wrote during this period. One, in Latin contains the theorems to determine the center of gravity of solid bodies, made him known among mathematicians of his time. The other book, called the Little Balance, was written in Italian. In this book he told how he read the story of Archimedes and the studies of bodies immersed in water.
             In the fall of that year Galileo moved to Pisa where he studied while he continued to teach at the university, in this period he resumed his study of motion and wrote a short book in Latin know as De Motu (On Motion). In De Motu , Galileo tried to disprove some of Aristotle's main views about motion. One of his objections was the assertion that motion, in the absence of the direct action of a force, is maintained by the medium in which it takes place. De Motu represents Galileo's first step in his systematic study of motion and is a key point of reference in Galileo's intellectual development. It shows that Galileo had already started the deep process of original thinking and critical revision of Aristotle's principles that lasted throughout his life.
             At about this time Galileo tried to disprove one particular statement of Aristotle's. Aristotle said that when bodies of the same ma
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