attribute motion to the containing and locating element rather than to the contained and located object, which the earth is. Finally since the planets plainly are at one time nearer and at another time farther from the earth, it would follow, on the theory that the universe revolves, that the movement of the one and same body which is known to take place about a center, that is the center of the earth, must also be directed toward the center from without and from the center outward. The movement about the center must therefore be made more general, and it suffices if that single movement be about its own center. So it appears from all these considerations that the movement of the earth is more probable than its fixity, especially in regard to the daily revolution, which is most peculiar to the earth. FOOTNOTES: [Footnote 4: Selections from the Introduction to _De Orbium Caelestium Revolutionibus_.] III JOHANN KEPLER 1571-1630 _Tycho Brahe (1546-1601), nobleman of Denmark, studied law at the University of Copenhagen and became attracted to astronomical studies by the occurrence of a predicted eclipse. Constructing his own instruments, he made observations of the stars at Augsburg and Wittenberg, and in 1576 established the first observatory at Huen, where he continued his work for twenty years. Banished from Germany, he was invited by Emperor Rudolph to Prague, where he began his compilation of the Rudolphin Tables which listed many of his observations on the locations of the planets. Hearing of Kepler’s interest in astronomy, he secured the young German’s assistance and assigned to him the study of the planet Mars, which study Kepler continued after Tycho Brahe’s death in 1601._ _Johann Kepler, the son of an innkeeper, was born December 27, 1571, in Württemberg and sent to a local school, from which he was removed when he was nine years old because of his father’s impoverishment. After three years of work in the tavern, he was sent to a monastic school and thence to the University of Tübingen. Although he was very frail in physique, he was a good student and attained high scholarly standing. Becoming interested in the Copernican theory, in 1599 he was invited by Tycho Brahe to become his assistant at Prague._