscilla- 

 tion, 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 per- 

 formed 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 exper- 

 iments decisively answered the opponents of Copernicus; for the prin- 

 ciple 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 op- 

 erating 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 15Q2 to 1610) and there 

 continued his observations and experiments in physics and chemistry. 

 He succeeded in making a crude- thermometer in 1600. In i6op he 

 learned that Hans Lippershey, an optician of Middleburg, had suc- 

 ceeded 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 lupiter, the fact that Venus showed different 



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