Galilei, Galileo
             1564-1642, Italian astronomer, mathematician, and physicist was born in Pisa, Italy. He started Pisa
             University as a medical student in 1581, and became
             professor of mathematics at Padua(1592-1610), where he
             improved the refracting telescope (1610), and was the first person to use astronomy. At the age of 19 he found out the principle of isochronism-that each oscillation of a pendulum takes the same time despite the changes in amplitude. 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 the path of a projectile is a parabola, and he is credited with anticipating Isaac
             Newton's laws of motion. Newton's' three laws of motion are : (1) a body at rest tends to remain at rest, or a body in motion tends to remain in motion at a constant speed in a straight line, unless acted on by an outside force; (2)the acceleration a of a mass m by a force F is directlyproportional to the force and inversely proportional to the
             mass, or a (= (F/m; (3) for every action there is an equaland opposite reaction. The third law implies that the total of a system of bodies not acted on by an external force remains constant.
             1609, he constructed the first astronomical telescope, which he used to discover the four largest satellites of Jupiter and the stellar composition of the Milky Way. In deep study of the theory of refraction; and he prepared a tube, at first of lead, in the ends of which he fitted two lenses, both plane on one side, but on the other side one spherically convex and the other concave. He said, he saw
             objects satisfactorily large and near, for they appeared one-third of the distance off and nine times larger than when they are seen by the naked eye alone. He shortly constr
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