At the threshold of modern natural science there stands the man who solved the riddle that had puzzled centuries before him, the father of modern astronomy, _Nikolaus Copernicus_. He had studied at the universities of Cracow, Bologna, Ferrara, and Padua, and while he was one of the foremost historians of his time, it was astronomy that had engaged his enthusiastic devotion from his youth. He was a Catholic priest, a Canon of Frauenberg. “If recent representatives of the Roman Church,” so writes the Protestant theologian, _O. Zoeckler_, “praise this Frauenberg Canon as a faithful son of their Church, this fact must be granted by Protestants, despite the frankness with which he opposed the Aristotelian and Ptolemaic theories taught by the scholastics, and despite his friendship with the Protestant _Rheticus_” (Gottes Zeugen im Reiche der Natur, 1906, p. 82). _George Joachim_, a native of Feldkirch, surnamed _Rheticus_, and a Protestant professor at Wittenberg, came to _Copernicus_ at Frauenberg, and was cordially received. His praise for “his teacher” is unreserved. He speaks in the same admiring terms of _Tiedemann Giese_, in those days Bishop of Kulm. For nearly forty years _Copernicus_ sat in the modest observatory which he had erected at Frauenberg, studying and collecting the material for his book. Even after all this time this deliberate scholar, despite the urging of his friends, especially Bishop _Tiedemann Giese_ and Cardinal _Schoenberg_, Archbishop of Capua, hesitated for ten years longer before publishing his discoveries. The work was entitled _De revolutionibus orbium caelestium, libri VI_, and was dedicated to Pope _Paul III._ The author himself could enjoy his achievement but very little. The first copy sent by the printer reached _Copernicus_ on his deathbed, and a few hours later he breathed his last, on May 24, 1543. In the introduction to his work this devout Christian scientist wrote: “Who would not be urged by the intimate intercourse with the work of His hands to the contemplation of the Most High, and to the admiration for the Omnipotent Architect of the universe, in whom is the highest happiness, and in whom is the perfection of all that is good?” Without _Copernicus_ there could have been no _Kepler_, without _Kepler_ no _Newton_. These three men, in the words of a recent astronomer, belong inseparably together, they support and supplement one another. It might be fittingly asked, after which of these three the celestial system should be named; and were it possible to ask these three men for their opinion in this matter, they would probably all give the answer that has been ascribed to one or the other of them: Not my system, but God’s Order. Like _Copernicus_, so _Kepler_ and _Newton_ were profoundly religious men.