_One of the first and most striking contributions to modern science was the substitution of the Copernican for the Ptolemaic conception of the universe._ _Nicolaus Copernicus was born in the Prussian village of Thorn, located on the Vistula River, February 19, 1473. Although destined for the Church, he became interested in medicine, which he studied at the University of Cracow. Later, he turned to mathematics and continued his studies at the Universities of Vienna, Bologna, Padua, Ferrara, and Rome. Although he settled down as canon at Frauenberg, Poland, and gratuitously practised medicine in conjunction with his ecclesiastical duties, he found considerable time for other intellectual pursuits. Reading widely in the Greek philosophers, he came across a statement that the earth moved in its own orbit. This idea deeply appealed to him. “Occasioned by this,” he wrote, “I also began to think of a motion of the earth, and although the idea seemed absurd, still, as others before me had been permitted to assume certain circles in order to explain the motions of the stars, I believed it would be readily permitted me to try whether on the assumption of some motion of the earth better explanations of the revolutions of the heavenly bodies might not be found. And thus I have, assuming the motions which I in the following work attribute to the earth, after long and careful investigation, finally found that when the motions of the other planets are referred to the circulation of the earth and are computed for the revolution of each star, not only do the phenomena necessarily follow therefrom, but the order and magnitude of the stars and all their orbs and the heaven itself are so connected that in no part can anything be transposed without confusion to the rest and to the whole universe.”_ _In 1530 he issue a “Commentariolus” which outlined his theory, but his prudence prompted him to withhold the publication of his great work, “De Orbium Caelestium Revolutionibus,” until 1543. In May of that year the first printed copy was laid on his death-bed._ THE NEW IDEA OF THE UNIVERSE[4]