To begin with, it must not be forgotten that we owe the new world system, and with it the turning-point in astronomy, first of all to representatives of the Catholic clergy. After the learned Bishop _Nicholas Oresme_ had expressed with fullest certainty the most important point of the Copernican system as early as 1377 (in a manuscript hitherto unknown, discovered a short time ago by _Pierre Duhem_ in the National Library at Paris. Cfr. Liter. Zentralblatt (1909), page 1618), and after the learned Cardinal _Nicholaus von Kues_ (d. 1474) adopted a rotary motion of the earth in his cosmic system, it was _Copernicus_, a canon of the diocese of Ermland, who became the father of the new theory, in his work “De evolutionibus orbium coelestium.” He published it at the urgent request of Cardinal _Nikolaus Schoenberg_. But the most zealous promoter of his work was Bishop _Tiedemann Giese_ of Kulm. Enthusiastic over the novel idea, he incessantly urged his friend to publish his work, took care of its publication, and sent a copy to Pope _Paul III._, who accepted its dedication. Again, it was a prince of the Church, Bishop _Martin Kromer_, who, in 1851, dedicated a tablet in the cathedral at Frauenberg to “The Great Astronomer and Innovator of Astronomical Science.” All these men knew that _Copernicus_ defended his work not as an hypothesis or as fiction, but as true. Before _Copernicus_ issued his great work, _Clement VIII._ showed a lively interest in his system and had it explained to him by the learned _Johann Widmannstadt_ in the Vatican Gardens (_Pastor_, Gesch. der Päpste, IV, 2 (1907) 550).