Simon Stevin published Wisconstighe Ghedachtenissen (Mathematical Memoirs) in 1605, which dealt with almost every mathematical fields. One of the interesting contents from Mathematical Memoirs is Van den Hemelloop (The Heavenly Motions). The Heavenly Motions was written with a view to educating Maurice of Nassau who was Stevin’s patron, so it provided elementary geometrical explanations of both Ptolemaic and Copernican astronomy. In comparing the two astronomical assertions Stevin regarded Ptolemaic as false theory and Copernican as true theory. And he gave some natural philosophical accounts for his choice though he was not a philosopher but a mathematician. Moreover he interpreted the data which indicated no parallax could be observed from earth into mathematical way as the evidence for almost infinite dimension of the universe. But Stevin accepted physical reality of celestial spheres which surrounded this enormous universe, and the reason for his acceptance was his idea ‘magnetic rest’ which was developed from his reading of Gilbert’s On Magnet.
Stevin’s cosmological or astronomical attitudes showed the real situations for the contemporary understanding of the universe in the middle period of the astronomical revolution. The understanding of universe in 1600 was very complex and unstable for there were both traditional and new cosmological explanations and there also began to appear various new assertions from many related fields. Stevin and his The Heavenly Motions represented this situation directly and showed mathematicians’ efforts to get better understanding of the shape of universe circa 1600.