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cal theory: he merely sought to make it
                                         more simple by placing the centre of the
                                         earth’s orbit in the centre of the universe.
                                         This was the point to which the motions of
                                         the planets were referred, for the planes of
                                         their orbits were made to pass through it,
                                         and their points of least and greatest veloc-
                                         ities were also determined with reference to
                                         it. By this arrangement the sun was situate
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