CONFLICT BETWEEN NEO-PLATONISM AND CHRISTIANITY.--While the Neo-Platonists were laboring to restore, in modified form, the ancient Greek philosophy and worship, the teachers of Christianity were fast winning the world over to a new faith. The two systems came into deadly antagonism. Christianity triumphed. The gifted and beautiful Hypatia, almost the last representative of the old system of speculation and belief, was torn to pieces in the streets of Alexandria by a mob of fanatic Christian monks (A.D. 415). Finally the Roman emperor Justinian forbade the pagan philosophers to teach their doctrines (A.D. 529). This imperial edict closed forever the Greek schools, in which for more than a thousand years the world had received instruction upon the loftiest themes that can engage the human mind. The Greek philosophers, as living, personal teachers, had finished their work; but their systems of thought will never cease to attract and influence the best minds of the race. SCIENCE AMONG THE GREEKS. The contributions of the Greek observers to the physical sciences have laid us under no small obligation to them. Some of those whom we have classed as philosophers, were careful students of nature, and might be called scientists. The great philosopher Aristotle wrote some valuable works on anatomy and natural history. From his time onward the sciences were pursued with much zeal and success. Especially did the later Greeks do much good and lasting work in the mathematical sciences. MATHEMATICS: EUCLID AND ARCHIMEDES.--Alexandria, in Egypt, became the seat of the most celebrated school of mathematics of antiquity. Here, under Ptolemy Lagus, flourished Euclid, the great geometer, whose work forms the basis of the science of geometry as taught in our schools at the present time. Ptolemy himself was his pupil. The royal student, however, seems to have disliked the severe application required to master the problems of Euclid, and asked his teacher if there was not some easier way. Euclid replied, "There is no royal road to geometry." In the third century B.C., Syracuse, in Sicily, was the home of Archimedes, the greatest mathematician that the Grecian world produced. ASTRONOMY.--Among ancient Greek astronomers, Aristarchus, Hipparchus, and Claudius Ptolemy are distinguished. Aristarchus of Samos, who lived in the third century B.C., held that the earth revolves about the sun as a fixed centre, and rotates on its own axis. He was the Greek Copernicus. But his theory was rejected by his contemporaries and successors. Hipparchus, who flourished about the middle of the second century B.C., was, through his careful observations, the real founder of scientific astronomy. He calculated eclipses, catalogued the stars, and wrote several astronomical works of a really scientific character.