Throughout the middle ages the foremost scholars had continued to cherish the astronomical knowledge of the Greeks, which had been conveniently collected and systematized by a celebrated mathematician and scholar living in Egypt in the second century of the Christian era --Ptolemy by name. Among other theories and ideas, Ptolemy taught that the earth is the center of the universe, that revolving about it are the moon, Mercury, Venus, the sun, the other planets, and the fixed stars, and that the entire machine is turned with incredible velocity completely around every twenty-four hours. This so-called Ptolemaic system of astronomy fitted in very nicely with the language of the Bible and with the popular prejudice that the earth remains stationary while the heavenly bodies daily rise and set. It was natural that for many centuries the Christians should accept the views of Ptolemy as almost divinely inspired. [Sidenote: "The Copernican System"] However, a contradictory theory of the solar system was propounded and upheld in the sixteenth century, quite supplanting the Ptolemaic theory in the course of the seventeenth. The new system is called Copernican after its first modern exponent--and its general acceptance went far to annihilate astrology and to place astronomy upon a rational basis. Copernicus [the Latin form of his real name, Koppernigk (1473-1543)] was a native of Poland, who divided his time between official work for the Catholic Church and private researches in astronomy. It was during a ten-year sojourn in Italy (1496-1505), studying canon law and medicine, and familiarizing himself, through humanistic teachers, with ancient Greek astronomers, that Copernicus was led seriously to question the Ptolemaic system and to cast about in search of a truthful substitute. Thenceforth for many years he studied and reflected, but it was not until the year of his death (1543) that his results were published to the world. His book--_On the Revolutions of the Celestial Bodies_, dedicated to Pope Paul III--offered the theory that the earth is not the center of the universe but simply one of a number of planets which revolve about the sun. The earth seemed much less important in the Copernican universe than in the Ptolemaic.