PLATO was born at Athens in 429 B.C., the year in which Pericles died. His first literary attempts were in poetry; but his attention was soon turned to philosophy by the teaching of Socrates, whose lectures he began to frequent at about the age of twenty. From that time till the death of Socrates he appears to have lived in the closest intimacy with that philosopher. After that event Plato withdrew to Megara, and subsequently undertook some extensive travels, in the course of which he visited Cyrene, Egypt, Sicily, and Magna Graecia. His intercourse with the elder and the younger Dionysius at Syracuse has been already related His absence from Athens lasted about twelve years; on his return, being then upwards of forty, he began to teach in the gymnasium of the Academy. His doctrines were too recondite for the popular ear, and his lectures were not very numerously attended. But he had a narrower circle of devoted admirers and disciples, consisting of about twenty-eight persons, who met in his private house; over the vestibule of which was inscribed--"Let no one enter who is ignorant of geometry." The most distinguished of this little band of auditors were Speusippus, his nephew and successor, and Aristotle. He died in 347, at the age of 81 or 82, and bequeathed his garden to his school. ARISTOTLE was born in 381 B.C., at Stagira, a seaport town of Chalcidice, whence he is frequently called THE STAGIRITE. At the age of 17, Aristotle, who had then lost both father and mother, repaired to Athens. Plato considered him his best scholar, and called him "the intellect of his school." Aristotle spent twenty years at Athens, during the last ten of which he established a school of his own. In 342 he accepted the invitation of Philip of Macedon to undertake the instruction of his son Alexander. In 335, after Alexander had ascended the throne, Aristotle quitted Macedonia, to which he never returned. He again took up his abode at Athens, where the Athenians assigned him the gymnasium called the Lyceum; and from his habit of delivering his lectures whilst walking up and down in the shady walks of this place, his school was called the PERIPATETIC. In the morning he lectured only to a select class of pupils, called ESOTERIC. His afternoon lectures were delivered to a wider circle, and were therefore called EXOTERIC. It was during the thirteen years in which he presided over the Lyceum that he composed the greater part of his works, and prosecuted his researches in natural history, in which he was most liberally assisted by the munificence of Alexander. The latter portion of Aristotle's life was unfortunate. He appears to have lost from some unknown cause the friendship of Alexander; and, after the death of that monarch, the disturbances which ensued in Greece proved unfavourable to his peace and security. Being threatened with a prosecution for impiety, he escaped from Athens and retired to Chalcis; but he was condemned to